Expression Builder and using SQL in MS Access

[aroojee]

First hello to every one in this forum.

Well I am using MS Access 2003 for building a database.

I am usign 3 tables.

1. Students
2. Books
3. Request

Both student and books table has one to many relation with request table.

I am using MS Access Forum for all tables.

Now when I use Request table to issue a book to a student every thing goes
fine but the problem is that.

" When a book is issued to a student ,there is a field name "Avalibility" in
Books table which should show unavalible when book is issued. [By default
it is set to avalible]

Kindly tell me how to do this ?

Full view of relationship is as follows:

http://img2.freeimagehosting.net/image.php?d43d71cb6c.jpg