[Zope-dev] difference between OOSet and OOTreeSet?

Hi All, Wondering if someone could tell me the difference between an OOSet and an OOTreeSet? They seem to have different interfaces and yet seem to be used in similar circumstances in PluginIndexes/common/UnIndex.py... I'm looking for a set-like data structure which will likely get pretty large over time and so I don't want the whole data structure written to disk each time I add a new item to the set. What should I be using? cheers, Chris -- Simplistix - Content Management, Zope & Python Consulting - http://www.simplistix.co.uk