2. What is multidimensional model?
Logical view of the enterprise
Shows main entities of the enterprise
business and relationships between them
Not tied to a physical database and tables
Not E-R diagram
5. Attributes
Attributes are abstract items with
business relevance that are
created for convenient
qualification or summarization of
data on a report.
Attribute can also be defined as
column headings on a report that
are not a calculation
6. Attribute relationships
One to One
– Each customer has only one SSN.
One to Many
– Each customer can have several addresses.
Many to Many
– Each customer can buy many items, an item can be
purchased by many customers (item means SKU, not
the same physical object).
Many to One
– Several phone numbers can belong to one store, and
one store only.
7. Attribute relationships
Out of all relationships, Many to Many is the trickiest one.
If not modeled carefully, M;N can lead to double-counting
and other unhappy consequences.
Practical ways of dealing with M;N relationships:
– Create a relationship table
– Create a compound key
» Not advisable, but sometimes necessary
8. Hierarchies (Dimensions)
Hierarchies have the same meaning
as Dimensions in MicroStrategy 7.
Hierarchies are based on
relationships between Attributes.
They allow end users to define and
order groups of Attributes for display
and browsing purposes.
Time
Year
Quarter
Month
Day
9. Facts
Data columns (usually numeric) that can be used to perform
calculations needed to answer business questions.
Facts are stored in Fact Tables or Base Tables
Facts can be aggregated on different levels:
Aggregated on
Region level
Aggregated on
Country level
10. Facts (continued)
Same facts can be represented by different column name in the DW
due to various historical and design reasons.
In the example below the same fact has two different names: SALES
and DOLLAR_SALES
Facts are cross-dimensional, not limited to one dimension
only. In the example above, the same fact crosses two
dimensions: Geography and Time.
11. Facts (continued)
Facts are used to create metrics.
Metrics - business measurements (i.e. Dollar Sales, Units Sold, Gross
Margin and etc.) used by businesses to analyze and report their
performance.
Metrics are usually a fact that has a mathematical function applied to it
(sum, average, max, min and etc.)
More on metrics in a separate presentation
12. What to read for more information:
MicroStrategy 7 Project designer guide.
Have a good look at VMALL Data Model
– Identify attributes, hierarchies and facts – you’ll
need them for the Workshop.
