TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

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 240 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 240 data sets per database, names are
incremented from XXXX01-99, XXXXA0-A9, XXXXB0-B9, up to XXXXO0.
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.