Following each retrieval call, the status of the call whether successful or not needs to be checked. There is a two-position field in the PCB called status code field. It keeps track of what happened as a result of the call.
When GU call is used to retrieve segments to an existing database, the status codes for the following codes needs to be checked. " "(Blank), "GE".
Blank indicates that the retrieval call is successful. Return Status "GE" indicates that the segment could not be found.
When GN call is used to retrieve segments to an existing database, the status codes for the following codes needs to be checked. " "(Blank), "GE", "GA", "GK", "GB".
Blank indicates that the retrieval call is successful. Return Status “GE” indicates that the segment could not be found. In scanning though the database sequentially, a program normally test for the GB status code to find out when the end of the data base has been reached.
If the program issues another call after the GB status code has been returned, IMS goes back to the beginning of the database. When a program issues unqualified Get-Next calls, it can test for the GA and GK status codes to help determine which segment type has been retrieved. When a call retrieves a segment at a higher level, IMS returns a status code of GA. If the call retrieves a segment of a differrent type, but at the same level, IMS returns a status code of GK.
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