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University of California, Davis

Application Development Methodology

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Techniques

Attribute Type and Domain Definition Technique

Rules

• Diagramming Conventions for Attribute Types
• Diagramming Conventions for Identifiers
• Attribute Type Examples
• Attribute Type Naming

Rules: Diagramming Conventions for Attribute Types

When you feel that it is useful to annotate an entity relationship diagram to show a few significant attribute types of an entity type, list the attribute types below the entity type name in smaller letters, omitting the entity type name part of the attribute type.

Rules: Diagramming Conventions for Identifiers

Any names of identifying attribute types that are added to entity type boxes are highlighted with an asterisk. Relationships, when memberships are used to identify entities of the plural membership, have an "I" placed on the relationship line close to the identified entity type. The "I" signifies that one or more attribute types of the single entity type may be a foreign identifier for the plural entity type. This is shown below:

Rules: Attribute Type Examples

Rules: Attribute Type Naming

Attribute Type Constraints

An attribute type must describe one and only one entity type. The complete set of attribute types must be non-redundant in name and meaning.

Attribute Type Naming Conventions

Structure of attribute type names

Attribute type names reflect the name used in the business. They should follow this structure:

* Entity type name or subtype name (if necessary to avoid ambiguity), ignoring the possessive case

* Qualifier(s), indicating the description or purpose (a noun or noun phrase, a plural noun for multi-valued attribute types); used to provide uniqueness and clear meaning

* Domain name, where appropriate or necessary

Abbreviated attribute type names should not be used because they cause confusion. An abbreviated name used by the business is recorded as a synonym.

Attribute type names can typically be turned into a descriptive phrase by reversing the order of the words and inserting "of" between each word. For example, Employee Birth Date becomes Date of Birth of Employee.

Examples of attribute type names

* Employee (entity type name) Birth (description) Date (domain)

* Course Fixed Price

* Product Short Description

* Lecturer (entity type name) Skills (multi-valued description)

Clarity of attribute type names

Note that an attribute type name should either be qualified to remove any ambiguity over its meaning, or it should be associated with a domain that is itself named unambiguously. For example, giving Employee Height a value of 72 without a unit of measure is not informative. However, Employee Height in Inches = 72 is meaningful and can be manipulated by standard means or can be readily translated into other usable measures (72 inches = 183 centimeters).