e4Graph is a C++ library that allows programs to store graph-like data
persistently and to access and manipulate that data efficiently. With
e4Graph, you can arrange your data in the most natural form that reflects
the relationships between its parts, rather than having to force it into
a table-like format. The e4Graph library allows you to concentrate on the
relationships you want to represent, and not on how to store them in a
database. You can modify data items, and add and remove connections and
relationships between pieces of data on the fly. e4Graph allows you to
represent an unlimited number of different connections between pieces of
data, and your program can selectively manipulate the data according to
the relationships it cares about, not having to know about other connections
represented in the data set.

WWW: http://e4graph.sourceforge.net/