Do Library Automation Vendors use a Standard DBMS like ORACLE?

I have a question regarding what commercial DBMSs are used by the major library automation vendors. Some of my questions are: a) Who are the major vendors for library automation ? b) Do those vendors build their library schemas on top of some commercial DBMS like DB2, RDB, ORACLE, SYBASE, INFORMIX, INGRES or do they use their own DBMS (relational I presume)? c) What are the advantages and disadvantages of not using a standard DBMS for a particular application? Are there some database applications where they do not use a standard DBMS? I heard NCR supplies a database application for Grocery Stores which does not use a standard DBMS. Thanks a lot. Prasad Polamraju rvp2f@virginia.edu