* finished refactoring of attribute handling code, especially the

  merging of attributes, such that all tests are passed
* tested and finished implementation of group support in slxconfig
* added new class AttributeRoster which keeps track of the known
  attributes (the ones provided by the openslx core and any other
  ones that may have been added by some plugin).
* added new option --list-attributes to slxconfig which shows information
  about all known attributes


git-svn-id: http://svn.openslx.org/svn/openslx/trunk@1444 95ad53e4-c205-0410-b2fa-d234c58c8868

11 files changed, 1091 insertions, 924 deletions

diff --git a/config-db/OpenSLX/AttributeRoster.pm b/config-db/OpenSLX/AttributeRoster.pm
new file mode 100644
index 00000000..46b90f74
--- /dev/null
+++ b/config-db/OpenSLX/AttributeRoster.pm
@@ -0,0 +1,126 @@
+# Copyright (c) 2006, 2007 - OpenSLX GmbH
+#
+# This program is free software distributed under the GPL version 2.
+# See http://openslx.org/COPYING
+#
+# If you have any feedback please consult http://openslx.org/feedback and
+# send your suggestions, praise, or complaints to feedback@openslx.org
+#
+# General information about OpenSLX can be found at http://openslx.org/
+# -----------------------------------------------------------------------------
+# AttributeRoster.pm
+#	- provides information about all available attributes
+# -----------------------------------------------------------------------------
+package OpenSLX::AttributeRoster;
+
+use strict;
+use warnings;
+
+our (@ISA, @EXPORT, $VERSION);
+
+use Exporter;
+$VERSION = 0.2;
+@ISA = qw(Exporter);
+
+@EXPORT = qw(
+	$%AttributeInfo
+);
+
+use OpenSLX::Basics;
+
+################################################################################
+###
+### Load the available AttrInfo-modules and build a hash containing info about
+### all known attributes from the data contained in those modules.
+###
+################################################################################
+
+my %AttributeInfo = ();
+
+my $libPath = "$openslxConfig{'base-path'}/lib";
+foreach my $module (glob("$libPath/OpenSLX/AttrInfo/*.pm")) {
+	next if $module !~ m{/([^/]+)\.pm$};
+	my $class = "OpenSLX::AttrInfo::$1";
+	vlog(2, "loading attr-info from module '$module'");
+	my $instance = instantiateClass($class);
+	my $attrInfo = $instance->AttrInfo();
+	foreach my $attr (keys %$attrInfo) {
+		$AttributeInfo{$attr} = $attrInfo->{$attr};
+	}
+}
+
+=item C<getAttrInfo()>
+
+Returns info about all attributes.
+
+=over
+
+=item Return Value
+
+An hash-ref with info about all known attributes.
+
+=back
+
+=cut
+
+sub getAttrInfo
+{
+	my $class = shift;
+	my $name  = shift;
+
+	if (defined $name) {
+		my $attrInfo = $AttributeInfo{$name};
+		return if !defined $attrInfo;
+		return { $name => $AttributeInfo{$name} };
+	}
+
+	return \%AttributeInfo;
+}
+
+=item C<getSystemAttrs()>
+
+Returns the attribute names that apply to systems.
+
+=over
+
+=item Return Value
+
+An array of attribute names.
+
+=back
+
+=cut
+
+sub getSystemAttrs
+{
+	my $class = shift;
+
+	return 
+		grep { $AttributeInfo{$_}->{"applies_to_systems"} }
+		keys %AttributeInfo
+}
+
+=item C<getClientAttrs()>
+
+Returns the attribute names that apply to clients.
+
+=over
+
+=item Return Value
+
+An array of attribute names.
+
+=back
+
+=cut
+
+sub getClientAttrs
+{
+	my $class = shift;
+
+	return 
+		grep { $AttributeInfo{$_}->{"applies_to_clients"} }
+		keys %AttributeInfo
+}
+
+1;
diff --git a/config-db/OpenSLX/ConfigDB.pm b/config-db/OpenSLX/ConfigDB.pm
index 289f6f7f..8269ec0c 100644
--- a/config-db/OpenSLX/ConfigDB.pm
+++ b/config-db/OpenSLX/ConfigDB.pm
@@ -16,6 +16,8 @@ use warnings;
 our (@ISA, @EXPORT_OK, %EXPORT_TAGS, $VERSION);
 $VERSION = 1;    # API-version
 
+use Storable qw(dclone);
+
 use Exporter;
 @ISA = qw(Exporter);
 
@@ -81,7 +83,7 @@ to filtering (with boolean operators and hierarchical expressions)].
 =cut
 
 my @supportExports = qw(
-  isAttribute mergeAttributes pushAttributes
+  mergeAttributes pushAttributes
   externalIDForSystem externalIDForClient externalConfigNameForClient
   externalAttrName generatePlaceholderFor
 );
@@ -112,6 +114,7 @@ sub new
 	my $class = shift;
 
 	my $self = {
+		'db-schema' => OpenSLX::DBSchema->new,
 	};
 
 	return bless $self, $class;
@@ -182,7 +185,7 @@ sub connect		## no critic (ProhibitBuiltinHomonyms)
 	$self->{'db-type'} = $dbType;
 	$self->{'meta-db'} = $metaDB;
 
-	$self->_checkAndUpgradeDBSchemaIfNecessary($metaDB);
+	$self->{'db-schema'}->checkAndUpgradeDBSchemaIfNecessary($metaDB);
 
 	return 1;
 }
@@ -281,55 +284,7 @@ sub getColumnsOfTable
 	my $self      = shift;
 	my $tableName = shift;
 
-	return	
-		map { (/^(\w+)\W/) ? $1 : $_; } 
-		@{$DbSchema->{tables}->{$tableName}->{cols}};
-}
-
-=item C<getKnownSystemAttrs()>
-
-Returns the attribute names that apply to systems.
-
-=over
-
-=item Return Value
-
-An array of attribute names.
-
-=back
-
-=cut
-
-sub getKnownSystemAttrs
-{
-	my $self = shift;
-
-	return 
-		grep { $AttributeInfo{$_}->{"applies_to_systems"} }
-		keys %AttributeInfo
-}
-
-=item C<getKnownClientAttrs()>
-
-Returns the attribute names that apply to clients.
-
-=over
-
-=item Return Value
-
-An array of attribute names.
-
-=back
-
-=cut
-
-sub getKnownClientAttrs
-{
-	my $self = shift;
-
-	return 
-		grep { $AttributeInfo{$_}->{"applies_to_clients"} }
-		keys %AttributeInfo
+	return $self->{'db-schema'}->getColumnsOfTable($tableName);
 }
 
 =item C<fetchVendorOSByFilter([%$filter], [$resultCols])>
@@ -1243,10 +1198,12 @@ The IDs of the new system(s), C<undef> if the creation failed.
 
 sub addSystem
 {
-	my $self    = shift;
-	my $valRows = _aref(shift);
+	my $self      = shift;
+	my $inValRows = _aref(shift);
 
-	_checkCols($valRows, 'system', qw(name export_id));
+	_checkCols($inValRows, 'system', qw(name export_id));
+
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
 
 	foreach my $valRow (@$valRows) {
 		if (!$valRow->{kernel}) {
@@ -1264,7 +1221,7 @@ sub addSystem
 		}
 	}
 
-	return $self->{'meta-db'}->addSystem($valRows);
+	return $self->{'meta-db'}->addSystem($valRows, $attrValRows);
 }
 
 =item C<removeSystem(@$systemIDs)>
@@ -1324,48 +1281,50 @@ sub changeSystem
 {
 	my $self      = shift;
 	my $systemIDs = _aref(shift);
-	my $valRows   = _aref(shift);
+	my $inValRows = _aref(shift);
 
-	return $self->{'meta-db'}->changeSystem($systemIDs, $valRows);
-}
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
 
-=item C<setSystemAttr($systemID, $attrName, $attrValue)>
-
-Sets a value for an attribute of the given system. If the system already
-has a value for this attribute, it will be overwritten.
-
-=over
-
-=item Param C<systemID>
-
-The ID of the system whose attribute shall be changed.
-
-=item Param C<attrName>
-
-The name of the attribute to change.
-
-=item Param C<attrValue>
-
-The new value for the attribute.
-
-=item Return Value
-
-C<1> if the attribute could be set, C<undef> if not.
-
-=back
-
-=cut
-
-sub setSystemAttr
-{
-	my $self      = shift;
-	my $systemID  = shift;
-	my $attrName  = shift;
-	my $attrValue = shift;
-
-	return $self->{'meta-db'}->setSystemAttr($systemID, $attrName, $attrValue);
+	return $self->{'meta-db'}->changeSystem($systemIDs, $valRows, $attrValRows);
 }
 
+#=item C<setSystemAttr($systemID, $attrName, $attrValue)>
+#
+#Sets a value for an attribute of the given system. If the system already
+#has a value for this attribute, it will be overwritten.
+#
+#=over
+#
+#=item Param C<systemID>
+#
+#The ID of the system whose attribute shall be changed.
+#
+#=item Param C<attrName>
+#
+#The name of the attribute to change.
+#
+#=item Param C<attrValue>
+#
+#The new value for the attribute.
+#
+#=item Return Value
+#
+#C<1> if the attribute could be set, C<undef> if not.
+#
+#=back
+#
+#=cut
+#
+#sub setSystemAttr
+#{
+#	my $self      = shift;
+#	my $systemID  = shift;
+#	my $attrName  = shift;
+#	my $attrValue = shift;
+#
+#	return $self->{'meta-db'}->setSystemAttr($systemID, $attrName, $attrValue);
+#}
+
 =item C<setClientIDsOfSystem($systemID, @$clientIDs)>
 
 Specifies all clients that should offer the given system for booting.
@@ -1608,10 +1567,12 @@ The IDs of the new client(s), C<undef> if the creation failed.
 
 sub addClient
 {
-	my $self    = shift;
-	my $valRows = _aref(shift);
+	my $self      = shift;
+	my $inValRows = _aref(shift);
+
+	_checkCols($inValRows, 'client', qw(name mac));
 
-	_checkCols($valRows, 'client', qw(name mac));
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
 
 	foreach my $valRow (@$valRows) {
 		if (!$valRow->{boot_type}) {
@@ -1619,7 +1580,7 @@ sub addClient
 		}
 	}
 
-	return $self->{'meta-db'}->addClient($valRows);
+	return $self->{'meta-db'}->addClient($valRows, $attrValRows);
 }
 
 =item C<removeClient(@$clientIDs)>
@@ -1679,48 +1640,50 @@ sub changeClient
 {
 	my $self      = shift;
 	my $clientIDs = _aref(shift);
-	my $valRows   = _aref(shift);
-
-	return $self->{'meta-db'}->changeClient($clientIDs, $valRows);
-}
-
-=item C<setClientAttr($clientID, $attrName, $attrValue)>
-
-Sets a value for an attribute of the given client. If the client already
-has a value for this attribute, it will be overwritten.
-
-=over
-
-=item Param C<clientID>
-
-The ID of the client whose attribute shall be changed.
-
-=item Param C<attrName>
-
-The name of the attribute to change.
-
-=item Param C<attrValue>
-
-The new value for the attribute.
-
-=item Return Value
-
-C<1> if the attribute could be set, C<undef> if not.
-
-=back
-
-=cut
+	my $inValRows = _aref(shift);
 
-sub setClientAttr
-{
-	my $self      = shift;
-	my $clientID  = shift;
-	my $attrName  = shift;
-	my $attrValue = shift;
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
 
