HP 3000 Manuals

HP System Dictionary XL Gen. Ref. Vol. 1

Linking Occurrences 

One of the major functions of a data dictionary is to ensure the
standardization and integrity of the definitions used in an information
system.  However, you can use the domain feature of System Dictionary to
unintentionally defeat this standardization.  You can create
"non-standard" dictionaries by creating identical occurrences in
different domains, or by creating occurrences in different domains which,
though not identical, should be.  For example, an entity named LAST-NAME
of type ELEMENT exists in four local domains.  Each entity was created by
a different user, and has a different value for one of its attributes,
BYTE-LENGTH. These different values mean that there is possibly no
standard length for last names described in the dictionary.  If these
differences are due to application requirements, the domain feature
serves a useful purpose, but if they are unnecessary, the domain feature
is allowing non-standardization, and its use should be looked at
carefully.

MPE/iX 5.0 Documentation