Rational Programming Patterns for System z

The Logical View entity

A Logical View defines an information concept in your company data system. It is constituted of a collection of elementary data, which are Data Elements. It is conveyed between the server and the client parts through the message that both parts exchange to communicate. To be used in an eBusiness application, a Logical View must be called in a Business Component. This Component makes the link between the structure of the storage entities (Segments) and the structure of the Logical View. As it is described at a logical level, the same Logical View can be used by more than one Application.

Logical View definition

Since a Table or View is like a Segment, it is defined from a Segment entity. You specify that the Segment is a Logical View in the Segment creation wizard, by selecting the Logical View value in the Segment type field. As a result, a Logical View is created and saved in the Design Explorer under the Segment entity repository. When you double-click a Logical View instance or right-click and select Open, the Logical View editor opens. Then you can click the Definition tab to define the Logical View instance.

Note: It is advised to define a Business Component for each Logical View, in order to facilitate the reuse and hence the maintenance of Logical Views.

Description

The Logical View description is composed of the list of its columns. The external resources (constant data) are described in Data Elements, Data Structures, and Segments and are called in -CE Lines tab. You will also describe Database Blocks if constant data is stored in a database. With the DBD Complement tab in the Segment editor, you specify the source (tables) of the elements (columns) called into Segments used as Views.

In each section defining an element call in the -CE Lines tab, you must indicate:
  • The identifiers,
  • The extraction method parameters,
  • The data transfer.

Among the data which describes an information occurrence, you must determine which are the identifiers. These identifiers are Data Elements which will be used as selection criteria or start key for the reading of data occurrences in the database. In the list of Data Elements of the Logical View, you specify identifiers by assigning them the U type (TYPE column).

When a client calls a selection service, this service may implement an extraction method and its parameters by value. The Business Component which answers the call must recognize the extraction method and its parameters to correctly perform the service. The only way to send this information is through the message sent by the client. The extraction method is sent to the Business Component through the technical part of the message. Parameters must be described in the application part of the message, that is in the Logical View. In the -CE Lines tab, you specify the parameters by value for all the extraction methods which may be used by the Logical View. To do so, you must call Data Elements defined in the repository.

To implement a selection service, data must be transferred from the Segments to the Logical View, after the accesses to external resources have been specified. To implement a check and update service, data must be transferred from the Logical View to the Segments, after specifying the accesses to external resources for checking and before specifying the accesses for updating. These data transfers are automatically generated by mapping the Data Elements of the Logical View with the Data Elements of the Segments. You specify this mapping in the -CE Lines tab of the Logical View.

Subschemas

You can select the Data Elements called in the view, by:
  • Checking a subschema number ranging from 0 to 9 in a wizard that opens in the Data Element call, Segment call, or group definition section of the -CE Lines tab in the Logical View editor. As a consequence, a 'O' number is automatically displayed in the Subschema column of the Data Element, Segment or group call line in the -CE lines tab for each subschema checked. The position in the column of the 'O' corresponds to the subschema number checked (O represents 10).
  • Or selecting 'ALL' in the -DR Lines tab of the Database Block editor, in the Key type field. This value means that all the Data Elements of the Segment belong to the View.
  • In cases of a selection by a number ranging from 0 to 9, on the -SS Lines tab of a Logical View editor, an 'S' (indication of a subschema) is automatically indicated on the line when you enter a subschema line.

Then, to define subschemas, you must create Subschema lines in the -SS Lines tab of a Logical View editor. A 'S' letter (indication of a subschema) is automatically indicated on the line when you enter a subschema line. You must enter a number and name for each subschema created.


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