-	return $self->{'meta-db'}->setClientAttr($clientID, $attrName, $attrValue);
+	return $self->{'meta-db'}->changeClient($clientIDs, $valRows, $attrValRows);
 }
 
+#=item C<setClientAttr($clientID, $attrName, $attrValue)>
+#
+#Sets a value for an attribute of the given client. If the client already
+#has a value for this attribute, it will be overwritten.
+#
+#=over
+#
+#=item Param C<clientID>
+#
+#The ID of the client whose attribute shall be changed.
+#
+#=item Param C<attrName>
+#
+#The name of the attribute to change.
+#
+#=item Param C<attrValue>
+#
+#The new value for the attribute.
+#
+#=item Return Value
+#
+#C<1> if the attribute could be set, C<undef> if not.
+#
+#=back
+#
+#=cut
+#
+#sub setClientAttr
+#{
+#	my $self      = shift;
+#	my $clientID  = shift;
+#	my $attrName  = shift;
+#	my $attrValue = shift;
+#
+#	return $self->{'meta-db'}->setClientAttr($clientID, $attrName, $attrValue);
+#}
+
 =item C<setSystemIDsOfClient($clientID, @$systemIDs)>
 
 Specifies all systems that should be offered for booting by the given client.
@@ -1957,17 +1920,19 @@ The IDs of the new group(s), C<undef> if the creation failed.
 
 sub addGroup
 {
-	my $self    = shift;
-	my $valRows = _aref(shift);
+	my $self      = shift;
+	my $inValRows = _aref(shift);
+
+	_checkCols($inValRows, 'group', qw(name));
 
-	_checkCols($valRows, 'group', qw(name));
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
 
 	foreach my $valRow (@$valRows) {
 		if (!defined $valRow->{priority}) {
 			$valRow->{priority} = '50';
 		}
 	}
-	return $self->{'meta-db'}->addGroup($valRows);
+	return $self->{'meta-db'}->addGroup($valRows, $attrValRows);
 }
 
 =item C<removeGroup(@$groupIDs)>
@@ -2001,42 +1966,42 @@ sub removeGroup
 	return $self->{'meta-db'}->removeGroup($groupIDs);
 }
 
-=item C<setGroupAttr($groupID, $attrName, $attrValue)>
-
-Sets a value for an attribute of the given group. If the group already
-has a value for this attribute, it will be overwritten.
-
-=over
-
-=item Param C<groupID>
-
-The ID of the group whose attribute shall be changed.
-
-=item Param C<attrName>
-
-The name of the attribute to change.
-
-=item Param C<attrValue>
-
-The new value for the attribute.
-
-=item Return Value
-
-C<1> if the attribute could be set, C<undef> if not.
-
-=back
-
-=cut
-
-sub setGroupAttr
-{
-	my $self      = shift;
-	my $groupID  = shift;
-	my $attrName  = shift;
-	my $attrValue = shift;
-
-	return $self->{'meta-db'}->setGroupAttr($groupID, $attrName, $attrValue);
-}
+#=item C<setGroupAttr($groupID, $attrName, $attrValue)>
+#
+#Sets a value for an attribute of the given group. If the group already
+#has a value for this attribute, it will be overwritten.
+#
+#=over
+#
+#=item Param C<groupID>
+#
+#The ID of the group whose attribute shall be changed.
+#
+#=item Param C<attrName>
+#
+#The name of the attribute to change.
+#
+#=item Param C<attrValue>
+#
+#The new value for the attribute.
+#
+#=item Return Value
+#
+#C<1> if the attribute could be set, C<undef> if not.
+#
+#=back
+#
+#=cut
+#
+#sub setGroupAttr
+#{
+#	my $self      = shift;
+#	my $groupID  = shift;
+#	my $attrName  = shift;
+#	my $attrValue = shift;
+#
+#	return $self->{'meta-db'}->setGroupAttr($groupID, $attrName, $attrValue);
+#}
 
 =item C<changeGroup(@$groupIDs, @$valRows)>
 
@@ -2062,11 +2027,13 @@ C<1> if the group(s) could be changed, C<undef> if not.
 
 sub changeGroup
 {
-	my $self     = shift;
-	my $groupIDs = _aref(shift);
-	my $valRows  = _aref(shift);
+	my $self      = shift;
+	my $groupIDs  = _aref(shift);
+	my $inValRows = _aref(shift);
 
-	return $self->{'meta-db'}->changeGroup($groupIDs, $valRows);
+	my ($valRows, $attrValRows) = _cloneAndUnhingeAttrs($inValRows);
+
+	return $self->{'meta-db'}->changeGroup($groupIDs, $valRows, $attrValRows);
 }
 
 =item C<setClientIDsOfGroup($groupID, @$clientIDs)>
@@ -2525,7 +2492,7 @@ sub aggregatedSystemFileInfoFor
 	my $self   = shift;
 	my $system = shift;
 
-	my $info = {%$system};
+	my $info = dclone($system);
 
 	my $export = $self->fetchExportByID($system->{export_id});
 	if (!defined $export) {
@@ -2586,32 +2553,6 @@ sub aggregatedSystemFileInfoFor
 
 =over
 
-=item C<isAttribute($key)>
-
-Returns whether or not the given key is an exportable attribute.
-
-=over
-
-=item Param C<system>
-
-The key to check.
-
-=item Return Value
-
-1 if the given key is indeed an attribute (currently, this means that
-it starts with 'attr_'), 0 if not.
-
-=back
-
-=cut
-
-sub isAttribute
-{
-	my $key = shift;
-
-	return $key =~ m[^attr_];
-}
-
 =item C<mergeAttributes($target, $source)>
 
 Copies all attributes from source that are unset in target over (source extends target).
@@ -2648,7 +2589,7 @@ sub mergeAttributes
 		my $sourceVal = $sourceAttrs->{$key};
 		my $targetVal = $targetAttrs->{$key};
 		if (defined $sourceVal && !defined $targetVal) {
-			vlog(0, _tr("merging %s (val=%s)", $key, $sourceVal));
+			vlog(3, _tr("merging %s (val=%s)", $key, $sourceVal));
 			$targetAttrs->{$key} = $sourceVal;
 		}
 	}
@@ -2851,51 +2792,6 @@ sub generatePlaceholderFor
 ################################################################################
 ### private stuff
 ################################################################################
-sub _checkAndUpgradeDBSchemaIfNecessary
-{
-	my $self   = shift;
-	my $metaDB = shift;
-
-	vlog(2, "trying to determine schema version...");
-	my $currVersion = $metaDB->schemaFetchDBVersion();
-	if (!defined $currVersion) {
-		# that's bad, someone has messed with our DB: there is a
-		# database, but the 'meta'-table is empty. 
-		# There might still be data in the other tables, but we have no way to 
-		# find out which schema version they're in. So it's safer to give up.
-		croak _tr('Could not determine schema version of database');
-	}
-
-	if ($currVersion == 0) {
-		vlog(1, _tr('Creating DB (schema version: %s)', $DbSchema->{version}));
-		foreach my $tableName (keys %{$DbSchema->{tables}}) {
-			# create table (optionally inserting default values, too)
-			$metaDB->schemaAddTable(
-				$tableName,
-				$DbSchema->{tables}->{$tableName}->{cols},
-				$DbSchema->{tables}->{$tableName}->{vals}
-			);
-		}
-		$metaDB->schemaSetDBVersion($DbSchema->{version});
-		vlog(1, _tr('DB has been created successfully'));
-	} elsif ($currVersion < $DbSchema->{version}) {
-		vlog(
-			1,
-			_tr(
-				'Our schema-version is %s, DB is %s, upgrading DB...',
-				$DbSchema->{version}, $currVersion
-			)
-		);
-		$metaDB->schemaUpgradeDBFrom($currVersion);
-		$metaDB->schemaSetDBVersion($DbSchema->{version});
-		vlog(1, _tr('upgrade done'));
-	} else {
-		vlog(1, _tr('DB matches current schema version (%s)', $currVersion));
-	}
-
-	return 1;
-}
-
 sub _aref
 {    # transparently converts the given reference to an array-ref
 	my $ref = shift;
@@ -2927,4 +2823,20 @@ sub _checkCols
 	return 1;
 }
 
+sub _cloneAndUnhingeAttrs
+{
+	my $inValRows = shift;
+
+	# clone data and unhinge attrs
+	my (@valRows, @attrValRows);
+	foreach my $inValRow (@$inValRows) {
+		push @attrValRows, $inValRow->{attrs};
+		my $valRow = dclone($inValRow);
+		delete $valRow->{attrs};
+		push @valRows, $valRow;
+	}
+
+	return (\@valRows, \@attrValRows);
+}
+
 1;
diff --git a/config-db/OpenSLX/Export/DHCP/ISC.pm b/config-db/OpenSLX/ConfigExport/DHCP/ISC.pm
index 2e7aa01b..e3dd0738 100644
--- a/config-db/OpenSLX/Export/DHCP/ISC.pm
+++ b/config-db/OpenSLX/ConfigExport/DHCP/ISC.pm
@@ -11,7 +11,7 @@
 # ISC.pm
 #	- provides ISC-specific implementation of DHCP export.
 # -----------------------------------------------------------------------------
-package OpenSLX::Export::DHCP::ISC;
+package OpenSLX::ConfigExport::DHCP::ISC;
 
 use strict;
 use warnings;
diff --git a/config-db/OpenSLX/DBSchema.pm b/config-db/OpenSLX/DBSchema.pm
index 801f50a9..cd92c07e 100644
--- a/config-db/OpenSLX/DBSchema.pm
+++ b/config-db/OpenSLX/DBSchema.pm
@@ -16,25 +16,8 @@ package OpenSLX::DBSchema;
 use strict;
 use warnings;
 
-our (@ISA, @EXPORT, $VERSION);
-
-use Exporter;
-$VERSION = 0.2;
-@ISA = qw(Exporter);
-
-@EXPORT = qw(
-	$DbSchema %DbSchemaHistory %AttributeInfo
-);
-
-our ($DbSchema, %DbSchemaHistory, %AttributeInfo);
-
-
 use OpenSLX::Basics;
 
-use POSIX qw(locale_h);
-my $lang = setlocale(LC_MESSAGES);
-my $country = $lang =~ m[^\w\w_(\w\w)] ? lc($1) : 'us';
-
 ################################################################################
 ### DB-schema definition
 ### 	This hash-ref describes the current OpenSLX configuration database 
@@ -51,7 +34,13 @@ my $country = $lang =~ m[^\w\w_(\w\w)] ? lc($1) : 'us';
 ### 		fk		=> foreign key (integer)
 ################################################################################
 
