What is IMS DB PCB Mask?

PCB stands for Program Communication Block. PCB Mask is the second parameter used in the DL/I call. It is stated in the linkage section. Given below is the syntax of a PCB Mask:

here are the key points to be aware:

  • For each database, the DL/I continues a place of storage that is known as the program communication block. It stores the data approximately the database which might be accessed by the utility programs.
  • The entry statement creates a connection among the PCB mask in the Linkage section and the PCBs within the program’s PSB. The PCB masks used in a DL/I call tells which database to use for operation.
  • you can assume this is similar to specifying a file name in a COBOL read statement or a recorded call in a COBOL write assertion. No select, ASSIGN, OPEN, or close statements are required.
  • After each DL/I name, the DL/I shops a status code within the PCB and this system can use that code to determine whether the decision succeeded or failed.

PCB Name

Points to note:

  • PCB Name is the name of the area which refers to the entire structure of the PCB fields.
  • PCB Name is used in program statements.
  • PCB Name is not a field in the PCB.

DBD Name

Points to note:

  • DBD name contains the character data. It is eight bytes long.
  • The first field in the PCB is the name of the database being processed and it provides the DBD name from the library of database descriptions associated with a particular database.

Segment Level

Points to note:

  • Segment level is known as Segment Hierarchy Level Indicator. It contains character data and is two bytes long.
  • A segment level field stores the level of the segment that was processed. When a segment is retrieved successfully, the level number of the retrieved segment is stored here.
  • A segment level field never has a value greater than 15 because that is the maximum number of levels permitted in a DL/I database.

Status Code

Points to note:

  • Status code field contains two bytes of character data.
  • Status code contains the DL/I status code.
  • Spaces are moved to the status code field when DL/I completes the processing of calls successfully.
  • Non-space values indicate that the call was not successful.
  • Status code GB indicates end-of-file and status code GE indicates that the requested segment is not found.

Proc Options

Points to note:

  • Proc options are known as processing options which contain four-character data fields.
  • A Processing Option field indicates what kind of processing the program is authorized to do on the database.

Reserved DL/I

Points to note:

  • Reserved DL/I is known as the reserved area of the IMS. It stores four bytes binary data.
  • IMS uses this area for its own internal linkage related to an application program.

Segment Name

Points to note:

  • SEG Name is known as segment name feedback area. It contains 8 bytes of character data.
  • The name of the segment is stored in this field after each DL/I call.

Length FB Key

Points to note:

  • Length FB key is known as the length of the key feedback area. It stores four bytes of binary data.
  • This field is used to report the length of the concatenated key of the lowest level segment processed during the previous call.
  • It is used with the key feedback area.

Number of Sensitivity Segments

Points to note:

  • Number of sensitivity segments store four bytes binary data.
  • It defines to which level an application program is sensitive. It represents a count of number of segments in the logical data structure.

Key Feedback Area

Points to note:

  • Key feedback area varies in length from one PCB to another.
  • It contains the longest possible concatenated key that can be used with the program’s view of the database.
  • After a database operation, DL/I returns the concatenated key of the lowest level segment processed in this field, and it returns the length of the key in the key length feedback area.

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