What is the language definition language?

Data definition is a language for programming a computer or scripting that defines the data structure. By definition, these languages ​​must do three things - to create, remove and edit data structures. What they do outside these three areas is irrelevant if they perform these three tasks. Any language may be a language definition language, but the term is most often used on the structured language schemes (SQL) and the expandable brand language (XML) language. The process defined two main areas of data structure - the language definition language has made the actual database structure and the manipulation language has defined the data placement methods in the structure. Since then, these two terms have expanded and have become general conditions for the processes they cover.

General terms now apply to any language that performs their original functions. Both SQL and XML perform all the required tasks and provide many features that have been missing in the original model because they have not yet been invented. These capabilitiesother languages ​​are also guessed; They are used much less often.

In order to make the language definition, the language must provide three functions. The first main function is the design of data structures; In principle, these are tables designed to hold specific groups of information. They often look like a table and stick to the pages of cross -referenced information. For example, a list of customers can have a company list on the one hand and a list of available products along the top. The list should have a list where these customers bought individual products on the table parts.

Another main feature is to delete the date. This is not the same as erase the entire database or file; It's a much more selective process. It can remove a specific page of information or the entire part of a multidimensional field. In both cases, the data must be removed without affecting other data structures, although all are held in the same file.

LastThe main function is to change the data structure. This is a wide category that covers many situations. The table may have added or renamed columns, or it may be necessary to divide the entire database into two different databases. In any situation, it must be changed so that no information is lost, destroyed or created during the process. This prevents anomalous information from entering the data system.