-$DbSchema = {
+use POSIX qw(locale_h);
+my $lang = setlocale(LC_MESSAGES);
+my $country = $lang =~ m[^\w\w_(\w\w)] ? lc($1) : 'us';
+
+my $VERSION = 0.2;
+
+my $DbSchema = {
 	'version' => $VERSION,
 	'tables' => {
 		'client' => {
@@ -170,7 +159,7 @@ $DbSchema = {
 			],
 			'vals' => [
 				{
-					'schema_version' => $DbSchema->{'version'},
+					'schema_version' => $VERSION,
 				},
 			],
 		},
@@ -213,16 +202,6 @@ $DbSchema = {
 				# attributes of default system
 				{
 					'system_id' => 0,
-					'name' => 'automnt_dir',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'automnt_src',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
 					'name' => 'country',
 					'value' => "$country",
 				},
@@ -233,21 +212,6 @@ $DbSchema = {
 				},
 				{
 					'system_id' => 0,
-					'name' => 'hw_graphic',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'hw_monitor',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'hw_mouse',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
 					'name' => 'late_dm',
 					'value' => 'no',
 				},
@@ -258,52 +222,12 @@ $DbSchema = {
 				},
 				{
 					'system_id' => 0,
-					'name' => 'nis_domain',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'nis_servers',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'ramfs_fsmods',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'ramfs_miscmods',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
 					'name' => 'ramfs_nicmods',
 					'value' 
 						=> 'forcedeth e1000 e100 tg3 via-rhine r8169 pcnet32',
 				},
 				{
 					'system_id' => 0,
-					'name' => 'ramfs_screen',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'sane_scanner',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'scratch',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
-					'name' => 'slxgrp',
-					'value' => '',
-				},
-				{
-					'system_id' => 0,
 					'name' => 'start_alsasound',
 					'value' => 'yes',
 				},
@@ -409,23 +333,301 @@ $DbSchema = {
 
 ################################################################################
 ###
-### Load the available AttrInfo-modules and build a hash containing info about
-### all known attributes from the data contained in those modules.
+### standard methods
+###
+################################################################################
+sub new
+{
+	my $class = shift;
+
+	my $self = {
+	};
+
+	return bless $self, $class;
+}
+
+sub checkAndUpgradeDBSchemaIfNecessary
+{
+	my $self   = shift;
+	my $metaDB = shift;
+
+	vlog(2, "trying to determine schema version...");
+	my $currVersion = $metaDB->schemaFetchDBVersion();
+	if (!defined $currVersion) {
+		# that's bad, someone has messed with our DB: there is a
+		# database, but the 'meta'-table is empty. 
+		# There might still be data in the other tables, but we have no way to 
+		# find out which schema version they're in. So it's safer to give up.
+		croak _tr('Could not determine schema version of database');
+	}
+
+	if ($currVersion == 0) {
+		vlog(1, _tr('Creating DB (schema version: %s)', $DbSchema->{version}));
+		foreach my $tableName (keys %{$DbSchema->{tables}}) {
+			# create table (optionally inserting default values, too)
+			$metaDB->schemaAddTable(
+				$tableName,
+				$DbSchema->{tables}->{$tableName}->{cols},
+				$DbSchema->{tables}->{$tableName}->{vals}
+			);
+		}
+		$metaDB->schemaSetDBVersion($DbSchema->{version});
+		vlog(1, _tr('DB has been created successfully'));
+	} elsif ($currVersion < $DbSchema->{version}) {
+		vlog(
+			1,
+			_tr(
+				'Our schema-version is %s, DB is %s, upgrading DB...',
+				$DbSchema->{version}, $currVersion
+			)
+		);
+		$self->_schemaUpgradeDBFrom($metaDB, $currVersion);
+		$metaDB->schemaSetDBVersion($DbSchema->{version});
+		vlog(1, _tr('upgrade done'));
+	} else {
+		vlog(1, _tr('DB matches current schema version (%s)', $currVersion));
+	}
+
+	return 1;
+}
+
+sub getColumnsOfTable
+{
+	my $self      = shift;
+	my $tableName = shift;
+
+	return	
+		map { (/^(\w+)\W/) ? $1 : $_; } 
+		@{$DbSchema->{tables}->{$tableName}->{cols}};
+}
+
+################################################################################
+###
+### methods for upgrading the DB schema
 ###
 ################################################################################
+sub _schemaUpgradeDBFrom
+{
+	my $self        = shift;
+	my $metaDB      = shift;
+	my $currVersion = shift;
 
-%AttributeInfo = ();
+	$self->_upgradeDBTo0_2($metaDB) if $currVersion < 0.2;
+
+	return 1;
+}
 
-my $libPath = "$openslxConfig{'base-path'}/lib";
-foreach my $module (glob("$libPath/OpenSLX/AttrInfo/*.pm")) {
-	next if $module !~ m{/([^/]+)\.pm$};
-	my $class = "OpenSLX::AttrInfo::$1";
-	vlog(2, "loading attr-info from module '$module'");
-	my $instance = instantiateClass($class);
-	my $attrInfo = $instance->AttrInfo();
-	foreach my $attr (keys %$attrInfo) {
-		$AttributeInfo{$attr} = $attrInfo->{$attr};
+sub _upgradeDBTo0_2
+{
+	my $self   = shift;
+	my $metaDB = shift;
+
+	# move attributes into separate tables ...
+	#
+	# ... system attributes ...
+	$metaDB->schemaAddTable(
+		'system_attr', 
+		[
+			'id:pk',
+			'system_id:fk',
+			'name:s.128',
+			'value:s.255',
+		]
+	);
+	foreach my $system ($metaDB->fetchSystemByFilter()) {
+		my %attrs;
+		foreach my $key (keys %$system) {
+			next if substr($key, 0, 5) ne 'attr_';
+			my $attrValue = $system->{$key} || '';
+			next if $system->{id} > 0 && !length($attrValue);
+			my $newAttrName = substr($key, 5);
+			$attrs{$newAttrName} = $attrValue;
+		}
+		$metaDB->setSystemAttrs($system->{id}, \%attrs);
+	}
+	$metaDB->schemaDropColumns(
+		'system',
+		[
+			'attr_automnt_dir',
+			'attr_automnt_src',
+			'attr_country',
+			'attr_dm_allow_shutdown',
+			'attr_hw_graphic',
+			'attr_hw_monitor',
+			'attr_hw_mouse',
+			'attr_late_dm',
+			'attr_netbios_workgroup',
+			'attr_nis_domain',
+			'attr_nis_servers',
+			'attr_ramfs_fsmods',
+			'attr_ramfs_miscmods',
+			'attr_ramfs_nicmods',
+			'attr_ramfs_screen',
+			'attr_sane_scanner',
+			'attr_scratch',
+			'attr_slxgrp',
+			'attr_start_alsasound',
+			'attr_start_atd',
+			'attr_start_cron',
+			'attr_start_dreshal',
+			'attr_start_ntp',
+			'attr_start_nfsv4',
+			'attr_start_printer',
+			'attr_start_samba',
+			'attr_start_snmp',
+			'attr_start_sshd',
+			'attr_start_syslog',
+			'attr_start_x',
+			'attr_start_xdmcp',
+			'attr_tex_enable',
+			'attr_timezone',
+			'attr_tvout',
+			'attr_vmware',
+		],
+		[
+			'id:pk',
+			'export_id:fk',
+			'name:s.64',
+			'label:s.64',
+			'kernel:s.128',
+			'kernel_params:s.512',
+			'hidden:b',
+			'comment:s.1024',
+		]
+	);
+	#
+	# ... client attributes ...
+	$metaDB->schemaAddTable(
+		'client_attr',
+		[
+			'id:pk',
+			'client_id:fk',
+			'name:s.128',
+			'value:s.255',
+		]
+	);
+	foreach my $client ($metaDB->fetchClientByFilter()) {
+		my %attrs;
+		foreach my $key (keys %$client) {
+			next if substr($key, 0, 5) ne 'attr_';
+			my $attrValue = $client->{$key} || '';
+			next if !length($attrValue);
+			my $newAttrName = substr($key, 5);
+			$attrs{$newAttrName} = $attrValue;
+		}
+		$metaDB->setClientAttrs($client->{id}, \%attrs);
 	}
+	$metaDB->schemaDropColumns(
+		'client',
+		[
+			'attr_automnt_dir',
+			'attr_automnt_src',
+			'attr_country',
+			'attr_dm_allow_shutdown',
+			'attr_hw_graphic',
+			'attr_hw_monitor',
+			'attr_hw_mouse',
+			'attr_late_dm',
+			'attr_netbios_workgroup',
+			'attr_nis_domain',
+			'attr_nis_servers',
+			'attr_sane_scanner',
+			'attr_scratch',
+			'attr_slxgrp',
+			'attr_start_alsasound',
+			'attr_start_atd',
+			'attr_start_cron',
+			'attr_start_dreshal',
+			'attr_start_ntp',
+			'attr_start_nfsv4',
+			'attr_start_printer',
+			'attr_start_samba',
+			'attr_start_snmp',
+			'attr_start_sshd',
+			'attr_start_syslog',
+			'attr_start_x',
+			'attr_start_xdmcp',
+			'attr_tex_enable',
+			'attr_timezone',
+			'attr_tvout',
+			'attr_vmware',
+		],
+		[
+			'id:pk',
+			'name:s.128',
+			'mac:s.20',
+			'boot_type:s.20',
+			'unbootable:b',
+			'kernel_params:s.128',
+			'comment:s.1024',
+		]
+	);
+	#
+	# ... group attributes ...
+	$metaDB->schemaAddTable(
+		'group_attr',
+		[
+			'id:pk',
+			'group_id:fk',
+			'name:s.128',
+			'value:s.255',
+		]
+	);
+	foreach my $group ($metaDB->fetchGroupByFilter()) {
+		my %attrs;
+		foreach my $key (keys %$group) {
+			next if substr($key, 0, 5) ne 'attr_';
+			my $attrValue = $group->{$key} || '';
+			next if !length($attrValue);
+			my $newAttrName = substr($key, 5);
+			$attrs{$newAttrName} = $attrValue;
+		}
+		$metaDB->setGroupAttrs($group->{id}, \%attrs);
+	}
+	$metaDB->schemaDropColumns(
+		'groups',
+		[
+			'attr_automnt_dir',
+			'attr_automnt_src',
+			'attr_country',
+			'attr_dm_allow_shutdown',
+			'attr_hw_graphic',
+			'attr_hw_monitor',
+			'attr_hw_mouse',
+			'attr_late_dm',
+			'attr_netbios_workgroup',
+			'attr_nis_domain',
+			'attr_nis_servers',
+			'attr_sane_scanner',
+			'attr_scratch',
+			'attr_slxgrp',
+			'attr_start_alsasound',
+			'attr_start_atd',
+			'attr_start_cron',
+			'attr_start_dreshal',
+			'attr_start_ntp',
+			'attr_start_nfsv4',
+			'attr_start_printer',
+			'attr_start_samba',
+			'attr_start_snmp',
+			'attr_start_sshd',
+			'attr_start_syslog',
+			'attr_start_x',
+			'attr_start_xdmcp',
+			'attr_tex_enable',
+			'attr_timezone',
+			'attr_tvout',
+			'attr_vmware',
+		],
+		[
+			'id:pk',
+			'name:s.128',
+			'priority:i',
+			'comment:s.1024',
+		]
+	);
+
+	return 1;
 }
 
 1;
diff --git a/config-db/OpenSLX/MetaDB/DBI.pm b/config-db/OpenSLX/MetaDB/DBI.pm
index 98754777..a6d2eef0 100644
--- a/config-db/OpenSLX/MetaDB/DBI.pm
+++ b/config-db/OpenSLX/MetaDB/DBI.pm
@@ -713,24 +713,16 @@ sub changeGlobalInfo
 
 sub addSystem
 {
-	my $self    = shift;
-	my $valRows = shift;
-
-	# separate the attribute hashes ...
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	my $self        = shift;
+	my $valRows     = shift;
+	my $attrValRows = shift;
 
