| SAS/ACCESS Interface to CA-IDMS Software: Reference |
CA-IDMS enables you to build one or more databases using
a data dictionary. A data dictionary is itself a CA-IDMS database
that contains all the data and system definitions for one or more databases.
A data dictionary is divided logically into areas. The
information is organized into entity types, which correspond to the main data
processing components, such as elements, records, files, programs, and users.
Data dictionaries monitor most aspects of the database environment, from
tracking the status of terminals, systems, and users to being a central resource
of information about the system and providing security. Some large information
systems use multiple dictionaries; for example, a system may have one dictionary
for each division of a company.
A database administrator (DBA) manages
and maintains the data dictionaries and the entire CA-IDMS system. DBA duties
often include programming systems, managing resources, monitoring the system's
performance, and overseeing its security. The DBA has a key role in the SAS/ACCESS interface
to CA-IDMS, which is explained in more detail in this chapter.
Within a CA-IDMS data dictionary are the definitions
for a database's schema and subschema. A schema describes the
contents and structure of a single database, including all of the records
and sets that are necessary to define its data elements and data relationships.
A subschema is a subset of a schema that
is used by programs at runtime. It consists of all the data elements, records,
sets, and areas that are defined in the schema or a subset thereof. It includes
database records and can include logical records as well as logical-record
paths (defined below). The DBA defines logical records and their paths in
the subschema before application programs are coded and executed.
Data Dictionary, Schemas, and Subschemas
illustrates the relationships among the data dictionary, schemas, and subschemas.
Data Dictionary, Schemas, and Subschemas
![[IMAGE]](./images/01328076.gif)
CA-IDMS provides two operating environments, or modes,
for accessing data dictionaries and databases. In the central version, multiple concurrently executing programs access the database(s) through
one shared copy of the database management system (DBMS). The central version
controls concurrent updating of the database by multiple users in order to
maintain database integrity.
In local mode, one program at a time accesses
the database through a dedicated copy of the DBMS. You cannot run local mode
against a database at the same time that the central version is accessing
it.
A Distributed Database System (DDS) distributes
data storage and processing functions among several systems. These systems
can execute on one or more machines and at one or more sites. Each system
is a node in the DDS configuration. A central version specifies which node
within the DDS system to access.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
