iX V6.5 (30391-90011)

36 Chapter2

Database Structure and Protection

Database Elements

Data Sets

A data set is a collection of data entries where each entry contains values for the same

data items. For example, a customer data set can contain entries composed of the same

nine data items: ACCOUNT, LAST-NAME, INITIAL, STREET-ADDRESS, CITY, STATE,

ZIP, and CREDIT-RATING. Normally, each data set is associated with some real-world

entity, such as orders, customers, employees, and so forth.

A database can contain up to 199 data sets. Each data set is referenced by a unique data

set name that follows certain naming conventions. The data set names are made up of the

root ﬁle name appended by two characters. For example, if the root ﬁle is named XXXX,

the ﬁrst data set deﬁned in the schema is named XXXX01, the second data set is named

XXXX02, and so on. To name the maximum of 199 data sets per database, names are

incremented from XXXX01-99, XXXXA0-A9, XXXXB0-B9, up to XXXXJ9.

If the data set is a jumbo data set, the additional ﬁles created for the data set are named

by appending POSIX extensions such as .001, .002, and so on to the data set name. For

example, if the jumbo data set XXXX02 requires two additional ﬁles, they are named

XXXX02.001 and XXXX02.002. The additional ﬁles are called chunks.

Each data set is stored in one disk ﬁle, or more if a jumbo data set, consisting of storage

locations called records. When you describe the database with the database deﬁnition

language, you specify the maximum capacity, or number of records, of each data set. Each

record is identiﬁed by a record number that can be used to retrieve the entry within it.

Figure 2-1. shows a sample of one data set from a database named ORDERS which will be

used as an example throughout this manual. The data set is named CUSTOMER. The

information in this data set pertains to the customers of a business. All the data about a

particular customer is contained in a data entry. Each piece of information such as account

number or last name is a data item. Many data item values can be referenced by the same

data item name if each value exists in a different data entry. For example, the data item

FIRST-NAME has the value JAMES in one data entry and ABIGAIL in another data

entry.