 	# ... store the systems to get the IDs ...
 	my @systemIDs = $self->_doInsert('system', $valRows);
 
 	# ... finally store the individual attribute sets
 	foreach my $id (@systemIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setSystemAttrs($id, $attrs);
 	}
@@ -751,17 +743,11 @@ sub changeSystem
 	my $self      = shift;
 	my $systemIDs = shift;
 	my $valRows   = shift;
+	my $attrValRows = shift;
 
-	# separate the attribute hashes and store them individually
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	# store the attribute hashes individually
 	foreach my $id (@$systemIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setSystemAttrs($id, $attrs);
 	}
@@ -776,20 +762,21 @@ sub setSystemAttrs
 	my $systemID = shift;
 	my $attrs    = shift;
 
-	# we take the simple path and remove all attributes ...
+	# for now we take the simple path and remove all attributes ...
 	return if !$self->_doDelete('system_attr', [ $systemID ], 'system_id');
 
 	# ... and (re-)insert the given ones
-	foreach my $key (keys %$attrs) {
-		return if !$self->_doInsert(
-			'system_attr', [ {
-				system_id => $systemID,
-				name      => $key,
-				value     => $attrs->{$key},
-			} ]
-		);
-	}
-	return 1;
+	my @attrData 
+		=	map {
+				{
+					system_id => $systemID,
+					name      => $_,
+					value     => $attrs->{$_},
+				}			
+			}
+			grep { defined $attrs->{$_} }
+			keys %$attrs;
+	return $self->_doInsert('system_attr', [ @attrData ]);
 }
 
 sub setClientIDsOfSystem
@@ -822,22 +809,14 @@ sub addClient
 {
 	my $self    = shift;
 	my $valRows = shift;
-
-	# separate the attribute hashes ...
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	my $attrValRows = shift;
 
 	# ... store the clients to get the IDs ...
 	my @clientIDs = $self->_doInsert('client', $valRows);
 
 	# ... finally store the individual attribute sets
 	foreach my $id (@clientIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setClientAttrs($id, $attrs);
 	}
@@ -855,20 +834,14 @@ sub removeClient
 
 sub changeClient
 {
-	my $self      = shift;
-	my $clientIDs = shift;
-	my $valRows   = shift;
+	my $self        = shift;
+	my $clientIDs   = shift;
+	my $valRows     = shift;
+	my $attrValRows = shift;
 
-	# separate the attribute hashes and store them individually
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	# store the attribute hashes individually
 	foreach my $id (@$clientIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setClientAttrs($id, $attrs);
 	}
@@ -883,19 +856,21 @@ sub setClientAttrs
 	my $clientID = shift;
 	my $attrs    = shift;
 
-	# we take the simple path and remove all attributes ...
+	# for now we take the simple path and remove all attributes ...
 	return if !$self->_doDelete('client_attr', [ $clientID ], 'client_id');
 
 	# ... and (re-)insert the given ones
-	foreach my $key (keys %$attrs) {
-		return if !$self->_doInsert(
-			'client_attr', [ {
-				client_id => $clientID,
-				name      => $key,
-				value     => $attrs->{$key},
-			} ]
-		);
-	}
+	my @attrData 
+		=	map {
+				{
+					client_id => $clientID,
+					name      => $_,
+					value     => $attrs->{$_},
+				}			
+			}
+			grep { defined $attrs->{$_} }
+			keys %$attrs;
+	return $self->_doInsert('client_attr', [ @attrData ]);
 	return 1;
 }
 
@@ -927,24 +902,16 @@ sub setGroupIDsOfClient
 
 sub addGroup
 {
-	my $self    = shift;
-	my $valRows = shift;
-
-	# separate the attribute hashes ...
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	my $self        = shift;
+	my $valRows     = shift;
+	my $attrValRows = shift;
 
 	# ... store the groups to get the IDs ...
 	my @groupIDs = $self->_doInsert('groups', $valRows);
 
 	# ... finally store the individual attribute sets
 	foreach my $id (@groupIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setGroupAttrs($id, $attrs);
 	}
@@ -962,20 +929,14 @@ sub removeGroup
 
 sub changeGroup
 {
-	my $self     = shift;
-	my $groupIDs = shift;
-	my $valRows  = shift;
+	my $self        = shift;
+	my $groupIDs    = shift;
+	my $valRows     = shift;
+	my $attrValRows = shift;
 
-	# separate the attribute hashes and store them individually
-	my @attrValRows 
-		=	map {
-				my $attrs = $_->{attrs};
-				delete $_->{attrs};
-				$attrs;
-			}
-			@$valRows;
+	# store the attribute hashes individually
 	foreach my $id (@$groupIDs) {
-		my $attrs = shift @attrValRows;
+		my $attrs = shift @$attrValRows;
 		next if !defined $attrs;
 		return if !$self->setGroupAttrs($id, $attrs);
 	}
@@ -990,19 +951,21 @@ sub setGroupAttrs
 	my $groupID = shift;
 	my $attrs   = shift;
 
-	# we take the simple path and remove all attributes ...
+	# for now we take the simple path and remove all attributes ...
 	return if !$self->_doDelete('group_attr', [ $groupID ], 'group_id');
 
 	# ... and (re-)insert the given ones
-	foreach my $key (keys %$attrs) {
-		return if !$self->_doInsert(
-			'group_attr', [ {
-				group_id => $groupID,
-				name      => $key,
-				value     => $attrs->{$key},
-			} ]
-		);
-	}
+	my @attrData 
+		=	map {
+				{
+					group_id => $groupID,
+					name     => $_,
+					value    => $attrs->{$_},
+				}			
+			}
+			grep { defined $attrs->{$_} }
+			keys %$attrs;
+	return $self->_doInsert('group_attr', [ @attrData ]);
 	return 1;
 }
 
@@ -1089,16 +1052,6 @@ sub schemaFetchDBVersion
 	return $row->{schema_version};
 }
 
-sub schemaUpgradeDBFrom
-{
-	my $self        = shift;
-	my $currVersion = shift;
-
-	$self->_upgradeDBTo0_2() if $currVersion < 0.2;
-
-	return 1;
-}
-
 sub schemaSetDBVersion
 {
 	my $self      = shift;
@@ -1317,218 +1270,6 @@ sub schemaChangeColumns
 	return;
 }
 
-sub _upgradeDBTo0_2
-{
-	my $self = shift;
-
-	# move attributes into separate tables ...
-	#
-	# ... system attributes ...
-	$self->schemaAddTable(
-		'system_attr', 
-		[
-			'id:pk',
-			'system_id:fk',
-			'name:s.128',
-			'value:s.255',
-		]
-	);
-	foreach my $system ($self->fetchSystemByFilter()) {
-		my %attrs;
-		foreach my $key (keys %$system) {
-			next if substr($key, 0, 5) ne 'attr_';
-			my $attrValue = $system->{$key} || '';
-			next if $system->{id} > 0 && !length($attrValue);
-			my $newAttrName = substr($key, 5);
-			$attrs{$newAttrName} = $attrValue;
-		}
-		$self->setSystemAttrs($system->{id}, \%attrs);
-	}
-	$self->schemaDropColumns(
-		'system',
-		[
-			'attr_automnt_dir',
-			'attr_automnt_src',
-			'attr_country',
-			'attr_dm_allow_shutdown',
-			'attr_hw_graphic',
-			'attr_hw_monitor',
-			'attr_hw_mouse',
-			'attr_late_dm',
-			'attr_netbios_workgroup',
-			'attr_nis_domain',
-			'attr_nis_servers',
-			'attr_ramfs_fsmods',
-			'attr_ramfs_miscmods',
-			'attr_ramfs_nicmods',
-			'attr_ramfs_screen',
-			'attr_sane_scanner',
-			'attr_scratch',
-			'attr_slxgrp',
-			'attr_start_alsasound',
-			'attr_start_atd',
-			'attr_start_cron',
-			'attr_start_dreshal',
-			'attr_start_ntp',
-			'attr_start_nfsv4',
-			'attr_start_printer',
-			'attr_start_samba',
-			'attr_start_snmp',
-			'attr_start_sshd',
-			'attr_start_syslog',
-			'attr_start_x',
-			'attr_start_xdmcp',
-			'attr_tex_enable',
-			'attr_timezone',
-			'attr_tvout',
-			'attr_vmware',
-		],
-		[
-			'id:pk',
-			'export_id:fk',
-			'name:s.64',
-			'label:s.64',
-			'kernel:s.128',
-			'kernel_params:s.512',
-			'hidden:b',
-			'comment:s.1024',
-		]
-	);
-	#
-	# ... client attributes ...
-	$self->schemaAddTable(
-		'client_attr',
-		[
-			'id:pk',
-			'client_id:fk',
-			'name:s.128',
-			'value:s.255',
-		]
-	);
-	foreach my $client ($self->fetchClientByFilter()) {
-		my %attrs;
-		foreach my $key (keys %$client) {
-			next if substr($key, 0, 5) ne 'attr_';
-			my $attrValue = $client->{$key} || '';
-			next if !length($attrValue);
-			my $newAttrName = substr($key, 5);
-			$attrs{$newAttrName} = $attrValue;
-		}
-		$self->setClientAttrs($client->{id}, \%attrs);
-	}
-	$self->schemaDropColumns(
-		'client',
-		[
-			'attr_automnt_dir',
-			'attr_automnt_src',
-			'attr_country',
-			'attr_dm_allow_shutdown',
-			'attr_hw_graphic',
-			'attr_hw_monitor',
-			'attr_hw_mouse',
-			'attr_late_dm',
-			'attr_netbios_workgroup',
-			'attr_nis_domain',
-			'attr_nis_servers',
-			'attr_sane_scanner',
-			'attr_scratch',
-			'attr_slxgrp',
-			'attr_start_alsasound',
-			'attr_start_atd',
-			'attr_start_cron',
-			'attr_start_dreshal',
-			'attr_start_ntp',
-			'attr_start_nfsv4',
-			'attr_start_printer',
-			'attr_start_samba',
-			'attr_start_snmp',
-			'attr_start_sshd',
-			'attr_start_syslog',
-			'attr_start_x',
-			'attr_start_xdmcp',
-			'attr_tex_enable',
-			'attr_timezone',
-			'attr_tvout',
-			'attr_vmware',
-		],
-		[
-			'id:pk',
-			'name:s.128',
-			'mac:s.20',
-			'boot_type:s.20',
-			'unbootable:b',
-			'kernel_params:s.128',
-			'comment:s.1024',
-		]
-	);
-	#
-	# ... group attributes ...
-	$self->schemaAddTable(
-		'group_attr',
-		[
-			'id:pk',
-			'group_id:fk',
-			'name:s.128',
-			'value:s.255',
-		]
-	);
-	foreach my $group ($self->fetchGroupByFilter()) {
-		my %attrs;
-		foreach my $key (keys %$group) {
-			next if substr($key, 0, 5) ne 'attr_';
-			my $attrValue = $group->{$key} || '';
-			next if !length($attrValue);
-			my $newAttrName = substr($key, 5);
-			$attrs{$newAttrName} = $attrValue;
-		}
-		$self->setGroupAttrs($group->{id}, \%attrs);
-	}
-	$self->schemaDropColumns(
-		'groups',
-		[
-			'attr_automnt_dir',
-			'attr_automnt_src',
-			'attr_country',
-			'attr_dm_allow_shutdown',
-			'attr_hw_graphic',
-			'attr_hw_monitor',
-			'attr_hw_mouse',
-			'attr_late_dm',
-			'attr_netbios_workgroup',
-			'attr_nis_domain',
-			'attr_nis_servers',
-			'attr_sane_scanner',
-			'attr_scratch',
-			'attr_slxgrp',
-			'attr_start_alsasound',
-			'attr_start_atd',
-			'attr_start_cron',
-			'attr_start_dreshal',
-			'attr_start_ntp',
-			'attr_start_nfsv4',
-			'attr_start_printer',
-			'attr_start_samba',
-			'attr_start_snmp',
-			'attr_start_sshd',
-			'attr_start_syslog',
-			'attr_start_x',
-			'attr_start_xdmcp',
-			'attr_tex_enable',
-			'attr_timezone',
-			'attr_tvout',
-			'attr_vmware',
-		],
-		[
-			'id:pk',
-			'name:s.128',
-			'priority:i',
-			'comment:s.1024',
-		]
-	);
-
-	return 1;
-}
-
 1;
 
