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

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2 Dictionary Concepts
Overview
This chapter provides a basic description of System Dictionary. More details are provided in chapters 3, 4,
and 5.
Entity-Relationship Model
System Dictionary uses a simple but powerful entity-relationship (E-R) model in which the central
components are entities, relationships between entities, and attributes that define and characterize
entities and relationships. You can use the System Dictionary E-R model to describe the real-world objects
of an information network, and to define logical connections between these objects.
Entities and Relationships
Entities and relationships are the definitions that are stored in and retrieved from the dictionary. Entities
are dictionary definitions that refer to objects in the real world of an information network. An entity has
attribute values that further define the real-world object or that describe the entity itself. A relationship is
an ordered list of entities. Relationships express logical connections between real-world objects. Most
relationships involve two entities and are called binary relationships. System Dictionary also supports N-
ary relationships involving three to six entities. Relationships have attribute values that in some cases
describe the dictionary definition itself and in other cases describe one of the entities in the relationship.
Therefore, you can use relationship attribute values to document an entity in a particular context or usage.
Structures
The System Dictionary E-R model provides a set of structures that support the creation and retrieval of
entities and relationships. Entity types are structures that define, categorize, and qualify entities. For
example, IMAGE-DATABASE is a System Dictionary entity type that defines entities that describe
IMAGE databases. Relationship types are structures that define, categorize, and qualify relationships.
IMAGE-DATABASE contains IMAGE-DATASET is a System Dictionary relationship type that defines
relationships between an IMAGE database and data set.
Attributes are structures that define the attribute values of entities and relationships. IMAGE-DATASET-
TYPE is a System Dictionary attribute associated with the IMAGE-DATASET entity type. CAPACITY is
an attribute associated with the IMAGE-DATABASE contains IMAGE-DATASET relationship type.
In System Dictionary, each entity type and relationship type has an attribute list. Attributes are
associated with the entity type or relationship type by a structural component called a type-attribute
association. When an attribute is associated with an entity type or relationship type, each entity or
relationship of that type must have a value for the attribute.
System Dictionary supports six attribute types. Five of the types are fixed-length:
• Alias--A 32-byte character value
• Boolean--A 1-byte true or false value
• Character--A 1 to 255-byte, inclusive, alphanumeric value
• Floating--A 32-bit or 64-bit floating-point format
• Integer--A 16-bit or 32-bit binary value