DAG Tagging

Tags are a nice way of organizing a collection of objects. An item may have more than one tag, indicating membership in several different groups.

Hierarchical folders are also a nice way of organizing a collection. Hierarchy adds power: an item in a subfolder is automatically a member of all of its parent folders. However, folders may only have one parent.

DAG tagging combines the power of both techniques. Items are tagged, and the tags are themselves organized into a Directed Acyclic Graph.