NonStop Systems Introduction

The Relational Database Management System
NonStop Systems Introduction—527825-001
4-14
Active Data Dictionary
Active Data Dictionary
SQL/MX uses a special set of tables to record the definitions of all objects that belong
to a particular database. This set of tables is called the SQL catalog. The catalog
records the definitions of all the database tables in a TABLES table, the definitions of
views in a VIEWS table, the definitions of indexes in an INDEXES table, the definitions
of programs that access SQL objects in a PROGRAMS table, and so on.
The SQL/MX data dictionary is the collection of all the SQL catalogs on a particular
system or network. If you think of each SQL catalog as a repository of information
about a particular database, you can think of the SQL data dictionary as a repository of
information about all the databases on your system or network.
The SQL data dictionary is an active dictionary. This means that the definitions of SQL
objects in the SQL catalogs always match the actual state of the objects. For example,
if you enter a data definition statement that adds a new column to a table, this new
column definition automatically becomes associated with the table definition in the
catalog. With an active dictionary, you do not run into situations where your database
tables have columns of data or partitions or indexes that are not represented in the
catalog.
An active data dictionary benefits your applications in two ways:
•
When you add definitions for tables, columns, indexes, and other objects, new
applications can begin to use the new definitions right away.
•
Existing applications can continue to run without changes to source code. The
data access portion of each program affected by a new definition is automatically
recompiled in production.
SQL/MX provides a convenient facility for documenting the objects recorded in the
data dictionary. The COMMENT command allows the database administrator to enter
comments about tables, views, indexes, and other SQL objects in the COMMENTS
table of the SQL catalog.
SQL/MX Support for Decision Support and
Data Mining
SQL/MX supports the traditional and Object-Relational Data Mining (ORDM)
approaches to data mining. An overview of these two approaches follows. For details,
see the SQL/MX Data Mining Guide.
Traditional Approach
Traditional decision support applications emphasize extracting information from the
database through queries. The database queries are typically made directly from a
workstation or PC. SQL/MX supports the use of off-the-shelf workstation and PC-
based client tools for database queries.