HP 3000 Manuals

HP System Dictionary XL Gen. Ref. Vol. 1

Sharing Attribute Values 

To prevent some of these non-standardization problems, and to allow you
to create smaller dictionaries that are easier to maintain, System
Dictionary allows you to create entities and relationships in a local
domain version and link them to existing entities or relationships of the
same type in the common domain version.  The linked occurrences will then
share the attribute values (and the memory storage space) of the
occurrences they are linked to.

For example, a Dictionary Administrator wants all last names described in
the dictionary to be 32 characters long, and therefore creates an entity
called LAST-NAME of type ELEMENT in the common domain version, setting
the value of its attribute BYTE-LENGTH, to 32.  The DA then instructs the
dictionary users to use this entity for all last names.  User #3,
however, needs to call the entity by a different name, creates an entity
called CUSTOMER-LAST-NAME and links it to the entity LAST-NAME in the
common domain version.  The entity CUSTOMER-LAST-NAME (the local entity)
now shares the attribute value (32) of the attribute BYTE-LENGTH of the
entity LAST-NAME (the common entity).  Note that the names of the two
linked entities do not have to be the same.

The linking feature, therefore, promotes standardization within the
dictionary, and allows you to save space by using the same set of
attributes for multiple entities or relationships.  It also makes the
dictionary simpler and easier to maintain by having only one set of
attributes to modify, etc.  for a set of linked occurrences, instead of
several separate sets.  Figure 4-4 below illustrates the common domain
and one local domain, which contain common version CV1 and local version
LV1 respectively.  The local version LV1, which is linked to the common
version CV1, contains local entity LE1 and local relationship LR1, which
are linked to common entity CE1 and common relationship CR1 respectively,
in the common version.  Note that entities called E2 in both the common
and local domains are not linked.  They are therefore completely separate
entities, and do not share the same attributes, even though they have the
same name.  Remember that you must link the local domain version to the
common domain version before you can link occurrences they contain.
(Linking versions is explained on the previous page.)


          Figure 4-4.  Linking Occurrences Between Domains 

Special Attribute Values 

A local domain occurrence shares all the attribute values of the
occurrence it is linked to in the common domain, except for the values of 
its special attributes.  (Special attributes are introduced in Chapter
3.)  The values of the special attributes of the local domain occurrence
are allowed to differ from those of the occurrence in the common domain,
so that they will describe the linked occurrence in the local domain.
This exception is necessary because System Dictionary assigns values to
these attributes based on the event in which you create them.

For example, the attribute date-created, describing a linked occurrence
in a local domain, contains the date on which the linked occurrence was
created, not the date on which the occurrence in the common domain was
created.  The values of the scope-changed, and date-changed attributes
are handled the same way.  The values for the attributes scope-owner and
sensitivity are allowed to vary so that the users of each domain have
control over these security attributes.  The value of the id-number
attribute assigned to an entity is arbitrary, so there is no need to keep
it synchronized between occurrences.  The relationship-position attribute
assigns ordinal numbers to a set of relationships of the same type that
have the same parent entity.  The ordinal numbers implicitly define the
order in which the child entities of these relationships occur within the
parent entity.  For example, in a series of relationships of the type
RECORD contains ELEMENT that have the same RECORD entity, the
relationship-position attribute implicitly defines the ordering of
elements within the record.  You can vary relationship-position attribute
values among linked relationships so that users in each domain can
re-arrange their order.  The relationship CUSTOMER-ADDRESS contains
LAST-NAME, for example, may be linked between domains.  But in one
domain, its relationship-position value may indicate that LAST-NAME comes
first in the record while in another domain it may come last.

MPE/iX 5.0 Documentation