Essay: Defining Data – Making data understandable

Sample Essay

By defining data, we mean, assignment of a field name, type of data to be storage and, field length and the storage method to be used for storing the data. In iSeries, the data can be defined externally and internally.  The internally defined data is defined within the application using the data definition commands of the programming language. Externally defined files are defined outside the applications using DDL (Data Definition Language).

Externally defined data offers an advantage over internally defined data such that the data is defined only once. On the iSeries, files can be defined internally using RPG, COBOL or any other supported languages, and externally using SQL, IDDU ( interactive data definition utility) or DDS ( Data Definition Specifications). Though the SQL offers a definition of data using interactive SQL utility or SQL programs, it also allows loading, viewing and modifying data from within the application programs. IDDU provides the capability to define data through a series of menus and screens. After the information is gathered, it generates and compiles DDS source to create the file.

DDS also allows for data definition which is stored in a source physical file member. It requires the user to create a library, source physical file and member to hold the DDS source code definition which is then compiled to create data physical file and member. When specifying a function or keyword for file, record or field, the scope that is affected by the keyword or function must also be defined. A physical file can only have one record level specification and at least one field level specification. A common practice that is used in most information systems is to store all fields’ definition in a single source physical file which is called field reference file and data in other files.

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