Data Definition Language (DDL) Reference Manual (G06.24+)

Data Definition Language (DDL) Reference Manual—426798-002
1-1
1 Introduction to DDL
The Data Definition Language (DDL) product enables you to define data objects in
Enscribe files and to translate these object definitions into source code for
programming languages and other products on HP NonStop systems.
The DDL language has statements to define data objects and commands to control
how the statements are compiled. DDL data objects include the following:
•
Constants
•
Definitions (for single fields and groups of fields)
•
Records
•
Subsystem Programmatic Interface (SPI) token codes
•
SPI token maps
•
SPI token types
The DDL program compiles object definitions and generates any requested output
from the compiled definitions. Depending on which compiler commands you enter, DDL
builds a dictionary from the definitions, translates the definitions into File Utility
Program (FUP) commands, or generates object-definition source code in one or more
programming languages.
A DDL dictionary acts as a repository for the DDL definitions. It helps to maintain
consistency so that the same data, regardless of where it is used, is described in the
same way. Although commonly used to describe data in a database, a DDL data
dictionary can be used to describe other kinds of data. For example, Transfer
applications generally use DDL to define and maintain units-of-work. An application
can have more than one dictionary, or the application can maintain all of its data in a
single dictionary. The only restriction is that only one dictionary can reside on a
subvolume.
Subsystems that define SPI messages in a Distributed Systems Management (DSM)
environment must define the SPI message tokens with DDL, optionally add them to a
dictionary, and compile the definitions into C, COBOL, Pascal, pTAL, TACL, or TAL
code.
This section provides an overview of DDL functionality, including compiling and
translating data definitions, using DDL definitions, creating a data dictionary, creating a
database, generating source code, maintaining a dictionary, and examining a
dictionary.
Compiling and Translating Data Definitions
DDL performs two main functions:
•
Compiling statements that define data objects
•
Translating compiled definitions into source code for host languages and FUP
DDL also generates reports on the contents of a DDL dictionary. All DDL statements
and commands are passed as input to the DDL compiler input can be from a source