Well, I came to the conclusion of my queries as follows.
(7) Advisory locking is what we know in databse terminology as
Optimistic Locking.
(8) Yes. And just to add, mandatory read locking is what we know in databse terminology as
Pesimistic Locking.
(9) Magic cookie is a value (in my case 4 byte numeric) that identies a data file as valid. In our project we only need to ensure that we have numeric 4 bytes at the start of our db.db file through our data conversion tool or what I say
File Parser, no more checking is needed. And magic cookie is no how related to our security code.
(10) key is something through which we can search a record for exact match to provide what I say
Strict Search Mechanism. My key is subcontractor name. Criteria is to provide what I say
Flexible Search Mechanism for partial or exact matching of any field.
(11) We are not needed to add or modify the db.db file's data from our program anyhow. We just need to read data for search and lock mechanism. Methods like createRecord() or updateRecord() in file parser will be
NOP methods provided only for future enhancement.
Please correct me if I am wrong.

[ October 10, 2002: Message edited by: Ashik uzzaman ]