<<Then, is there a blob filter which compresses (converts to ZIP format on teh
way in and then unzips on teh way out? Does filtering work on the way out as
well? i.e. unfiltering?>>

Depends on what you mean by exists, I have an old version that did this on Solaris and
InterBase 3.3 lying around somewhere, so I know its possible. I also know a few
companies that have written the same.....

The concept of a filter is that it performs "its operation" on storage and then
reverses the "operation" on display. Look at how BLR is stored in triggers for
example, this is a a filter..... displaying of textual blobs is also a filter...
By this I mean that Firebird has a few built in filters that understand how to
convert stuff on the way in and out. This could be extended......

Regards
Paul