Rational Programming Patterns for System z

-DC Lines in a Database Block

The -DC Lines tab is dedicated to the description of the CODASYL, DMSII, and TANDEM Database Blocks. You can declare the areas, call the records, and distribute them within the AREAS, call the SETS and describe them (name, label, parent, and child Segments).

This description is common to the following Block types:

-DC Lines definition

Network record type
Select a type of line among the authorized values:
Table 1. Type of line
Value Description
* Continuation of a set. For a set with multiple members, the first member Segment is indicated on an S-type line and the other Segments on *-type lines.
S Set (default option).
A Area,

TANDEM database

R Record.
Database object name
In this field, you enter the code which corresponds to the selected description line type.
  • Type 'S': Set code, on five characters
  • Type 'A': Area code, on five characters
  • Type 'R': Code of the area to which the record belongs.
Segment
This field cannot be used if the type of line is 'A' (Area). Select the parent Segment or record depending on the type of description line selected.
  • CODASYL database:
    • If the type is 'R', you select the record code.
    • If the type is 'S', you indicate the parent Segment code.
  • TANDEM database:

    You enter the Segment code which corresponds to the called record. When the Database Block is generated, this code is displayed after the 'RECORD' clause.

    To modify the contents of this field, click Change. Then in the list which displays in a dialog box, select a Segment. You can also create a Segment.

Child Segment
This field can be used with an S-type line only. Select the child Segment code (member) by clicking the Change button, as for the Segment code.
From Segment
This field is active only for an R-type line (Record). In this field, you must enter the name of the physical file (file name), which supports the data. When the Database Block is generated, this name is displayed after the FILE IS clause.
Method name
Schema:

This field can be used with an S-type line only.

Subschema:

Only used for IDMS ('D3', 'D4' types), DM4 ('M3' type) and DMS ('S3' type) subschemas.

On an R-type line, you can change the description of the selected record.

Number of Occurrences of sets
This field can be used with an S-type line only. You enter the average number of occurrences of the child Segment that are linked to an occurrence of the parent Segment. This number is used for the activity calculation.
Area name, Set name or comment
CODASYL database:

Depending on the value of the 'Type' of line selected, you enter:

  • The name of the Set (S-type line),
  • The name of the Area (A-type line),
  • A comment (R-type line).
For an IDMS (D4) or DMS (S3) subschema:

You can select a subschema at the Block description level. To do so, on R-type lines, enter SS=n (with 'n' being the subschema number according to the definition). For an IDS2 (I3) subschema, it is possible to call an object (area, record, set) without redescribing it, by specifying: INCLUSION.

TANDEM database:

You enter the name of the physical file which supports the data. When the Database Block is generated, this name is displayed after the 'FILE IS' clause.

-GG Lines

The -GG lines section is displayed when you enter or click a -DC description line. In this section, you can enter information to complete the description line.

In the -GG lines, you can modify the information contained in the Block Description lines before they are generated. Depending on the type of description line, lines are automatically displayed, in order to guide you when you enter the physical information of the Block. These lines are identified by 'VIRT' or 'GUID' in the last field of the table of the -GG lines. Collectively, these lines are called 'virtual' lines. The lines identified by 'VIRT' are generated. To modify these lines, you must override them and create new lines between beginning and end insertion lines. When you select a virtual line and click Override, the 'VIRT' or 'GUID' line is changed into a 'FromVIRT' or 'FromGUID' line. Then it can be modified. You can also edit the FromGUID and FromVIRT lines by selecting them and pressing the F2 key. You can create lines anywhere in the table. However if you want them to be taken into account at generation time, you must identify them with a G Type.

Type
  • To modify the description of -DC lines, you can use the following lines:
    • *: to generate comment lines,
    • G: to override the automatically generated elements,
    • V: to indicate data before the data set,
    • P: to type lines before the data set description ('population' for instance),
    • Z: to enter clauses located after the data set description (physical options for instance).
Description
This field must be used to enter the generation elements or comments you want to be generated. You can use the virtual lines to specify the physical characteristics of the areas and sets (DMCL), including the information related to sort keys and insertion modes.

For more details on the generation lines, see the explanations about generation lines in Creating -GG lines associated with this page.


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