Project IDs may be related to other project IDs by Links (Hierarchical or PeerProject) or by Groups. Project IDs may be related to other project IDs by Links (Hierarchical or PeerProject) or by Groups. An adhoc list of project IDs that are logically related in some manner. Groups provide a means to support retrieval and display for corner cases that are not otherwise supported by direct links (hierarchical or peer) or by available database indexing/query retrieval support. Any archive database may assert a group without any ownership restriction (of the project). Archives may opt to validate asserted groups and may opt to either accept for display or not. Groups can include submitter-level projects (any project type) and/or administrative projects Reference to project where links originate. Links direction is always from lower level project to the higher level project. This element is a lower level part. Example: child in a hierarchical relationship; parasite in a parasite-host relationship. Vertical Hierarchical relationship, project points to the administrative top members (Top Single or Top Miltiple, depending on "type" attribute). In a directional link between lower level and higher level projects this element is a higher level part. Member projects of a group - list archive ids It is possible to name this relationship when needed Pairwise peer-to-peer relationship for the project; Hierarchical restrictions do not apply. In a directional link between lower level and higher level projects this element is a higher level part. Example: host in a parasite-host relationship. ID (archive name as an attribute and unique across this archive accession as an element value) created by archive. Identifies group itself but not projects included in the group. TGR- Perhaps explain how this is different than ProjectIDRef. Reference to project that included in the group ID created by archive Group type is a controlled vocabulary. Corresponds to GroupTyypes.abbr in the DB. Short text that displayd in the presentation. TGR - add descriptive text - how is it different than Description.