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Realm concept Schema DDL
108 U929-J-Z125-9-76
4.10 The realm concept
In order to take the aspects of
– data privacy,
–data recovery,
– concurrent access, and
– the logical association of certain data
into account, it is often advisable to subdivide the database into subunits. These subdivi-
sions are called “realms” or “areas”. They are generated as BS2000 files at database
creation (see the “Creation and Restructuring” manual, Database creation). There are
realms which contain UDS/SQL-internal information only and realms for user data. The
latter are called user realms.
A maximum of 123 realms can be defined for a database with a page length of 2048 bytes
(2-Kbyte page format).
A database with a page length of 4000 or 8096 bytes (4-Kbyte or 8-Kbyte page format), by
contrast, may be subdivided into a maximum of 245 realms.
Data privacy
With the BPRIVACY utility, the database administrator can grant certain groups of users
access privileges to database objects (realms, record types, sets).
When defining the subschema, a user can restrict the use of data to certain realms.
Data security
The subdivision into realms allows the effects of hardware errors or read/write errors to be
restricted to a few realms or even to one realm. In such cases, only the realm or realms
concerned needs to be recovered by means of realm copies or after-images, if used (see
the “Recovery, Information and Reorganization” manual, BMEND). Data that is updated
frequently should therefore be stored in a separate realm from data that is seldom updated
or updated only at certain times.