Introduction to Data Management

4 Managing Records
With ENSCRIBE
15873 Tandem Computers Incorporated 4-1
The first generation of database management software from Tandem was based on the
ENSCRIBE database record manager and its associated products, the Data Definition
Language (DDL), ENABLE program generator, and ENFORM query language. Later,
the PATHMAKER online application code generator was added to this group of
software products. Today, these products continue to support applications and
relational databases at sites throughout the world.
The GUARDIAN 90 operating system services I/O requests from running programs
by transferring records between I/O devices and main memory using either
ENSCRIBE or NonStop SQL. If an application program directly accesses one of the
file types supported by ENSCRIBE, the operating system manages this access through
ENSCRIBE. If an application program refers to a NonStop SQL table, the operating
system uses NonStop SQL to access the table. In some cases, an application will use
both ENSCRIBE and NonStop SQL; ENSCRIBE calls and NonStop SQL statements can
coexist in the same program and even in the same transaction.
Although NonStop SQL is the recommended database management system for new
applications and databases, there are still circumstances when you will want to use
ENSCRIBE. You need ENSCRIBE, for example, when writing new programs that
access existing ENSCRIBE files or when modifying existing programs that already
rely on ENSCRIBE.
ENSCRIBE processes data on a record-by-record basis. Thus, when a program
requests ENSCRIBE records for processing, ENSCRIBE obtains the records from disk
files and passes them to the program one at a time. When the program is ready to
write the processed records back to secondary storage, ENSCRIBE moves the records
from main memory one at a time and transfers them to disk.
Features ENSCRIBE offers many features that support data management tasks for
programmers and database designers. The most important of these are described in
the next few pages.
Multiple Disk File
Structures
ENSCRIBE supports both structured and unstructured files on disk, giving you great
latitude in the way you access data in a relational database.
Structured files include key-sequenced, relative, and entry-sequenced files, as
introduced in Section 3. Each record in a structured file contains a set of fields.
Data transfers between an application and a structured file are handled in terms of
logical records and key fields within those records.
Key-sequenced files contain variable-length records stored in a sequence
based on primary key values that are unique for each record. The primary key
is simply a particular field, designated by the user. For example, in a key-
sequenced file that contains employee data, the primary key might be the field
that denotes employee identification numbers. In this file, the records for
employees 1001, 1002, and 1003 are stored in the ascending order of these
values.