iX V6.5 (30391-90011)

38 Chapter2

Database Structure and Protection

Data Set Types and Relationships

Figure 2-2. Master and Detail Data Set Relationships

Master Data Sets

Master data sets have the following characteristics:

• They are used to keep information relating to a uniquely identiﬁable entity. For

example, the CUSTOMER data set contains information describing customers.

• They allow for rapid retrieval of a data entry because one of the data items in the entry,

called the key item, determines the location of the data entry. A key item cannot be a

compound item. In Figure 2-3. on the next page, the CUSTOMER data set contains a

key item named ACCOUNT. The location of each entry is determined by the value of the

customer's account number.

• They can serve as indexes to the detail data set (that is, they can be related to one or

more detail data sets). The ACCOUNT key item in the CUSTOMER master data set is

related to the ACCOUNT search item in the SALES detail data set in Figure 2-3. The

entry for a customer named Abigail Brighton with account number 95430301 serves as

an index to two entries in the SALES detail data set which contain information about

purchases she made.

Although there are unused storage locations in the CUSTOMER master data set,

TurboIMAGE/XL disallows any attempt to add another data entry with account number

95430301. The key item value of each entry must remain unique. The values of other data

items in the master data set are not necessarily unique because they are not key items and

are not used to determine the location of the data entry.