IDB files, are IDA Pro Database files. Its a proprietary format, but the information can be accessed via IDA Scripts ( IDC) or plug-ins. There are plug-ins that will dump the information to a SQLite DB.
Actually idb files are just archive files for the real data which is stored across four files *.id0, *.id1, *.nam and *.til file. Internally, the data is stored in a btree structure that you would need to reverse engineer yourself.