ETL into a Time Variant Data Warehouse - Data Warehouse Designs - page 203

Hierarchy are attributes of Location; and Fail Rate and Skill Set are attri-
butes of Formula.
An attribute entity can be described or further defined by another
attribute entity. For example, Certification might be further described by
Certification Board, Accreditation Date, and Test Criteria. In that exam-
ple Certification Board is an attribute of Certification, which is an attri-
bute of Factory Worker. The same can also be true for all other entities.
The Raw Material entity is defined by its Supplier, which could be further
described by the Credit Terms of the Supplier. In this way an entity of
the enterprise can be both an entity and an attribute of an entity, and an
attribute of an entity can have its own attributes that are also entities of
the enterprise.
The role of a CDC function is to identify changes in each individual
entity and integrate those changes into the data warehouse. Table 13.1 dis-
plays the comparison performed by a CDC function. Obviously, a CDC
function does not operate on one Factory Worker, one Raw Material, one
Location, and one Formula. Instead, a CDC function focuses on all Factor
Workers, another CDC function focuses on all Raw Materials, another
CDC function focuses on all Locations, and another CDC function
focuses on all Formulas. The example here in Table 13.1 is presented in
this form for continuity throughout this chapter.
The “Change?” results for Factory Worker, Raw Material, Location, and
Formula are all equal to the value “n/a.” This happens because the Factory
Worker's name is Fred. Fred's name identifies Fred and is therefore the

tABle 13.1
Changed Data Capture

Dimension Attribute Previous Value Present Value Change?

Factory Worker Fred Fred n/a

Certification Cratsman Cratsman No

Safety Rating AA+ AA+ No

Raw Material Iron Ore Iron Ore n/a

Supplier Hess Ironworks Hess Ironworks No

Quality 95% 96% Yes

Location Atlanta Iron 35 Atlanta Iron 35 n/a

Geography Atlanta, GA Atlanta, GA No

Hierarchy Metals Metals No

Formula RWU987 RWU987 n/a

Fail Rate 4% 2% Yes

Skill Set Iron Cratsman Iron Cratsman No