 =head1 NAME
diff --git a/config-db/slxconfig b/config-db/slxconfig
index 6df489ca..ce2a203c 100755
--- a/config-db/slxconfig
+++ b/config-db/slxconfig
@@ -23,6 +23,7 @@ slxconfig
 use Getopt::Long qw(:config pass_through);
 use List::Util qw(max);
 use Pod::Usage;
+use Storable qw(dclone);
 
 # add the folder this script lives in and the lib-folder to perl's
 # search path for modules:
@@ -34,6 +35,7 @@ use lib "$FindBin::RealBin/../config-db";
 
 # development path to config-db
 
+use OpenSLX::AttributeRoster;
 use OpenSLX::Basics;
 use OpenSLX::ConfigDB;
 use OpenSLX::ConfigFolder;
@@ -49,10 +51,9 @@ GetOptions(
 ) or pod2usage(2);
 pod2usage(-msg => $abstract, -verbose => 0, -exitval => 1) if $helpReq;
 if ($manReq) {
-	$ENV{LANG} = 'en_EN';
-
 	# avoid dubious problem with perldoc in combination with UTF-8 that
 	# leads to strange dashes and single-quotes being used
+	$ENV{LC_MESSAGES} = 'POSIX';
 	pod2usage(-verbose => 2);
 }
 if ($versionReq) {
@@ -90,6 +91,10 @@ elsif ($action =~ m[^change-s]i) {
 elsif ($action =~ m[^change-c]i) {
 	changeClientInConfigDB(@ARGV);
 }
+elsif ($action =~ m[^list-a]) {
+	print _tr("List of known attributes:\n");
+	listAttributes(@ARGV);
+}
 elsif ($action =~ m[^list-c]) {
 	print _tr("List of clients:\n");
 	listClients(@ARGV);
@@ -134,7 +139,7 @@ elsif ($action =~ m[^remove-c]i) {
 	removeClientFromConfigDB(@ARGV);
 }
 elsif ($action =~ m[^remove-g]i) {
-	removeClientFromConfigDB(@ARGV);
+	removeGroupFromConfigDB(@ARGV);
 }
 elsif ($action =~ m[^remove-s]i) {
 	removeSystemFromConfigDB(@ARGV);
@@ -150,6 +155,7 @@ else {
 			change-group
 			change-system
 			change-vendor-os
+			list-attributes
 			list-client
 			list-export
 			list-group
@@ -184,7 +190,7 @@ sub parseKeyValueArgs
 		}
 		my $key   = lc($1);
 		my $value = $2;
-		if ($value =~ m{^(?:UNDEF|NULL|-)$}) {
+		if ($value eq '-') {
 			$value = undef;
 		}
 		if (!grep { $_ eq $key } @$allowedKeys) {
@@ -212,7 +218,7 @@ sub parseKeyValueArgsWithAttrs
 		}
 		my $key   = lc($1);
 		my $value = $2;
-		if ($value =~ m{^(?:UNDEF|NULL|-)$}) {
+		if ($value eq '-') {
 			$value = undef;
 		}
 		if (grep { $_ eq $key } @$allowedKeys) {
@@ -224,7 +230,33 @@ sub parseKeyValueArgsWithAttrs
 		}
 	}
 
-	return (\%dataHash, \%attrHash);
+	if (wantarray) {
+		return (\%dataHash, \%attrHash);
+	}
+	else {
+		if (%attrHash) {
+			$dataHash{attrs} = \%attrHash;
+		}
+		return \%dataHash;
+	}
+}
+
+sub mergeNonExistingAttributes
+{
+	my $target = shift;
+	my $source = shift;
+
+	my $sourceAttrs = $source->{attrs} || {};
+
+	$target->{attrs} ||= {};
+	my $targetAttrs = $target->{attrs};
+
+	foreach my $key (keys %$sourceAttrs) {
+		next if exists $targetAttrs->{$key};
+		$targetAttrs->{$key} = $sourceAttrs->{$key};
+	}
+
+	return 1;
 }
 
 sub dumpElements
@@ -266,7 +298,11 @@ sub dumpElements
 				sort {
 					my $refCmp = ref($elem->{$a}) cmp ref($elem->{$b});
 					return $refCmp ? $refCmp : $a cmp $b;
-				} keys %$elem
+				} 
+				grep {
+					$_ ne 'name';
+				}
+				keys %$elem
 			);
 		}
 	}
@@ -277,6 +313,30 @@ sub dumpElements
 	return 1;
 }
 
+sub listAttributes
+{
+	my $name = shift;
+
+	# always set verbose in order to give descriptive info
+	$verbose = 1;
+
+	my $attrInfo = OpenSLX::AttributeRoster->getAttrInfo($name);
+	if (!defined $attrInfo) {
+		die _tr('attribute "%s" is unknown!', $name);
+	}
+	dumpElements(
+		'attribute', undef,
+		map {
+			my $attr = dclone($attrInfo->{$_});
+			$attr->{name} = $_;
+			$attr;
+		}
+		sort keys %$attrInfo
+	);
+
+	return 1;
+}
+
 sub listClients
 {
 	my $name = _cleanName(shift);
@@ -323,7 +383,7 @@ sub listGroups
 	}
 
 	dumpElements(
-		'groups', undef,
+		'group', undef,
 		map {
 			my @systemIDs = $openslxDB->fetchSystemIDsOfGroup($_->{id});
 			$_->{systems} 
@@ -440,7 +500,7 @@ sub listVendorOSes
 sub searchClients
 {
 	my @clientKeys = $openslxDB->getColumnsOfTable('client');
-	my @clientAttrKeys = $openslxDB->getKnownClientAttrs();
+	my @clientAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
 	my ($clientData, $clientAttrs) = parseKeyValueArgsWithAttrs(
 		\@clientKeys, \@clientAttrKeys, 'client', @_
 	);
@@ -471,7 +531,7 @@ sub searchClients
 sub searchGroups
 {
 	my @groupKeys = $openslxDB->getColumnsOfTable('groups');
-	my @groupAttrKeys = $openslxDB->getKnownClientAttrs();
+	my @groupAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
 	my ($groupData, $groupAttrs) = parseKeyValueArgsWithAttrs(
 		\@groupKeys, \@groupAttrKeys, 'group', @_
 	);
@@ -537,7 +597,7 @@ sub searchExports
 sub searchSystems
 {
 	my @systemKeys = $openslxDB->getColumnsOfTable('system');
-	my @systemAttrKeys = $openslxDB->getKnownSystemAttrs();
+	my @systemAttrKeys = OpenSLX::AttributeRoster->getSystemAttrs();
 	my ($systemData, $systemAttrs) = parseKeyValueArgsWithAttrs(
 		\@systemKeys, \@systemAttrKeys, 'system', @_
 	);
@@ -651,7 +711,10 @@ sub addClientToConfigDB
 
 	my @clientKeys = $openslxDB->getColumnsOfTable('client');
 	push @clientKeys, 'systems';
-	my $clientData = parseKeyValueArgs(\@clientKeys, 'client', @_);
+	my @clientAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
+	my $clientData = parseKeyValueArgsWithAttrs(
+		\@clientKeys, \@clientAttrKeys, 'client', @_
+	);
 	$clientData->{name} = $clientName;
 
 	my @systemIDs;
@@ -709,14 +772,16 @@ sub addClientToConfigDB
 sub addGroupToConfigDB
 {
 	my $groupName = _cleanName(shift || '');
-
 	if (!length($groupName)) {
 		die _tr("you have to specify the name for the new group\n");
 	}
 
 	my @groupKeys = $openslxDB->getColumnsOfTable('groups');
 	push @groupKeys, 'systems', 'clients';
-	my $groupData = parseKeyValueArgs(\@groupKeys, 'groups', @_);
+	my @groupAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
+	my $groupData = parseKeyValueArgsWithAttrs(
+		\@groupKeys, \@groupAttrKeys, 'group', @_
+	);
 	$groupData->{name} = $groupName;
 
 	my @systemIDs;
@@ -784,8 +849,12 @@ sub addSystemToConfigDB
 
 	my @systemKeys = $openslxDB->getColumnsOfTable('system');
 	push @systemKeys, 'clients', 'export';
-	my $systemData = parseKeyValueArgs(\@systemKeys, 'system', @_);
+	my @systemAttrKeys = OpenSLX::AttributeRoster->getSystemAttrs();
+	my $systemData = parseKeyValueArgsWithAttrs(
+		\@systemKeys, \@systemAttrKeys, 'system', @_
+	);
 	$systemData->{name} = $systemName;
+	$systemData->{attrs} ||= {};
 
 	my $exportName = $systemData->{export} || '';
 	delete $systemData->{export};
@@ -827,21 +896,19 @@ sub addSystemToConfigDB
 			$systemName);
 	}
 
+	# activate kdm and X if system is based on kde:
 	if ($systemName =~ m[\bkde\b]) {
-
-		# activate kdm and X if system is based on kde:
-		$systemData->{attr_start_xdmcp} = 'kdm'
-			unless exists $systemData->{attr_start_xdmcp};
-		$systemData->{attr_start_x} = 'yes'
-			unless exists $systemData->{attr_start_x};
+		$systemData->{attrs}->{start_xdmcp} = 'kdm'
+			unless exists $systemData->{attrs}->{start_xdmcp};
+		$systemData->{attrs}->{start_x} = 'yes'
+			unless exists $systemData->{attrs}->{start_x};
 	}
+	# activate gdm and X if system is based on GNOME:
 	if ($systemName =~ m[\bgnome\b]) {
-
-		# activate gdm and X if system is based on GNOME:
-		$systemData->{attr_start_xdmcp} = 'gdm'
-			unless exists $systemData->{attr_start_xdmcp};
-		$systemData->{attr_start_x} = 'yes'
-			unless exists $systemData->{attr_start_x};
+		$systemData->{attrs}->{start_xdmcp} = 'gdm'
+			unless exists $systemData->{attrs}->{start_xdmcp};
+		$systemData->{attrs}->{start_x} = 'yes'
+			unless exists $systemData->{attrs}->{start_x};
 	}
 
 	my $systemConfigPath =
@@ -882,7 +949,10 @@ sub changeClientInConfigDB
 
 	my @clientKeys = $openslxDB->getColumnsOfTable('client');
 	push @clientKeys, 'systems', 'add-systems', 'remove-systems';
-	my $clientData = parseKeyValueArgs(\@clientKeys, 'client', @_);
+	my @clientAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
+	my $clientData = parseKeyValueArgsWithAttrs(
+		\@clientKeys, \@clientAttrKeys, 'client', @_
+	);
 
 	my $client = $openslxDB->fetchClientByFilter({'name' => $clientName});
 	if (!defined $client) {
@@ -966,7 +1036,10 @@ sub changeGroupInConfigDB
 	push @groupKeys, qw(
 		systems add-systems remove-systems clients add-clients remove-clients
 	);
-	my $groupData = parseKeyValueArgs(\@groupKeys, 'group', @_);
+	my @groupAttrKeys = OpenSLX::AttributeRoster->getClientAttrs();
+	my $groupData = parseKeyValueArgsWithAttrs(
+		\@groupKeys, \@groupAttrKeys, 'group', @_
+	);
 
 	my $group = $openslxDB->fetchGroupByFilter({'name' => $groupName});
 	if (!defined $group) {
@@ -974,6 +1047,8 @@ sub changeGroupInConfigDB
 			$groupName);
 	}
 
