Navigational DML Programming Techniques

This chapter discusses programming techniques used to access the database in navigational DML programs. Functionally similar DML statements are presented together; sample code that demonstrates typical usage of each statement is included. The navigational DML functions are divided into these categories:

Retrieving Records-Retrieving information from the database by using navigational DML statements
Saving DB-Key and Address Information-Saving db-keys and bind addresses
Checking For Set Membership-The two forms of the DML IF statement, used to obtain set membership information without performing any I/O
Updating the Database-Modifying, storing, erasing, connecting, and disconnecting database records
Accessing Bill-of-Materials Structures-Storing and retrieving records related as in a bill-of-materials structure
Locking Records-Restricting access to database records

This chapter also contains information on the following topics of relevance to the navigational DML programmer:

How page information can be used to make db-keys unique within the scope of a run unit
Currency and how it is used and updated by various DML statements
How to collect run-time statistics

This section contains the following topics:

DB-Keys and Page Information

Run Unit Currencies

Retrieving Records

Saving db-key, Page Information, and Bind Addresses

Checking for Set Membership

Updating the Database

Accessing Bill-of-Materials Structures

Locking Records

Implicit Record Locks

Collecting Database Statistics