GET

Key Characteristics

• • DL/I Interface: GET calls are part of the Data Language/I API, which is the standard interface for application programs to interact with IMS databases.
  • Segment-Level Retrieval: Data is retrieved at the segment level, meaning an entire segment occurrence is returned to the application program's I/O area.
  • Hierarchical Navigation: GET calls implicitly or explicitly navigate the hierarchical structure of an IMS database, moving down and across segments based on the call type and specified Segment Search Arguments (SSAs).
  • Program Communication Block (PCB): Each GET call operates using a PCB, which represents the application program's view of a database (defined by a PSB) and maintains its current position within that database.
  • Types of GET Calls: Includes GU (Get Unique) for direct access, GN (Get Next) for sequential processing, and GNP (Get Next within Parent) for sequential processing within a specific parent segment.
  • Segment Search Arguments (SSAs): Optional clauses used with GET calls to qualify which segment occurrences are to be retrieved, based on key fields or other criteria, enabling precise data selection.

Use Cases

• • Retrieving a Specific Record: Using a GU call with fully qualified SSAs to directly access a unique root segment and its dependent segments (e.g., retrieving a specific customer's entire profile).
  • Sequential Processing: Iterating through all occurrences of a specific segment type or processing segments within a particular hierarchical path using GN or GNP calls (e.g., listing all orders for a given customer).
  • Batch Reporting: Extracting large volumes of data from an IMS database for generating reports, performing analytics, or populating data warehouses.
  • Online Transaction Processing (OLTP): CICS transactions utilizing GET calls to quickly retrieve and display specific pieces of information (e.g., checking product availability or a customer's account balance).
  • Data Validation and Existence Checks: Reading existing data to verify its integrity, check for duplicates, or confirm the presence of related records before performing updates or insertions.

Related Concepts