Motivation:
Currently, tags are organized as "single tag hierarchies". This makes the tagging of images with multiple tags rather tedious - especially if images are tagged ("later on")

Example:
An event may be described as a tuple (event_type, organizer, date, location, topic, participants), whereby each component may be elements in different branches of the tag hierarchy.
If, later on, additional images are imported which belong to the same event, all single components have to be tagged again

Proposal:
The concept of "named tag groups" is introduced as follows:
1. the user can define a named tag group "CeBIT 2013" as (fair, Hannover, 2013, IT). If later on, new images are imported, they can easily be tagged with "CeBIT 2013".
2. new "fair-events" can be generated by generation a copy of "CeBIT 2013", and then modifying the components with sibling tags.

GUI:
1. right pane / tag section: the tag group can be generated by identifying the corrensponding component tags (as is) and storing the group under a group name (new)
2. right pane / filter section: tag groups can be selected/deselected, "must have", "must not have" in the same way as single tags
3. left pane / my Tags: to by extended by "tag groups"
4. left pane / search: search groups to be extended by "tag groups" (Remark: tag groups can already be defined by set of search groups with single tags each)