The analysis at the third, or Entity-Relationship-Attribute, level combines the work of the framework level with that of the classification model and the data event maps by adding characteristic groupings determined inductively into a classification structure determined deductively, and by adding characteristics and or attributes to both the entities and the relationships. A characteristic or attribute is represented by a circle attached directly to the entity or the relationship which it describes. The circle contains the name of the attribute. Attributes might be: identification information, residence information, physical description, inventory status, packaging information, hobbies, clothing sizes, etc.
The attribute names for an employee entity, might be very similar to the section or item headings on an employment application, or the section or item headings on the permanent employee record form. For a customer, they might be very similar to the section headings on a new account opening form, or on the customer record form.
For an entity, each attribute represents some grouping of data which is necessary, from a business perspective, to describe a physical or logical characteristic of the entity, or to describe some activity of the entity. For a relationship, each attribute represents some grouping of data which is necessary from a business perspective, to describe, qualify or maintain the named relationship between two entities.
The Entity-Relationship-Attribute model is an expansion of the Entity-Relationship model. Until this point the models have only identified the entities and relationships by name and context. For a given entity or relationship little is known about them other than their name, the obvious fact of their existence, and the fact that the firm is interested in them.
At the Entity-Relationship-Attribute level, entities and relationships are described in terms of their attributes, or characteristics. In other words, beyond knowing that the entity exists, we must also know what the entity looks like, how it is identified, and what it does. These descriptors or characteristics are called attributes. An attribute is thus any distinct aspect of the entity or relationship that is necessary to describe the entity or to qualify the relationship. The full description of an entity or relationship consists of the full set of attributes which describe that entity or relationship.
For an entity attribute to be significant it must relate directly to the entity, be completely dependent on the entity for its existence and meaning, and it must be definable in terms of one or more data elements. It is immaterial as to whether there are one or more data elements in an attribute, as long as the attribute applies to all instances of the entity being represented. Seen another way, an attribute is some distinct category of mutually related data, the sum of which describes something of interest about the entity. The identifiers (unique or otherwise) of an entity are a special form of attribute.
Entity attributes represent:
A physical characteristic of that entity - size, shape, weight or color
An historical attribute - date of birth or date of hire
A location attribute - place of residence, place of work, or place of birth - A non-physical characteristic - price
An identifier - name, title
An occupational characteristic - current position, skill possessed, training received, educational courses, etc.
The intermediate or final results of some processing activities related to the entity
Data which relates to some current state or condition of the entity, or to some past or future state or condition of the entity
Data which relates to some current action taken by or against the entity, or to some past or future action taken by or against the entity
For an relationship attribute to be significant it must relate directly to the relationship, be completely dependent on the relationship for its existence and meaning, and it must be definable in terms of one or more data elements. It is immaterial as to whether there are one or more data elements in an attribute, as long as the attribute applies to all instances of the entity or relationship being represented.
Seen another way, an attribute is some distinct category of mutually related data, the sum of which describes something of interest, or some qualifier about the relationship between two entities. A relationship attribute must be dependent upon the connection between both entities and should be incapable of existence in the absence of that relationship. The minimum attributes of a relationship are the necessary identifiers of each entity of the related pair.
Relationship attributes represent some descriptor or qualifier of the relationship such as:
An historical attribute - date of marriage, or date of sale, date of storage
An location attribute - place of storage, place of work, or place of birth
A non-physical characteristic - price at time of sale, discount at time of sale, grade in course
Some meaningful data which is not an attribute of either entity participating in the relationship, but pertains only to the relationship between them. This data is sometimes called intersection data.
It is possible for the same named attribute to be used to describe many different entities and relationships. Identifier attributes in particular describe both the entities and the relationships between them.
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