Overview of Navigational Database Access

Database Access Commands › Navigational DML › Overview of Navigational Database Access

Overview of Navigational Database Access

To use navigational DML commands effectively in a process, the application developer should be familiar with database programming concepts. These concepts are discussed in detail in the CA IDMS Navigational DML Programming Guide.

Considerations

The following special considerations apply to accessing the database in the CA ADS environment:

Before coding database commands, the application developer must be familiar with the characteristics of the subschema associated with the dialog. The subschema specifies the elements, records, sets, and areas available to the dialog. The subschema also includes the default usage modes for the database areas and specifies any restrictions on the use of database commands.
The default usage mode for a database area can be specified with the FORCE option. In some cases, using the FORCE option enables adding an area to a subschema without recompiling the ADS dialogs that use it. However, we recommend not to use FORCE with ADS applications that use extended run units. In such cases, a forced automatic READY might ready the area in the default usage mode on the 1^st dialog, but a lower-level dialog might need to READY the area in a more restrictive mode. This situation can lead to an unexpected failure of the ADS application.
Note: For more information on the limitations of using the FORCE option with ADS dialogs, see the Area Statement section (in the Subschema Statements chapter) in the CA IDMS Database Administration Guide.
Each database command can be coded any number of times within a process.
If a READY command specifies the same area more than once within a process, the usage mode specified in the last READY statement applies to the specified area for the entire process.
The READY command is executed when the first DML command is encountered. If an invalid (non-zero) error status is returned from the READY or BIND processing, the dialog aborts. Process code cannot intercept these errors.
At runtime, CA ADS automatically initializes a buffer for each record type associated with the mainline dialog. Subsequent dialogs that access the same record type use the existing record buffer unless a reinitialized buffer for the record is requested by using the Records and Tables screen during dialog compilation.
To enable proper positioning and movement through the database during the execution of an application, the CA ADS runtime system automatically maintains database keys for the records that are accessed by a dialog as shown in the following table.

Record	Description
Current of run unit	The most recently accessed record occurrence
Current of record type	The most recently accessed occurrence of each record type
Current of set type	The most recently accessed record occurrence (owner or member) of each set
Current of area	The most recently accessed record occurrence in each area

Database commands use and update currencies, as listed in the currency chart below.

CA ADS saves or releases the currencies established during dialog execution based on the command used to pass control to the next function or dialog.

Database command	Currency updated by successful execution				Successful execution

Database command	Run unit	Record	Set	Area	Successful execution
ACCEPT^*	X X X X				None
IF^*	X X				None
FIND/OBTAIN DB-KEY					All
FIND/OBTAIN CURRENT^*	X X X X				All
FIND/OBTAIN WITHIN SET	X				All
FIND/OBTAIN WITHIN AREA	X²				All
FIND/OBTAIN OWNER	X				All
FIND/OBTAIN CALC					All
FIND/OBTAIN DUPLICATE	X				All
FIND/OBTAIN USING SORT KEY	X				All
GET	X				None
STORE	X³				All
MODIFY	X				None⁴
ERASE	X				Nullifies of all record types and sets involved
CONNECT	X X				Run unit, set
DISCONNECT	X				Nullifies currency of object set; updates current of run unit and area
KEEP^*	X X X X				None
COMMIT					None
COMMIT ALL					Nullifies all currencies
ROLLBACK					Nullifies all currencies
ROLLBACK CONTINUE					Nullifies all currencies
FINISH					Nullifies all currencies

Note:

^*Uses only one currency as determined by command format.

²Required for NEXT and PRIOR formats only.

³All in which record type participates as an automatic member.

⁴ Except in the case of a sorted set.

More information:

Control Commands

Records and Tables Screen