Introduction to Data Management

Accessing Databases With NonStop SQL
3-6 15873 Tandem Computers Incorporated
Special commands that manage concurrent access to the database, maintain the
latest statistics about the database, and create constraints, which are rules that
apply to data values added to the database
Physical database design extensions such as distributed databases, tables audited
by TMF and nonaudited tables, specification of blocksize and other physical
attributes, and default locking of tables and rows
Relationship to Other
Products
NonStop SQL is integrated with the GUARDIAN 90 operating system. Specifically,
NonStop SQL interacts with:
The file system and the DP2 disk process to promote overall application
performance
The naming system to provide a uniform way of handling object names
The security system to guard the security and privacy of the database
NonStop SQL uses the EXPAND network software to manage the distribution of data
across networks of systems. This integration allows data to be accessed with equal
ease whether the data is stored on one or many systems, and whether those systems
are local or geographically remote.
NonStop SQL can be used with PATHMAKER and PATHWAY to increase
programmer productivity during application development and management, and
with TMF to ensure database consistency.
NonStop SQL can be used by the MEASURE data collection system to collect and
examine performance statistics on processes and tables, and to generate reports.
Tables, Views,
and Files
When you access your database, you refer to logical objects—tables and views, and
columns within those tables and views. These logical objects, of course, have physical
representations that reside in physical files. These objects and their underlying
physical files are described next.
Tables A relational table, as explained in Section 1, consists of columns (fields) that you
access by column names and rows (records) that you access by other specifications.
Kinds of Tables
In NonStop SQL, tables can have any of three organizational structures that determine
how rows (records) within them are ordered: key-sequenced, relative, and entry-
sequenced. Within these tables, each row is identified by a unique value called the
primary key; this ensures that each row is unique. In your NonStop SQL statements,
you select rows by referring to the contents of any columns.