Defining Segments, Files, and Areas › Procedure for Defining Segments

Procedure for Defining Segments

Steps

Note: When copying an SQL segment definition to the application dictionary, you do not need to define the files.

Example of a Non-SQL Segment Definition

The following example creates a segment for a non-SQL defined database. The statements in the example define the segment and its associated files and areas. The characteristics of the segment are:

• Segment EMPSEG—By default, CA IDMS/DB assigns these values:
  • Page group: 0
  • Maximum records per page: 255
• File EMPDEMO1—EMPDEMO1 is a non-VSAM file with a dataset name of CORP.SYSPUB.EMPFILE1. It will be accessed using a ddname of EMPFILE1 unless overridden by a DMCL parameter
• Area EMPAREA—Area EMPAREA has the following attributes:
  • 2000 pages, starting on page 990001 and ending on page 992000. These pages will be used to store record occurrences assigned to the area. The definition does not provide for future expansion of the area because it does not specify a MAXIMUM SPACE clause.
  • Pages size of 6000 bytes.
  • A symbolic subarea, CALC-RANGE, which starts at page 990002 and extends for the remainder of the area.
  • A symbolic index, EMP-LNAME-NDX, which is a sorted index based on an index key of 10 characters and estimated entry count of 10,000
  • An association with file EMPDEMO1 that, by default, contains the entire area, beginning on block 1 of the file.

    create segment empseg;
    
    create file empseg.empdemo1
       assign to empfile1
       dsname 'corp.syspub.empfile1'
       disp shr;
    
    add area empseg.emparea
       primary space 2000 pages
           from page 990001
       page size 6000 characters
       subarea calc-range offset 1 for 100 percent
       symbolic index emp-lname-ndx
           based on sorted key length 10 for 10000 records
       within file empdemo1;
    

Example of an SQL Segment Definition

The following example defines a segment and its associated areas and files for an SQL-defined database. The characteristics of the segment are:

• Segment PRODSEG—This segment has the following characteristics:
  • Is associated with SQL-schema PRODSCHM; that is, the areas in segment PRODSEG are reserved for tables in schema PRODSCHM
  • Maintains synchronization stamps at the area level (rather than the table level)
  • By default, belongs to page group 0 and contains up to a maximum of 255 rows per database page

  You must define the segment in both the application dictionary that will contain the schema and table definitions and in the system dictionary.

• Files EMP_DEMO1 and PROJ_DEMO1—Both files are VSAM database files. At runtime, CA IDMS/DB looks in the JCL for a file specification with a matching ddname.
• Areas EMP_AREA and PROJ_AREA—The definitions of both areas allow for future expansion by using the MAXIMUM SPACE clause.

  For example, area EMP_AREA contains 1500 pages beginning on page 80001 and ending on page 81500. The first 1000 pages are the initial allocation. The remaining 500 pages are reserved for future expansion of the area. Additionally, the synchronization stamp for area EMP_AREA is by table, overriding the specification made at the segment level.

  create segment prodseg
     for sql
     for schema prodschm
     stamp by area;
  
  create file emp_demo1
     assign to empfile
     vsam;
  
  create file proj_demo1
     assign to projfile
     vsam;
  
  create area emp_area
     primary space 1000 pages
         from page 80001
     maximum space 1500 pages
     page size 6000 characters
     stamp by table
     within file emp_demo1;
  
  create area proj_area
     primary space 1000 pages
         from page 82001
     maximum space 1500 pages
     page size 6000 characters
     within file proj_demo1;