Describing database files

 

You can use several methods to describe i5/OS^® database files. This topic discusses how to describe a database file with data description specifications (DDS) because DDS has the most options for defining data.

If you want to describe a file just to the record level, you can use the record length (RCDLEN) parameter on the Create Physical File (CRTPF) and Create Source Physical File (CRTSRCPF) commands. If you want to describe your file to the field level, several methods can be used to describe data to the database system: interactive data definition utility (IDDU), Structured Query Language (SQL) commands, or data description specifications (DDS).

Interactive data definition utility (IDDU)

Physical files can be described with IDDU. You might use IDDU because it is a menu-driven, interactive method of describing data. You might be familiar with describing data using IDDU in a System/36™ environment. In addition, IDDU allows you to describe multiple-format physical files for use with Query, iSeries™ Access, and the data file utility (DFU).

When you use IDDU to describe your files, the file definition becomes part of the i5/OS data dictionary.

DB2 Universal Database™ for iSeries Structured Query Language (SQL)

SQL can be used to describe a database file. It supports statements to describe the fields in the database file and to create the file.

SQL was created by IBM to meet the need for a standard and common database language. It is currently used on all IBM^® DB2 platforms and on many other database implementations from many different manufacturers.

When you create a database file using the DB2 UDB for iSeries SQL, the file description is automatically added to a data dictionary in the SQL collection. The data dictionary (or catalog) is then automatically maintained by the system.

SQL is the language of choice for accessing databases on many other platforms. It is the only language for distributed databases and heterogeneous systems.

Data description specifications (DDS)

Externally described files can be described with DDS. DDS provides descriptions of the field-level, record-level, and file-level information.

You might use DDS because it provides the most options for the programmer to describe data in the database. For example, only with DDS can you describe key fields in logical files.

The DDS form provides a common format for describing data externally. DDS data is column sensitive. The examples that follow have numbered columns and show the data in the correct columns.

After a database file is described, you can view the description.

• Describing database files using DDS
  When you describe a database file using data description specifications (DDS), you can describe the file at the file, record-format, join, field, key-field, and select/omit-field levels.

• Specifying database file and member attributes
  When you create a database file, database attributes are stored with the file and members. You specify attributes with database command parameters.

 

Parent topic:

Creating and describing database files

 

Related concepts

IDDU Use PDF
SQL programming
SQL reference
Displaying information about database files