IMS

This document covers the following topics:

IMS Segment Layouts and Userviews - File Types J and K

Attributes

The following attributes of an IMS segment (type I) are shown for that file and for the related files of types J and K.

Note:
Parameters not listed below are described in other sections of this documentation: Parameters common to all object types, for example Keys, are described under Global Attributes. Parameters common to all file types, for example Literal name, are described under Common File Attributes. See also Common Parameters for SQL File Types.

Parameters
Segment name The name of the IMS segment from which the related Predict file object of type I was incorporated.
min. length The minimum length of the IMS segment (zero if the length is fixed).
max. length The maximum length of the IMS segment (if it is fixed).
Segment type

The type of the IMS segment. Possible values:

Logical child (C)
Logical (L)
Physical (P)
Virtual (logical) child (V).

Segments of type logical occur only in logical IMS databases. Segments of types child, physical and virtual occur only in physical IMS databases.

Parent The ID of the Predict file object of type I incorporated from the parent segment of the IMS segment (the segment one level above it in the hierarchical structure of the IMS database). For a root segment, this field is left blank.
Source-1 The following rules apply:

  • For a segment of type V, the ID of the Predict file object of type I that was incorporated from the related segment of type C.

  • For a segment of type L, the ID of the Predict file object of type I that was incorporated from the segment of a physical database from which this segment of a logical database is derived.

  • For a segment of type CHILD or P, this field is left blank.

Source-2 The following rules apply:

  • For a segment of type LOGICAL derived from a segment of type C, the ID of the Predict file object of type I that was incorporated from the logical parent of the segment of type C.

  • For a segment of type LOGICAL derived from a segment of type V, the ID of the Predict file object of type I that was incorporated from the logical parent of the segment of type V (the physical parent of the related segment of type C).

  • For any other segment, this field is left blank.

Editing Field Lists of IMS Files

Restrictions that apply when editing a field list of an IMS file depend on the type of the IMS file and are described in the table below.

File Type Restrictions
I (IMS Segment)

The following attributes can be maintained: ID, keywords, owners, abstract, format, NAT hdr1-3 (Natural headers), NAT editm (Natural edit mask), 3GL specification, Condition name & value and Field name synonyms. See Defining Basic Attributes of Fields and Defining Additional Attributes of fields in the section Field in this documentation.

No fields can be added or deleted. Format changes are rippled across related files of type J or K. Only the following changes of format are allowed:

  • between P (packed) and PS (packed signed);

  • between P6 or P7 and D (date);

  • between P12 or P13 and T (time).
J (IMS Segment Layout) The following rules apply:

  • A file of type J can contain user-defined fields and fields of the related file of type I. The two-character short names of the user-defined fields must fall within the range preceding the parameter Start in logical defined by the DDA in the Miscellaneous defaults of the Modify General Defaults function. Its value is normally HA.

  • Fields of the related file of type I that are included in a File of type J must have the same attributes in the File of type J as they have in the file of type I.

  • Their offset in the file of type J must be the same as their IMS-OFFSET in the file of type I.

For a variable-length segment, only one field in one file of type J can be defined as variable length.

  • If it is a field, it must be the last field in the segment.

  • If it is a multiple value field or a periodic group, it can be anywhere in the segment.

  • However, if it is not the last field, its maximum occurrence must be specified.

Predict checks that the above conditions are met when the field list of the file is cataloged. Changes to user-defined fields are rippled across related files of type J or K.
K (IMS Userview) A file of type K can contain fields of the related file of type I and fields of all related files of type J. ID, keywords, owners, comments, format, NAT hdr1-3 (Natural headers) and NAT editm (Natural edit mask), 3GL specification, Condition name & value and Field name synonyms can be maintained.