+	mergeNonExistingAttributes($groupData, $group);
+
 	my (@systemIDs, @clientIDs);
 	if (exists $groupData->{systems}) {
 		@systemIDs = map {
@@ -1077,7 +1152,10 @@ sub changeSystemInConfigDB
 
 	my @systemKeys = $openslxDB->getColumnsOfTable('system');
 	push @systemKeys, 'clients', 'add-clients', 'remove-clients';
-	my $systemData = parseKeyValueArgs(\@systemKeys, 'system', @_);
+	my @systemAttrKeys = OpenSLX::AttributeRoster->getSystemAttrs();
+	my $systemData = parseKeyValueArgsWithAttrs(
+		\@systemKeys, \@systemAttrKeys, 'system', @_
+	);
 
 	my $system = $openslxDB->fetchSystemByFilter({'name' => $systemName});
 	if (!defined $system) {
@@ -1166,7 +1244,7 @@ sub removeClientFromConfigDB
 	return 1;
 }
 
-sub removegroupFromConfigDB
+sub removeGroupFromConfigDB
 {
 	my $groupName = _cleanName(shift || '');
 
@@ -1176,7 +1254,7 @@ sub removegroupFromConfigDB
 		);
 	}
 
-	my $groupData = parseKeyValueArgs(['name'], 'groups', @_);
+	my $groupData = parseKeyValueArgs(['name'], 'group', @_);
 
 	my $group = $openslxDB->fetchGroupByFilter({'name' => $groupName});
 	if (!defined $group) {
@@ -1268,7 +1346,7 @@ adds a new group to the config-DB
 
 =item B<<     change-vendor-os <vendor-os-name> [<key>=<value> ...] >>
 
-changes the data of an existing vendor-OS in the config-DB
+changes the data of an existing vendor-OS in the config-DB.
 
 =item B<<     change-export <export-name> [<key>=<value> ...] >>
 
@@ -1278,14 +1356,27 @@ changes the data of an existing export in the config-DB
 
 changes the data of an existing client in the config-DB
 
+Note: you can use the special value '-' to unset a key (mostly useful
+for attributes).
+
 =item B<<     change-group <group-name> [<key>=<value> ...] >>
 
 changes the data of an existing group in the config-DB
 
+Note: you can use the special value '-' to unset a key (mostly useful
+for attributes).
+
 =item B<<     change-system <system-name> [<key>=<value> ...] >>
 
 changes the data of an existing system in the config-DB
 
+Note: you can use the special value '-' to unset a key (mostly useful
+for attributes).
+
+=item B<<     list-attributes [<attr-name>] >>
+
+lists all attributes or the one with the given name
+
 =item B<<     list-client [<client-name>] >>
 
 lists client with given name
@@ -1389,6 +1480,16 @@ lists all existing instances of the respective DB-objects.
 
 =back
 
+=head3 Listing known attributes
+
+=over 8
+
+=item B<<     slxconfig list-attr >>
+
+lists all known attributes (--verbose will give details).
+
+=back
+
 =head3 Adding a new System to an exported Vendor-OS
 
 =over 8
@@ -1426,7 +1527,7 @@ associated with this client, yet (so it can't boot anything).
 
 =item B<<                          systems=suse-10.1,debian-4.0 \ >>
 
-=item B<<                          attr_start_x=no >>
+=item B<<                          start_x=no >>
 
 adds a new client named 'vmware-1', being identified by the MAC
 '01:02:03:04:05:06' to the config-DB. The systems 'suse-10.1' &
@@ -1442,10 +1543,11 @@ During boot, the X-server will not be started by this client
 
 =over 8
 
-=item B<<     slxconfig change-system suse-10.1 attr_start_xdmcp=gnome >>
+=item B<<     slxconfig change-system suse-10.1 start_xdmcp=gnome vmware=- >>
 
 will change the system named 'suse-10.1' such that it will use
-the GNOME session manager.
+the GNOME session manager. The attribute vmware is set to undefined (such that
+it will be inherited from the default system)
 
 =item B<<     slxconfig change-system suse-10.1 add-clients=vmware-1 >>
 
@@ -1463,7 +1565,7 @@ will remove the client 'vmware-1' from the system named
 
 =over 8
 
-=item B<<     slxconfig change-client PC131 attr_start_snmp=yes >>
+=item B<<     slxconfig change-client PC131 start_snmp=yes >>
 
 will change the client named 'PC131' such that it will start
 the SNMP daemon on all systems that it boots.
diff --git a/config-db/slxconfig-demuxer b/config-db/slxconfig-demuxer
index c71be64d..5019cab9 100755
--- a/config-db/slxconfig-demuxer
+++ b/config-db/slxconfig-demuxer
@@ -75,6 +75,10 @@ my (
 	$versionReq,
 );
 
+if ($> != 0) {
+	die _tr("Sorry, this script can only be executed by the superuser!\n");
+}
+
 GetOptions(
 	'dhcp-export-type=s' => \$dhcpType,
 	'dry-run'            => \$dryRun,
@@ -85,9 +89,9 @@ GetOptions(
   or pod2usage(2);
 pod2usage(-msg => $abstract, -verbose => 0, -exitval => 1) if $helpReq;
 if ($manReq) {
-	$ENV{LANG} = 'en_EN';
 	# avoid dubious problem with perldoc in combination with UTF-8 that
 	# leads to strange dashes and single-quotes being used
+	$ENV{LC_MESSAGES} = 'POSIX';
 	pod2usage(-verbose => 2);
 }
 if ($versionReq) {
@@ -120,7 +124,7 @@ if (createConfigFolderForDefaultSystem()) {
 my $lockFile = "$openslxConfig{'private-path'}/config-demuxer.lock";
 lockScript($lockFile);
 
-END { unlockScript($lockFile); }
+END { unlockScript($lockFile) if defined $lockFile; }
 
 my $tempPath = "$openslxConfig{'temp-path'}/slxconfig-demuxer";
 if (!$dryRun) {
@@ -217,16 +221,15 @@ sub folderContainsFiles
 sub digestAttributes
 {    # returns a digest-string for the given attribute hash, in order to
 	    # facilitate comparing different attribute hashes.
-	my $attrs = shift;
+	my $object = shift;
 
+	my $attrs = $object->{attrs} || {};
 	my $attrsAsString 
-		=   join ';', 
-			map { 
-				my $val = $attrs->{$_} || '';
-				"$_=$val";
-			}
-		    sort { $a cmp $b }
-		    grep { isAttribute($_) } keys %$attrs;
+		=	join ';', 
+			map { "$_=$attrs->{$_}" }
+			sort
+			grep { defined $attrs->{$_} } 
+			keys %$attrs;
 
 	vlog(3, "Attribute-string: $attrsAsString");
 	use Digest::MD5 qw(md5_hex);
@@ -235,19 +238,15 @@ sub digestAttributes
 
 sub writeAttributesToFile
 {
-	my $attrHash          = shift;
+	my $object            = shift;
 	my $fileName          = shift;
-	my $grepForAttributes = shift;
 
 	return if $dryRun;
 
 	my $content = "# attributes set by slxconfig-demuxer:\n";
-	my @attrs 
-		= $grepForAttributes
-			? grep { isAttribute($_) } sort keys %$attrHash
-			: sort keys %$attrHash;
-	foreach my $attr (@attrs) {
-		my $attrVal = $attrHash->{$attr} || '';
+	my $attrs = $object->{attrs} || {};
+	foreach my $attr (sort keys %$attrs) {
+		my $attrVal = $attrs->{$attr} || '';
 		if (length($attrVal) > 0) {
 			my $externalAttrName = externalAttrName($attr);
 			$content .= qq[$externalAttrName="$attrVal"\n];
@@ -449,13 +448,15 @@ sub generateInitalRamFS
 	# generate initramfs-setup file (with settings relevant for initramfs only):
 	my $initramfsAttrFile = "$tempPath/initramfs-setup";
 	my $initramfsAttrs    = {
-		'host_name'		=> 'slx-client', # silly default just to have something
-		'ramfs_fsmods'  => $info->{'attr_ramfs_fsmods'} || '',
-		'ramfs_nicmods' => $info->{'attr_ramfs_nicmods'} || '',
-		'ramfs_screen'  => $info->{'attr_ramfs_screen'} || '',
-		'rootfs'        => $info->{'export-uri'} || '',
+		attrs => {
+			'host_name'		=> 'slx-client', # just to have something at all
+			'ramfs_fsmods'  => $info->{'attr_ramfs_fsmods'} || '',
+			'ramfs_nicmods' => $info->{'attr_ramfs_nicmods'} || '',
+			'ramfs_screen'  => $info->{'attr_ramfs_screen'} || '',
+			'rootfs'        => $info->{'export-uri'} || '',
+		},
 	};
-	writeAttributesToFile($initramfsAttrs, $initramfsAttrFile, 0);
+	writeAttributesToFile($initramfsAttrs, $initramfsAttrFile);
 	# and pass the generated initramfs-setup file to mkdxsinitrd:
 	$cmd .= "-c $initramfsAttrFile ";
 
@@ -502,7 +503,7 @@ sub writeSystemPXEFiles
 sub writeDhcpConfig
 {
 	vlog(0, _tr("sorry, exporting dhcp data is not implemented yet!"));
-	my $dhcpModule = "OpenSLX::Export::DHCP::$dhcpType";
+	my $dhcpModule = "OpenSLX::ConfigExport::DHCP::$dhcpType";
 	if (!eval { require $dhcpModule } ) {
 		die _tr("unable to load DHCP-Export backend '%s'! (%s)\n",
 			$dhcpModule, $@);
@@ -562,7 +563,7 @@ sub writeClientConfigurationsForSystem
 			copyExternalSystemConfig($externalSystemID, $buildPath,
 				$externalClientName);
 
-			writeAttributesToFile($client, $attrFile, 1);
+			writeAttributesToFile($client, $attrFile);
 
 			# create tar containing external system configuration
 			# and client attribute file, this time referring to the client
@@ -649,7 +650,7 @@ sub writeSystemConfiguration
 		)
 	);
 	my $attrFile = "$buildPath/initramfs/machine-setup";
-	writeAttributesToFile($info, $attrFile, 1);
+	writeAttributesToFile($info, $attrFile);
 	
 	writePluginConfigurationsForSystem($info, $buildPath);
 
diff --git a/config-db/t/12-system.t b/config-db/t/12-system.t
index 7a3e5e1e..dc8670de 100644
--- a/config-db/t/12-system.t
+++ b/config-db/t/12-system.t
@@ -368,6 +368,33 @@ is($system1->{name}, q{SYS-'1'}, q{really got system named "SYS-'1'"});
 # changing nothing at all should succeed
 ok($configDB->changeSystem(1), 'changing nothing at all in system 1');
 
