ALLBASE/SQL

ALLBASE/SQL is designed for HP 3000 900 Series systems. ALLBASE/SQL con tains both a network model database managemen t system, called TurboIMAGE, and a relational model database managemen t system, called HP SQL. It has been optimized for MPE/iX systems.

HP SQL, the relational model database managemen t system used when MPE/iX is running in Native Mode, is discussed in the subsection belo w. TurboIMAGE/XL is discussed later in this chapter.

HP SQL

HP SQL is the relational model database managemen t system (DBMS) module of ALLBASE/SQL. (Table 7-1 shows ALLBASE/SQL speci￿cations useful to programmers. F or detailed information on ALLBASE/SQL componen ts, refer to the Data Managemen t Series.)

HP SQL allows views to be created. A view is a table deriv ed by de￿ning a ￿lter o ver one or more tables to let users or programs view only certain data in the tables. Views impro ve security by allowing users to access only the data they ha ve a need to know. Since the view is not actually a physical table, use of views does not result in redundan t data. When data in a table is updated, all views that use the data are automatically updated.

An HP SQL query requires that the programmer specify only the data needed, minimizing the amount of preplanning and coding necessary . A non-procedural in terface allows the query of HP SQL databases without specifying data access path information. Y ou can operate on entire sets of data at one time, rather than on one record at a time. The major features of HP SQL are:

Relational data model allows y ou to specify required data, without specifying the retriev al method.

Language preprocessors allo w the same statemen ts that are used for an in teractive query to be embedded in HP Pascal/iX and HP COBOL II/XL application programs.

Concurrent access allows multiple users to sim ultaneously access data.

Speci￿cation of lev els of access privileges main tain security for users and groups of users.

Data independence allows y ou to make changes to the database structure without requiring modi￿cation of applications.

You can de￿ne views that allow a user or group of users to see parts of one or more tables as a single, virtual, table. These act as a ￿lter to customize a table.

Query optimizer reduces requiremen t for query planning details.

B-tree indexes support fast data access.

User controlled transactions ensure that data is alwa ys in a consistent state.

Automatic locking ensures data in tegrity in a multiuser environment by preventing access to data while it is being updated.

Automatic rollbac k recovery preserves logical data in tegrity due to a soft crash.

You can invoke rollback capability in a program to allo w erroneous data, usually generated in an on-line situation, to be remo ved before the transaction is completed.

7-6 Data Management