Hypatia depends heavily on the Zope Object Database (ZODB). Because ZODB is less a database and more a persistent object store (it doesn't possess a query language; Python is its query language), it has been necessary to create indexing and searching facilities for data stored in ZODB.
The first iteration of searching and indexing for ZODB-based applications (at least post-Principia, which had something named Tabula, which I never actually used) was the ZCatalog. The ZCatalog was entirely tied to Zope2, and still remains in heavy use today within Zope 2 applications such as Plone.
The second iteration was
zope.app.catalog, which was a ZCatalog do-over
for Zope 3 applications.
Neither of these searching and indexing packages are particularly easy to use
outside of a Zope application. Each makes various assumptions about the
content objects that need indexing or the environment that aren't appropriate
for arbitrary applications. For instance, ZCatalog wants objects you want to
catalog to have a
getPhysicalPath method which returns a "path". An
zope.app.catalog makes the assumption that that it's located
within a Zope 3 "site" object within a ZODB, and assumes that you want query
result sets to be sets of Python references to the original object you
indexed. In other words, these packages assume too much to be maximally
useful outside the context in which they were developed. Repoze is a project which has as a stated goal making it
easier for non-Zope Python developers to use Zope technologies outside Zope,
so this seemed like a natural thing to do under the Repoze flag.
Hypatia is a reboot of both zope.index and repoze.catalog with no backwards compatibility constraints.