Rational Programming Patterns

The derived instances

With this principle, you can create a derived instance from a reference instance and then use this derived instance to generate the reference instance without duplicating its design. There are two derivation types: the Design derivation and the Code derivation. With the Design derivation type, you create a derived instance to generate the instance from a Library different from the one specified in the reference instance. With the Code derivation type, you create a derived instance that inherits the complete source code (code generated from the design and specific code) of the reference instance.

Design derivation

This derivation type is available for the following entities: Program, Screen, Server, Data Structure (for the generation of the Copybooks and the error messages), Dialog (for the generation of the error messages), and Server Dialog.

It is useful when an instance must be generated from different Libraries (for example: A Program that must be generated for the CICS and IMS platforms). You can create a derived instance that points to a reference instance and to a generation Library. This derived instance does not contain any design. You can then generate the reference instance from another Library without duplicating its design.

To create the derived instance, you must use the creation wizard of the entity. For example, you use the Program creation wizard to create an instance that is derived from a Program instance. Enter its required fields and check the Derive box. Then, select Design derivation in the Derivation type field and specify the instance it is derived from in the <Entity> to derive field.
Tip: If you leave the Name empty, check the Derive box and enter the reference instance. The name of the derived instance is automatically initialized with the name of the reference instance. You just need to complement this name with the Library or any other distinctive code. This way, they can be easily associated among all the available instances.
The derived instance is displayed under the same entity as the instance it is derived from, in the same location of the Design Explorer view. Double-click the instance to open it. The derived instance contains the following tabs:
  • The Overview tab with a link to the reference instance that contains the design, and a link to the generation Library
  • The Definition tab for Program, Dialog, and Screen entities only. This tab displays the COBOL target and the generation variants elements
  • The -CR Lines tab that contains the links between entities, called 'references'
  • The Keywords tab
Then, you must generate the derived instance. It actually generates the reference instance but with the parameters of the generation Library that is selected in the derived instance.
Note: If the design of the reference instance has been modified, the generation of the derived instance takes this modification into account, except if the change was only a change of Library.

The generated COBOL file will be created, nested under this derived instance. This way, you can keep as many COBOL files of the same instance as there as generation targets.

Code derivation

This derivation type is reserved for entities in which specific code can be inserted: Programs, Screens, and Servers. It is useful when this specific code is distributed among various Libraries.

You can create a derived instance that does not contain any design but points to a reference instance. The derived instance inherits the complete source code of the reference instance.

When you generate a derived instance that was created with a Code derivation type, the following steps take place:
  • The instance that is referenced by the derived instance is generated if it has not already been generated, or if an element of its design has been modified.
  • The complete source code (the code generated from the design and the specific code) is passed on to the derived instance, where it is considered as the generated code. A reconciliation then synchronizes this generated code with the specific code of the derived instance.
Note: If you generate a derived instance, its reference instance is generated again if necessary, but the reverse is not true: If you generate a reference instance, its derived instance is not generated.

From the same design of the same Pacbase instance, you can then generate two source files with different COBOL codes. You can repeat these operations from the derived instance, by selecting it as the reference instance of a new derived instance.

The derived instance is simple because it contains one field only: a reference to the generatable instance (a Program, Screen, or Server).

To create the derived instance, you must use the creation wizard of the entity. For example, you use the Program creation wizard to create an instance derived from a Program instance. Enter its required fields and check the Derive box. Then, select Code derivation in the Derivation type field. You must specify the instance it is derived from (such as a Program, Screen, or Server, or the derived instance of these entities).
Tip: If you leave the Name blank, check the Derive box and enter the reference instance. The name of the derived instance is automatically initialized with the name of the reference instance. You just need to complement this name with any distinctive code. This way, they can be easily associated among all the available instances.
The derived instance is displayed under the same entity as the instance it is derived from, in the same location of the Design Explorer view. Double-click the instance to open it. The derived instance contains the following tabs:
  • The Overview tab with a link to the reference instance that contains the design, and a link to the generation Library
  • The Definition tab for Program and Screen entities only. This tab displays the COBOL target elements
  • The -CR Lines tab that contains the links between entities, called 'references'
  • The Keywords tab

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