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 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 Logical View in the Segment type field. As a result, a Logical View is created and saved in the Design Explorer under the Segment entity.

Note: It is advised to define a Business Component for each Logical View, to facilitate the reuse and 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 the -CE Lines tab. You 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 that are used as views.

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

Identifiers are Data Elements that will be used as selection criteria or start key for the reading of data occurrences in the database. You specify identifiers by assigning the Data Elements a U type.

When a client calls a selection service, this service can implement an extraction method and its parameters by value. The Business Component that 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 that can be used by the Logical View. To do so, you must call defined Data Elements.

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 in two ways:
  • Select 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 is automatically displayed in the Subschema column of the Data Element, Segment or group call line in the -CE Lines tab for each selected subschema. The position in the column of the O corresponds to the selected subschema number (O represents 10).
  • Select 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.

To define subschemas, you must create subschema lines in the -SS Lines tab of a Logical View editor. An S 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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