TurboIMAGE/XL Data Base

A database is a collection of logically related data in one or more ￿les. The ￿les con tain both the data itself and structural information on ho w one piece of data relates to another. Pointers in the database allo w access to the actual data and indexing across the m ultiple ￿les in the database. A net work database ties together ￿elds con taining information that ma y be relevant to a single transaction ev en though they physically reside in di￿eren t records.

The terminology used to describe a database di￿ers from that used to describe MPE/iX ￿les. Table 7-2 shows the corresponding terms.

Table 7-2. Data Base Terminology

MPE/iX

Network Data Base

Relational Data Base

 

 

 

￿eld

data item

column

record

data entry

row (or tuple)

￿le

data set

table

￿le de￿nition

schema

- - -

collection of ￿les

database

database

application

database applications

database

 

 

environment

 

 

 

A network database consists of data sets. The structure of the database is a sc hema, which the user writes. The sc hema is processed and k ept in a special ￿le called a root ￿le, whic h is also part of the database. The term database application refers to a complete data processing application using a database managemen t system and a database.

The database described in this c hapter is a TurboIMAGE/XL data base. A TurboIMAGE/XL database has two types of data sets:

Detail set, whic h is a collection of related data en tries, each of which contains one or more a forward pointers, one or more bac kward pointers, and the data itself. A standalone data set contains no pointers. TurboIMAGE/XL uses the poin ter information to tie together all data entries whose searc h items have the same value.

Master set, whic h maintains indexing in to detail data sets or in to itself, if it is a man ual master set. Indexing consists of a k ey data item.

A given network database can ha ve many detail sets and man y master sets.

A key data item is frequen tly called simply a k ey item. It uniquely iden ti￿es the related data entries in a master data set. A searc h item value is not necessarily unique. In a master set, a key item is the data item used to perform the searc h.

Data Management 7-11