Databases Reference
In-Depth Information
...
It [the DW] is the central point of data integration for business intelligence
and is the source of data for the data marts, delivering a common view of
enterprise data. (From
Mastering Data Warehouse Design
, by Claudia Imhoff,
Nicholas Galemmo, and Jonathon Geiger, John Wiley and Sons, 2003, pg.
400.)
Degenerate dimension
A single attribute dimension whereby the only
attribute is a reference identifier such as invoice number, P.O. number,
or transaction ID. This is needed to support analysis of the individual parts
of a business transaction (individual line items) and the entire business
transaction (the whole purchase order).
Derived attribute
An attribute that is created to facilitate the overall useful-
ness of the dimensional model. This enables different attributes to be pulled
together using a single identifier that can help the technical implementation
of the dimensional model. It is used when the underlying source systems do
not have a data element to uniquely define this case, and is required to pull
together nonrelated attributes of a junk dimension.
Derived fact
A fact that is calculated on-the-fly and not stored in the database.
Dimension
Major business categories of information or groupings
to describe business data. Dimensions contain information used for
constraining queries, report headings, and defining drill paths. Within a
dimension, specific attributes are the data elements that are used as row and
column headers on reports. Dimensional attributes are also considered to be
reference data. When describing the need to report information by region,
by week, and by month, the attributes following ''by'' are dimensions. Each
of these would be included in a dimension.
Dimensional model
A data model organized for the purpose of user under-
standability and high performance. In a relational database, a dimensional
model is a star join schema characterized by a central fact table with a
multi-part key. The components of this key are joined to a set of dimen-
sion tables, each defined by its own primary keys. In a multi-dimensional
database, a dimensional model is the database cube.
Dimensional modeling
A formal data modeling technique that is used to
organize and represent data for analytical and reporting use. The focus is on
the business perspective and the representation of data.
Entity-relationship (E-R) model
A data model that is used to represent data
in its purest form and to define relationships between different entities.
