Introduction to CA IDMS Data Manipulation Language › Programming in the CA IDMS Environment › Navigational DML

Navigational DML

Navigational DML statements allow you to access database records and sets one record at a time, and to check and maintain currency in order to assure correct results. Navigational DML statements give you control over error checking and flexibility in choosing database access strategy. To use this type of DML statement, you must have a thorough knowledge of the database structure. For an Example of a data structure diagram, see Sample Programs and Database Definition.

Navigational DML statements provide:

• Control over error checking ─ You can check on the results of processing each statement.
• Flexibility in choosing database access strategy ─ You can enter the database either sequentially (area sweep) by using a symbolic-key value (CALC or index), or by using a database-key value (DIRECT).

There are four types of navigational DML statements:

• Control statements initiate and terminate processing, effect recovery, prevent concurrent updates, and evaluate set conditions.
• Retrieval statements locate data in the database and make it available to the application program.
• Modification statements update the database.
• Accept statements pass database keys, storage address information, and statistics to the program.

Example of Navigational DML Statements

The following figure illustrates a database structure containing two owner records (EMPLOYEE and JOB) that share one member record (EMPOSITION), and lists the statements used to find employee and job information. To obtain EMPLOYEE and JOB information, you would retrieve an EMPLOYEE record, the first EMPOSITION record in the EMP_EMPOSITION set, and the owner record in the JOB_EMPOSITION set.