+# adding attributes should work
+$inSystem1->{attrs}->{slxgrp} = 'slxgrp1';
+$inSystem1->{attrs}->{vmware} = 'yes';
+ok($configDB->changeSystem(1, $inSystem1), 'adding attrs to system 1');
+$system1 = $configDB->fetchSystemByID(1);
+is($system1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($system1->{attrs}->{vmware}, 'yes', 'attr vmware has correct value');
+
+# changing an attribute should work
+$inSystem1->{attrs}->{vmware} = 'no';
+ok($configDB->changeSystem(1, $inSystem1), 'changing vmware in system 1');
+$system1 = $configDB->fetchSystemByID(1);
+is($system1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($system1->{attrs}->{vmware}, 'no', 'attr vmware has correct value');
+
+# deleting an attribute should remove it
+delete $inSystem1->{attrs}->{slxgrp};
+ok($configDB->changeSystem(1, $inSystem1), 'changing slxgrp in system 1');
+$system1 = $configDB->fetchSystemByID(1);
+ok(!exists $system1->{attrs}->{slxgrp}, 'attr slxgrp should be gone');
+
+# undef'ing an attribute should remove it, too
+$inSystem1->{attrs}->{vmware} = undef;
+ok($configDB->changeSystem(1, $inSystem1), 'undefining vmware in system 1');
+$system1 = $configDB->fetchSystemByID(1);
+ok(!exists $system1->{attrs}->{vmware}, 'attr vmware should be gone');
+
 # changing a non-existing column should fail
 ok(
 	! eval { $configDB->changeSystem(1, { xname => "xx" }) }, 
diff --git a/config-db/t/13-client.t b/config-db/t/13-client.t
index 5848ba53..1c8ea99f 100644
--- a/config-db/t/13-client.t
+++ b/config-db/t/13-client.t
@@ -357,6 +357,33 @@ is($client1->{name}, q{CLI-'1'}, q{really got client named "CLI-'1'"});
 # changing nothing at all should succeed
 ok($configDB->changeClient(1), 'changing nothing at all in client 1');
 
+# adding attributes should work
+$inClient1->{attrs}->{slxgrp} = 'slxgrp1';
+$inClient1->{attrs}->{vmware} = 'yes';
+ok($configDB->changeClient(1, $inClient1), 'adding attrs to client 1');
+$client1 = $configDB->fetchClientByID(1);
+is($client1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($client1->{attrs}->{vmware}, 'yes', 'attr vmware has correct value');
+
+# changing an attribute should work
+$inClient1->{attrs}->{vmware} = 'no';
+ok($configDB->changeClient(1, $inClient1), 'changing vmware in client 1');
+$client1 = $configDB->fetchClientByID(1);
+is($client1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($client1->{attrs}->{vmware}, 'no', 'attr vmware has correct value');
+
+# deleting an attribute should remove it
+delete $inClient1->{attrs}->{slxgrp};
+ok($configDB->changeClient(1, $inClient1), 'changing slxgrp in client 1');
+$client1 = $configDB->fetchClientByID(1);
+ok(!exists $client1->{attrs}->{slxgrp}, 'attr slxgrp should be gone');
+
+# undef'ing an attribute should remove it, too
+$inClient1->{attrs}->{vmware} = undef;
+ok($configDB->changeClient(1, $inClient1), 'undefining vmware in client 1');
+$client1 = $configDB->fetchClientByID(1);
+ok(!exists $client1->{attrs}->{vmware}, 'attr vmware should be gone');
+
 # changing a non-existing column should fail
 ok(
 	! eval { $configDB->changeClient(1, { xname => "xx" }) }, 
diff --git a/config-db/t/14-group.t b/config-db/t/14-group.t
index 59530257..b06620ce 100644
--- a/config-db/t/14-group.t
+++ b/config-db/t/14-group.t
@@ -339,6 +339,33 @@ is($group1->{name}, q{GRP-'1'}, q{really got group named "GRP-'1'"});
 # changing nothing at all should succeed
 ok($configDB->changeGroup(1), 'changing nothing at all in group 1');
 
+# adding attributes should work
+$inGroup1->{attrs}->{slxgrp} = 'slxgrp1';
+$inGroup1->{attrs}->{vmware} = 'yes';
+ok($configDB->changeGroup(1, $inGroup1), 'adding attrs to group 1');
+$group1 = $configDB->fetchGroupByID(1);
+is($group1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($group1->{attrs}->{vmware}, 'yes', 'attr vmware has correct value');
+
+# changing an attribute should work
+$inGroup1->{attrs}->{vmware} = 'no';
+ok($configDB->changeGroup(1, $inGroup1), 'changing vmware in group 1');
+$group1 = $configDB->fetchGroupByID(1);
+is($group1->{attrs}->{slxgrp}, 'slxgrp1', 'attr slxgrp has correct value');
+is($group1->{attrs}->{vmware}, 'no', 'attr vmware has correct value');
+
+# deleting an attribute should remove it
+delete $inGroup1->{attrs}->{slxgrp};
+ok($configDB->changeGroup(1, $inGroup1), 'changing slxgrp in group 1');
+$group1 = $configDB->fetchGroupByID(1);
+ok(!exists $group1->{attrs}->{slxgrp}, 'attr slxgrp should be gone');
+
+# undef'ing an attribute should remove it, too
+$inGroup1->{attrs}->{vmware} = undef;
+ok($configDB->changeGroup(1, $inGroup1), 'undefining vmware in group 1');
+$group1 = $configDB->fetchGroupByID(1);
+ok(!exists $group1->{attrs}->{vmware}, 'attr vmware should be gone');
+
 # changing a non-existing column should fail
 ok(
 	! eval { $configDB->changeGroup(1, { xname => "xx" }) }, 
diff --git a/config-db/t/25-attributes.t b/config-db/t/25-attributes.t
index ce83d037..0a83afa9 100644
--- a/config-db/t/25-attributes.t
+++ b/config-db/t/25-attributes.t
@@ -5,6 +5,8 @@ use warnings;
 
 use lib '/opt/openslx/lib';
 
+use Storable qw(dclone);
+
 # basic init
 use OpenSLX::ConfigDB qw(:support);
 
@@ -12,25 +14,25 @@ my $configDB = OpenSLX::ConfigDB->new;
 $configDB->connect();
 
 my $defaultAttrs = {	# mostly copied from DBSchema
-	'ramfs_fsmods' => '',
-	'ramfs_miscmods' => '',
+	'ramfs_fsmods' => undef,
+	'ramfs_miscmods' => undef,
 	'ramfs_nicmods' => 'forcedeth e1000 e100 tg3 via-rhine r8169 pcnet32',
-	'ramfs_screen' => '',
+	'ramfs_screen' => undef,
 
-	'automnt_dir' => '',
-	'automnt_src' => '',
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
 	'country' => 'de',
 	'dm_allow_shutdown' => 'user',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
 	'late_dm' => 'no',
 	'netbios_workgroup' => 'slx-network',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
-	'scratch' => '',
-	'slxgrp' => '',
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
+	'scratch' => undef,
+	'slxgrp' => undef,
 	'start_alsasound' => 'yes',
 	'start_atd' => 'no',
 	'start_cron' => 'no',
@@ -128,24 +130,24 @@ ok(
 # default client attributes:
 my $shouldBeAttrs1 = {
 	'ramfs_fsmods' => 'squashfs',
-	'ramfs_miscmods' => '',
+	'ramfs_miscmods' => undef,
 	'ramfs_nicmods' => 'forcedeth e1000 r8169',
-	'ramfs_screen' => '',
+	'ramfs_screen' => undef,
 
-	'automnt_dir' => '',
-	'automnt_src' => '',
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
 	'country' => 'de',
 	'dm_allow_shutdown' => 'user',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
 	'late_dm' => 'no',
 	'netbios_workgroup' => 'slx-network',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
-	'scratch' => '',
-	'slxgrp' => '',
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
+	'scratch' => undef,
+	'slxgrp' => undef,
 	'start_alsasound' => 'yes',
 	'start_atd' => 'no',
 	'start_cron' => 'no',
@@ -272,45 +274,45 @@ ok(
 );
 
 # check merging of attributes into client, the order should be:
-# default client attributes overruled by group attributes (ordererd by priority) 
+# default client attributes overruled by group attributes (ordered by priority) 
 # overruled by specific client attributes:
 $shouldBeAttrs1 = {
-	'ramfs_fsmods' => '',
-	'ramfs_miscmods' => '',
-	'ramfs_nicmods' => '',
-	'ramfs_screen' => '',
-
-	'automnt_dir' => '',
-	'automnt_src' => '',
-	'country' => '',
-	'dm_allow_shutdown' => '',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
-	'late_dm' => '',
-	'netbios_workgroup' => '',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
+	'ramfs_fsmods' => undef,
+	'ramfs_miscmods' => undef,
+	'ramfs_nicmods' => undef,
+	'ramfs_screen' => undef,
+
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
+	'country' => undef,
+	'dm_allow_shutdown' => undef,
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
+	'late_dm' => undef,
+	'netbios_workgroup' => undef,
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
 	'scratch' => '/dev/sdx3',
-	'slxgrp' => '',
-	'start_alsasound' => '',
-	'start_atd' => '',
-	'start_cron' => '',
-	'start_dreshal' => '',
-	'start_ntp' => '',
-	'start_nfsv4' => '',
-	'start_printer' => '',
-	'start_samba' => '',
+	'slxgrp' => undef,
+	'start_alsasound' => undef,
+	'start_atd' => undef,
+	'start_cron' => undef,
+	'start_dreshal' => undef,
+	'start_ntp' => undef,
+	'start_nfsv4' => undef,
+	'start_printer' => undef,
+	'start_samba' => undef,
 	'start_snmp' => 'yes',
-	'start_sshd' => '',
-	'start_syslog' => '',
-	'start_x' => '',
-	'start_xdmcp' => '',
-	'tex_enable' => '',
+	'start_sshd' => undef,
+	'start_syslog' => undef,
+	'start_x' => undef,
+	'start_xdmcp' => undef,
+	'tex_enable' => undef,
 	'timezone' => 'America/New_York',
-	'tvout' => '',
-	'vmware' => '',
+	'tvout' => undef,
+	'vmware' => undef,
 };
 my $mergedClient1 = $configDB->fetchClientByID(1);
 ok(
@@ -319,48 +321,48 @@ ok(
 );
 foreach my $key (sort keys %$shouldBeAttrs1) {
 	is(
-		$mergedClient1->{attrs}->{$key} || '', $shouldBeAttrs1->{$key} || '', 
+		$mergedClient1->{attrs}->{$key}, $shouldBeAttrs1->{$key}, 
 		"checking merged attribute $key for client 1"
 	);
 }
 
