There is typically one site-wide index space all other spaces delegate to. Typically it makes no sense to have Resource Types, Topic Types, or Experience Levels defined more than once. Often organizations define Subjects, Categories, and Tags also in one place to provide a common organization of pages that can be accessed by browsing. The homepages for those organizing document types are found in index spaces.

There may be a hierarchy of index spaces. For instance a site-wied index space for all basics and an index space for each major project or client.