Analysis links

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Overview
Creating a link
Notes
Owner file and member file
Referential integrity

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Analysis links

Overview

The links are used to link the date files described in an analysis between themselves.

Several types of links are available. See Types of links for more details.

Reminder: The "LDM" and "Analysis" terms are indifferently used to define the structure of the database associated with a project.

Creating a link

To create a link:

On the "Analysis" pane, in the "Creation" group, click "New link". The mouse cursor turns into a pen.
Click the two data files that must be linked. The wizard for link description is automatically opened.
To define the cardinalities between the two files:
- select the cardinalities among the proposed ones (0, 1; 1, 1; 0, N; 1, N).
- answer the questions asked. The cardinalities will be automatically updated.
To define the advanced cardinalities, check "Display the advanced cardinalities" and answer the questions asked.
Type the link caption by briefly describing the link purpose. Go to the next step.
Specify the keys to link. Go to the next step.
Define the integrity rules. These rules are used to ensure the data integrity when one of the relation keys is modified or deleted.
Validate. The link is automatically created.

Remarks:

See Cardinalities for more details.
Versions 16 and later
If the data files to link contain an identical unique composite key (and also contain the items included in the composite key), a link can be performed on this composite key.
New in version 16
If the data files to link contain an identical unique composite key (and also contain the items included in the composite key), a link can be performed on this composite key.
If the data files to link contain an identical unique composite key (and also contain the items included in the composite key), a link can be performed on this composite key.

Notes

Owner file and member file

When there is a link between two data files, there is an owner file and a member file:

the owner file is the key owner.
the member file is a member of analysis files containing a copy of key.

To manage the link between two data files, the key of the owner file is copied to the member file.

For example, the key of the "Supplier" file is copied to each record of the "Product" file. Several records in the "Product" file can have the same key as the "Supplier" file:

the owner file is"Supplier",
the member file is "Product".

This type of link is represented as follows:

Referential integrity

The referential integrity of a database corresponds to the respect of constraints implied by the links between the data files.

The referential integrity consists in checking that:

if a record is deleted from the owner file, the corresponding records are also deleted from the member files,
if a record is added into a member file, a corresponding record exists in the owner file,
if a record is modified in the owner file, the unique key is not modified,
...

The check of referential integrity depends on the nature of the link between the data files.

Related Examples:

Training (WINDEV): WD Reflexive link

[ + ] This example presents the management of a reflexive link with the WLanguage functions.
The following topics are presented in this example:
1/ Fill a control with HFSQL content (automatic management of reflexive link).
2/ Fill by programming.