HSQLDB - which is the main database file

I am using HSQLDB in the embedded mode.

jdbc:hsqldb:file:abc\\TESTDB;

After creating the database, the folder abc has the following files:

TESTDB.lck TESTDB.script TESTDB.log TESTDB.properties

My application is working properly

But my question is which is the main database file amongst the above-listed files?

Or is the main database file stored in some other location?