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Introduction to Data Dictionaries

In Visual DataFlex, an application’s business rules are defined in and managed by "Data Dictionaries". Data Dictionaries are a middle tier between your application’s user interface and your data that deliver the following advantages:

  • They let your application interact more effectively with your database – Data Dictionaries provide your application with a wealth of application-related information about your database that is not part of your physical database. It extends your database.

  • They protect your data – Data Dictionaries validate all database updates to make sure that only the right information is created, changed or deleted.

  • They centralize application logic and reduce application maintenance and programming errors. All of the information and rules about a Table and how it is managed is stored in one place - the Data Dictionary.  If you need to make an application logic change, you make it in the Data Dictionary and all parts of your application acquire the change.

Data Dictionaries are defined as Visual DataFlex classes. You create a Data Dictionary class for each table in your database. These classes will be used while you build your application and when you run your application.

Using Data Dictionaries while Building a Visual DataFlex Application

While you are building your application the Visual DataFlex Studio will automatically use the information in your Data Dictionary classes to assist you in the development process. This information is used when you build Windows entry views, Reports and web pages. The Studio and its wizards will use the Data Dictionaries to determine:

  • What tables should be opened and how they should be connected

  • What kinds of controls should be used for a particular field (e.g., form, checkbox)

  • What the labels and context help text should be used for your controls

  • When lookup lists should be used, how it should be used, and how it will look.

Properly defined Data Dictionaries make it easy to rapidly create good looking, consistent, reliable and maintainable applications.

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