 $shouldBeAttrs3 = {
-	'ramfs_fsmods' => '',
-	'ramfs_miscmods' => '',
-	'ramfs_nicmods' => '',
-	'ramfs_screen' => '',
-
-	'automnt_dir' => '',
-	'automnt_src' => '',
-	'country' => '',
-	'dm_allow_shutdown' => '',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
-	'late_dm' => '',
-	'netbios_workgroup' => '',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
-	'scratch' => '',
-	'slxgrp' => '',
-	'start_alsasound' => '',
-	'start_atd' => '',
-	'start_cron' => '',
-	'start_dreshal' => '',
-	'start_ntp' => '',
-	'start_nfsv4' => '',
-	'start_printer' => '',
-	'start_samba' => '',
+	'ramfs_fsmods' => undef,
+	'ramfs_miscmods' => undef,
+	'ramfs_nicmods' => undef,
+	'ramfs_screen' => undef,
+
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
+	'country' => undef,
+	'dm_allow_shutdown' => undef,
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
+	'late_dm' => undef,
+	'netbios_workgroup' => undef,
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
+	'scratch' => undef,
+	'slxgrp' => undef,
+	'start_alsasound' => undef,
+	'start_atd' => undef,
+	'start_cron' => undef,
+	'start_dreshal' => undef,
+	'start_ntp' => undef,
+	'start_nfsv4' => undef,
+	'start_printer' => undef,
+	'start_samba' => undef,
 	'start_snmp' => 'yes',
-	'start_sshd' => '',
-	'start_syslog' => '',
-	'start_x' => '',
-	'start_xdmcp' => '',
-	'tex_enable' => '',
+	'start_sshd' => undef,
+	'start_syslog' => undef,
+	'start_x' => undef,
+	'start_xdmcp' => undef,
+	'tex_enable' => undef,
 	'timezone' => 'Europe/London',
-	'tvout' => '',
-	'vmware' => '',
+	'tvout' => undef,
+	'vmware' => undef,
 };
 
 # remove all attributes from client 3
@@ -373,7 +375,7 @@ ok(
 );
 foreach my $key (sort keys %$shouldBeAttrs1) {
 	is(
-		$mergedClient3->{attrs}->{$key} || '', $shouldBeAttrs3->{$key} || '', 
+		$mergedClient3->{attrs}->{$key}, $shouldBeAttrs3->{$key}, 
 		"checking merged attribute $key for client 3"
 	);
 }
@@ -384,41 +386,41 @@ ok(
 	'group-IDs of default client have been set'
 );
 $shouldBeAttrs1 = {
-	'ramfs_fsmods' => '',
-	'ramfs_miscmods' => '',
-	'ramfs_nicmods' => '',
-	'ramfs_screen' => '',
-
-	'automnt_dir' => '',
-	'automnt_src' => '',
-	'country' => '',
-	'dm_allow_shutdown' => '',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
-	'late_dm' => '',
-	'netbios_workgroup' => '',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
+	'ramfs_fsmods' => undef,
+	'ramfs_miscmods' => undef,
+	'ramfs_nicmods' => undef,
+	'ramfs_screen' => undef,
+
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
+	'country' => undef,
+	'dm_allow_shutdown' => undef,
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
+	'late_dm' => undef,
+	'netbios_workgroup' => undef,
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
 	'scratch' => '/dev/sdx3',
-	'slxgrp' => '',
-	'start_alsasound' => '',
-	'start_atd' => '',
-	'start_cron' => '',
-	'start_dreshal' => '',
-	'start_ntp' => '',
-	'start_nfsv4' => '',
-	'start_printer' => '',
-	'start_samba' => '',
+	'slxgrp' => undef,
+	'start_alsasound' => undef,
+	'start_atd' => undef,
+	'start_cron' => undef,
+	'start_dreshal' => undef,
+	'start_ntp' => undef,
+	'start_nfsv4' => undef,
+	'start_printer' => undef,
+	'start_samba' => undef,
 	'start_snmp' => 'yes',
-	'start_sshd' => '',
-	'start_syslog' => '',
-	'start_x' => '',
-	'start_xdmcp' => '',
-	'tex_enable' => '',
+	'start_sshd' => undef,
+	'start_syslog' => undef,
+	'start_x' => undef,
+	'start_xdmcp' => undef,
+	'tex_enable' => undef,
 	'timezone' => 'America/New_York',
-	'tvout' => '',
+	'tvout' => undef,
 	'vmware' => 'yes',
 };
 $mergedClient1 = $configDB->fetchClientByID(1);
@@ -428,47 +430,47 @@ ok(
 );
 foreach my $key (sort keys %$shouldBeAttrs1) {
 	is(
-		$mergedClient1->{attrs}->{$key} || '', $shouldBeAttrs1->{$key} || '', 
+		$mergedClient1->{attrs}->{$key}, $shouldBeAttrs1->{$key}, 
 		"checking merged attribute $key for client 1"
 	);
 }
 
 $shouldBeAttrs3 = {
-	'ramfs_fsmods' => '',
-	'ramfs_miscmods' => '',
-	'ramfs_nicmods' => '',
-	'ramfs_screen' => '',
-
-	'automnt_dir' => '',
-	'automnt_src' => '',
-	'country' => '',
-	'dm_allow_shutdown' => '',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
-	'late_dm' => '',
-	'netbios_workgroup' => '',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
+	'ramfs_fsmods' => undef,
+	'ramfs_miscmods' => undef,
+	'ramfs_nicmods' => undef,
+	'ramfs_screen' => undef,
+
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
+	'country' => undef,
+	'dm_allow_shutdown' => undef,
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
+	'late_dm' => undef,
+	'netbios_workgroup' => undef,
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
 	'scratch' => '/dev/hdd1',
-	'slxgrp' => '',
-	'start_alsasound' => '',
-	'start_atd' => '',
-	'start_cron' => '',
-	'start_dreshal' => '',
-	'start_ntp' => '',
-	'start_nfsv4' => '',
-	'start_printer' => '',
-	'start_samba' => '',
+	'slxgrp' => undef,
+	'start_alsasound' => undef,
+	'start_atd' => undef,
+	'start_cron' => undef,
+	'start_dreshal' => undef,
+	'start_ntp' => undef,
+	'start_nfsv4' => undef,
+	'start_printer' => undef,
+	'start_samba' => undef,
 	'start_snmp' => 'yes',
-	'start_sshd' => '',
-	'start_syslog' => '',
-	'start_x' => '',
-	'start_xdmcp' => '',
-	'tex_enable' => '',
+	'start_sshd' => undef,
+	'start_syslog' => undef,
+	'start_x' => undef,
+	'start_xdmcp' => undef,
+	'tex_enable' => undef,
 	'timezone' => 'Europe/London',
-	'tvout' => '',
+	'tvout' => undef,
 	'vmware' => 'yes',
 };
 $mergedClient3 = $configDB->fetchClientByID(3);
@@ -478,37 +480,37 @@ ok(
 );
 foreach my $key (sort keys %$shouldBeAttrs1) {
 	is(
-		$mergedClient3->{attrs}->{$key} || '', $shouldBeAttrs3->{$key} || '', 
+		$mergedClient3->{attrs}->{$key}, $shouldBeAttrs3->{$key}, 
 		"checking merged attribute $key for client 3"
 	);
 }
 
 # finally we merge systems into clients and check the outcome of that
-my $fullMerge11 = { %$mergedClient1 };
+my $fullMerge11 = dclone($mergedClient1);
 ok(
 	mergeAttributes($fullMerge11, $mergedSystem1),
 	'merging system 1 into client 1'
 );
 my $shouldBeAttrs11 = {
 	'ramfs_fsmods' => 'squashfs',
-	'ramfs_miscmods' => '',
+	'ramfs_miscmods' => undef,
 	'ramfs_nicmods' => 'forcedeth e1000 r8169',
-	'ramfs_screen' => '',
+	'ramfs_screen' => undef,
 
-	'automnt_dir' => '',
-	'automnt_src' => '',
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
 	'country' => 'de',
 	'dm_allow_shutdown' => 'user',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
 	'late_dm' => 'no',
 	'netbios_workgroup' => 'slx-network',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
 	'scratch' => '/dev/sdx3',
-	'slxgrp' => '',
+	'slxgrp' => undef,
 	'start_alsasound' => 'yes',
 	'start_atd' => 'no',
 	'start_cron' => 'no',
@@ -529,36 +531,36 @@ my $shouldBeAttrs11 = {
 };
 foreach my $key (sort keys %$shouldBeAttrs11) {
 	is(
-		$fullMerge11->{attrs}->{$key} || '', $shouldBeAttrs11->{$key} || '', 
+		$fullMerge11->{attrs}->{$key}, $shouldBeAttrs11->{$key}, 
 		"checking merged attribute $key for client 1 / system 1"
 	);
 }
 
-my $fullMerge31 = { %$mergedClient3 };
+my $fullMerge31 = dclone($mergedClient3);
 ok(
 	mergeAttributes($fullMerge31, $mergedSystem1),
 	'merging system 1 into client 3'
 );
 my $shouldBeAttrs31 = {
 	'ramfs_fsmods' => 'squashfs',
-	'ramfs_miscmods' => '',
+	'ramfs_miscmods' => undef,
 	'ramfs_nicmods' => 'forcedeth e1000 r8169',
-	'ramfs_screen' => '',
+	'ramfs_screen' => undef,
 
-	'automnt_dir' => '',
-	'automnt_src' => '',
+	'automnt_dir' => undef,
+	'automnt_src' => undef,
 	'country' => 'de',
 	'dm_allow_shutdown' => 'user',
-	'hw_graphic' => '',
-	'hw_monitor' => '',
-	'hw_mouse' => '',
+	'hw_graphic' => undef,
+	'hw_monitor' => undef,
+	'hw_mouse' => undef,
 	'late_dm' => 'no',
 	'netbios_workgroup' => 'slx-network',
-	'nis_domain' => '',
-	'nis_servers' => '',
-	'sane_scanner' => '',
+	'nis_domain' => undef,
+	'nis_servers' => undef,
+	'sane_scanner' => undef,
 	'scratch' => '/dev/hdd1',
-	'slxgrp' => '',
+	'slxgrp' => undef,
 	'start_alsasound' => 'yes',
 	'start_atd' => 'no',
 	'start_cron' => 'no',
@@ -579,12 +581,12 @@ my $shouldBeAttrs31 = {
 };
 foreach my $key (sort keys %$shouldBeAttrs31) {
 	is(
-		$fullMerge31->{attrs}->{$key} || '', $shouldBeAttrs31->{$key} || '', 
+		$fullMerge31->{attrs}->{$key}, $shouldBeAttrs31->{$key}, 
 		"checking merged attribute $key for client 3 / system 1"
 	);
 }
 
-my $fullMerge13 = { %$mergedClient1 };
+my $fullMerge13 = dclone($mergedClient1);
 ok(
 	mergeAttributes($fullMerge13, $mergedSystem3),
 	'merging system 3 into client 1'
@@ -629,12 +631,12 @@ my $shouldBeAttrs13 = {
 };
 foreach my $key (sort keys %$shouldBeAttrs13) {
 	is(
-		$fullMerge13->{attrs}->{$key} || '', $shouldBeAttrs13->{$key} || '', 
+		$fullMerge13->{attrs}->{$key}, $shouldBeAttrs13->{$key}, 
 		"checking merged attribute $key for client 1 / system 3"
 	);
 }
 
-my $fullMerge33 = { %$mergedClient3 };
+my $fullMerge33 = dclone($mergedClient3);
 ok(
 	mergeAttributes($fullMerge33, $mergedSystem3),
 	'merging system 3 into client 3'
@@ -679,7 +681,7 @@ my $shouldBeAttrs33 = {
 };
 foreach my $key (sort keys %$shouldBeAttrs33) {
 	is(
-		$fullMerge33->{attrs}->{$key} || '', $shouldBeAttrs33->{$key} || '', 
+		$fullMerge33->{attrs}->{$key}, $shouldBeAttrs33->{$key}, 
 		"checking merged attribute $key for client 3 / system 3"
 	);
 }