My first Publication Agile-Data-Warehouse-Design-eBook | Page 309

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Appendix B
D
Dn Date data type. The numbered version is used in duration formulas for
derived facts; for example, Project Duration DF=D2-D1. Numbering
can also denote chronological order of milestones within an evolving event. 5, 8
T
Tn Text. Long character data used to hold free format text. The numbered
version is used to define the maximum length. Overrides the default length. 5
B Blob. Binary long object used to hold documents, images, sound, objects,
and so on. 5
Key Types
C ODE M EANING /U SAGE
C HAPTERS
PK Primary Key. Column or group of columns that uniquely identify each row in
a table. 5
SK Surrogate Key. integer assigned by the data warehouse as the primary key
for a dimension table. Used as a foreign key in fact tables.
Used to denote that example data in a BEAM ✲ table column will be replaced
by an integer foreign key in the physical model. 5
BK Business Key. A source system key. NK Natural Key. A (source system) key used in the real world 5
FK Foreign Key. A column that references the primary key of another table. 5
RK Recursive Key. A foreign key that references the primary key of its own
table. Often used to represent variable-depth hierarchies. Stores information
needed to build hierarchy maps; for example, Parent Company Key in
Company. 6
3, 5
Dimensional Attribute Types
C ODE M EANING /U SAGE
C HAPTERS
CV
CVn Current Value attribute. A dimensional attribute that holds the current value
only. Source system updates overwrite the previous value. Supports current
value (as is) reporting. Also known as a type 1 slowly changing dimensional
attribute.
The numbered version relates a CV attribute to a previous value (PV) version
of itself; for example, Territory CV1 and Previous Territory PV1. 3, 6
HV
HVn Historic Value attribute. A dimensional attribute that tracks historical values.
Source system updates cause a new version of the dimensional record to be
created, preserving the historically correct values. Supports historical value
(as was) reporting. Also known as a type 2 slowly changing dimensional
attribute.
The numbered version is used in combination with CV to define conditional
HV attributes. These are CV attributes that act as HV attributes only when
another HV attribute with the same number changes; for example, Street
CV, HV1 will only track changes when Zip Code HV1 changes at the same 3, 6