PHP and database schemas

I was wondering if anyone had any experience with cross-database layers (e.g. MDB2) which had support for schemas. By "Schemas" I don't mean "the structure of a table", but rather the term as used in PostgreSQL, where within one database you can have alice.messages and bob.messages as two seperate tables both individually named "messages" but in "alice" and "bob" schemas.

I'm trying to see if there's a good abstraction layer I can use which somewhat provides this kind of namespace functionality, at least for Postgresql. (AFAIK MySQL doesn't have that kind of schema, not sure about SQLite.)

http://dev.mysql.com/doc/refman/5.1/...n-options.html