HP System Dictionary/XL General Reference Manual Vol 1 (32256-90004)

3- 17
Figure 3-2. System Dictionary E-R Structure
Entities
Entities are dictionary definitions that refer to tangible objects in an information network. In System
Dictionary, an entity definition has three parts:
• An entity name --usually the name of a real object.
• The entity type, a dictionary category to which the entity belongs.
• Attribute values that further define and characterize the entity.
An entity is therefore a unique pairing of an entity name with an entity type. For example, to create a
dictionary definition of an IMAGE data base named ORDERS, you would need to create an entity named
ORDERS of entity type IMAGE-DATABASE. To define a VPLUS form named CUSTOMERS, you would
need to create an entity named CUSTOMERS of type FORM. If there is also an IMAGE data set named
CUSTOMERS, you would need to define an entity named CUSTOMERS of type IMAGE-DATASET. The
dictionary would then contain two CUSTOMERS entities, but they would be unique when qualified by
entity type FORM or IMAGE-DATASET.
Special Entity Naming
Entity names have the same restrictions as discussed in Chapter 2 under the Syntax discussion. Along
with those restrictions there are two reserved entity names. The two reserved entity names in System
Dictionary are the slash (/) and the question mark (?). These entity names have a special meaning in
creating or accessing relationships. You can use the slash name in a relationship to indicate a null entity.
You can use the question mark name in relationship retrieval to indicate that any entity name is
acceptable in a given position. Entity names may include slashes and question marks. The restriction is
that you cannot use them as entity names except in the relationship contexts just described. For example,
you cannot create an entity named ?, but you can create entities named ORDER?NUMBER or A/B.