iX V6.5 (30391-90011)

Chapter 2 41

Database Structure and Protection

Data Set Types and Relationships

Manual versus Automatic Data Sets

Database designers can choose a manual or automatic master data set depending on the

following:

• Manual masters help ensure that valid search item values are entered for related detail

entries. They can also serve as indexes to detail data sets.

• Automatic masters serve as indexes to detail data sets and save time when the search

item values are unpredictable or so numerous that manual addition and deletion of

master entries is undesirable.

Whenever a single data item is sufﬁcient for a master data set, the database designer must

decide between the control of data entry available through manual masters and the

program simplicity offered by automatic masters. For example, because DATE-MASTER is

an automatic data set, erroneous dates such as 331299 can be accidentally entered.

Detail Data Sets

Detail data sets have the following characteristics:

• They are used to record information about related events such as information about all

sales to the same account.

• They allow retrieval of all entries pertaining to a uniquely identiﬁable entity. For

example, account number 95430301 can be used to retrieve information about all sales

made to Ms. Brighton.

• They can be deﬁned with from zero to 16 search items (unlike a master data set which

contains at most one key item). The values of a particular search item need not be

unique. Generally, a number of entries will contain the same value for a speciﬁc search

item.

• They can be deﬁned for automatic expansion of their capacity.

The SALES data set contains four search items: ACCOUNT, STOCK#, PURCH-DATE,

and DELIV-DATE. Two entries in the example in Figure 2-3. have identical values for the

ACCOUNT item in the SALES data set. TurboIMAGE/XL stores pointer information with

each detail data entry that links all entries with the same search item value. Entries

linked in this way form a chain. A search item is deﬁned for a detail data set to retrieve all

entries with a common search item value (that is, all entries in a chain). The SALES

entries with ACCOUNT equal to 95430301 form a two-entry chain. The number of entries

in a single chain is limited only by the maximum number of entries in a data set.

Paths

A master data set key item can be related to a detail data set search item of the same type

and size. This relationship forms a path. A path contains a chain for each unique search

item value. In Figure 2-3., the ACCOUNT key item in CUSTOMER and the ACCOUNT

search item in SALES form a path to link the CUSTOMER master data set to the SALES

detail data set. One chain links all SALES entries for account number 95430301. The

chain for account number 12345678 consists of one entry. Both chains belong to the same

path.