Analyzing Data › Defining Entity Types, Relationships, and Attributes › Defining Entity Type Attributes › Attribute Source Category

Attribute Source Category

An attribute fall into one of four source categories:

• Basic—The values of the attribute are intrinsic to entities of the entity type being described and cannot be deduced from the attribute values of other attributes or the existence of relationships.
• Derived—The values of the attribute are always deduced or calculated from the values of other attributes or the existence of relationships.

  Note the word always. For example, the value of the attribute ORDER ITEM Price may have been initially derived using the then current PRODUCT Price. However, it is not repeatedly re-evaluated in the same way whenever PRODUCT Price is modified. This attribute value is not treated as derived.

• Designed—The enterprise invents the attribute to overcome some sort of business constraint or to simplify a system operation. The attribute value is derived in some way, such as a numerically increased serial number.
• Auto Number—The DBMS of the application generates the value of an auto number attribute automatically. An auto number attribute must be a whole number with no decimal places.

CA Gen treats designed attributes as if they were basic.

CA Gen treats derived attributes differently. Values are never merely set to some value; they must be derived using a calculation that is called a derivation algorithm that is assigned to the attribute as part of its definition.

Note: For more information, see Derivation Algorithm.

As an example, the likely source categories of attributes for the entity type CUSTOMER are listed in the following table.

Status and Credit Rating are considered to be either designed or derived, under differing conditions.

Credit Rating could be basic if its value is determined outside the organization, for example, by a credit agency.

Credit Rating could be derived if it is given a value by the business as the result of a specified calculation, or if it is subject to tightly specified rules. However, if it is the result of a less formally specified judgment, it is designed.

Outstanding Orders Value for a particular CUSTOMER entity is assumed to be the sum of the Amounts (an attribute) of all ORDERs (an entity type), which are placed by (a relationship membership) that CUSTOMER. So, its value depends wholly on the values of other attributes and relationship memberships. If the customer places a new order, causing a new pairing that is based on places/is placed by, the value of Outstanding Orders Value is likely to change. If the Amount of any order that is placed by the customer is modified, the value of Outstanding Orders Value change. Outstanding Orders Value is therefore a derived attribute.