To the first question, I don't know which properties are verifiably impossible to have in an OODB, but would be quite interested. I think one would first need a

To the first question, I don't know which properties are verifiably impossible to have in an OODB, but would be quite interested. I think one would first need a more thorough definition of what actually constitutes an OODB (and OO, for that matter.). To the latter: Yes, of course. Tutorial D and all that. Personally, I'm not doing anything at the moment for which Twitter-esque scalability is really a requirement (though hardly anyone is, honestly). Postgresql is a sufficient large RDBMS, for my purposes, SQLite works nicely as a smaller one, and below that, in-memory Lua tables, Python dicts, or Scheme sexps are fine. I'm mostly curious about what alternative database-like tools could be made for roughly the same domain as SQLite. To some extent, that could overlap with objects, but OOP is not in any way a requirement for me. (There may be some intersection with filesystems, too; they're databases, after all.)