Data warehousing theory and
modelling techniques
Building Dimensional Models
1. Matrix Method for getting
started.
2.
1.1 Build the Matrix
1.2 Use the four-step method
2. Managing the dimensional
Modelling Project.
2.1 Data Warehouse Bus Architecture Matrix
2.2 Fact Table Diagram
2.3 Fact Table Detail
2.4 Dimension Table Detail
2.5 Steps for the Modelling Team
2.6 Identifying the sources
2.7 using a Data Modelling Tool
Summary
1.1 Build the Matrix
 Table
Rows : Data Marts
 Table
Columns : Dimensions
Example Data Warehouse Bus Architecture Matrix
1.1 Build the Matrix
List the Data Marts (rows)
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Example: data marts for a telephone co.
– customer billing statements
– scheduled service and installation orders
– trouble reports
– marketing promotions
– call detail for a billing perspective
– customer inventory
– labor and payroll
– ...
1.1 Build the Matrix
List the Dimensions (columns)
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Example: Dimensions for the telephone co.
in data mart: Customer billing statement
– Time (date of billing)
– Customer
– Service
– Rate category
– Local service provider
– ...
Data Warehouse Bus Architecture Matrix
1.2 Use the four-step Method
to design Each Fact Table
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Step 1. Choose the Data Mart
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Step 2. Declare the Grain
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Step 3. Choose the Dimensions
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Step 4. Choose the Facts
Example: Telephone co.
Four-steps e.g.Telephone co.
1. Data Mart: Customer billing
 2. Grain: the individual line item on
each monthly customer bill
 3. Dimensions: Time, Customer,
Service, Promotion
 4. Facts: Line item amount,
Line item quantity
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2.2 Fact Table Diagram
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The fact table Diagram:
– Names the fact table
– Clearly states its grain
– Shows dimensions to which it is connected
– Shows all the other dimensions without
connections
Example : fact table diagram for the
telephone billing line item
 Example : Supporting information
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The telephone billing
Fact Table Diagram
Dimension information Table
Dimension Name
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Dimension Description
Supporting information for the Fact
Table Diagram includes the Name and
Description of each dimension
2.3 Fact Table Detail
Complete list of all the facts available
through the fact table
 List includes:
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– actual facts in the physical table
– derived facts presented through views
– facts calculated from first two groups
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Example: Customer billing Line item
fact table detail for the telephone co
Customer billing Line item
Fact table detail
2.4 Dimension Table Detail
Shows attributes in a single dimension
 Shows explicit grain of the dimension
 Shows the approximate cardinality of
each dimension attribute
 Shows hierarchies and relationships
between the attributes
 Example: Time dimension Table detail
 Example: Dimension attribute detail
descriptions
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Time Dimension Table detail diagram
Dimension attribute detail descriptions
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Documentation: Full descriptive
information to support the diagram
– Attribute Name, description, cardinality
– Slowly Changing Policy, Sample Values
Example: Time Dimension attribute
detail descriptions
Example: Many-to-many relationships and
slowly changing dimension attributes
Example: Correlated attributes
Time Dimension attribute
detail descriptions
Many-to-many relationships and slowly
changing dimension attributes
Correlated attributes
2.5 Steps for the Dimensional
Modelling Team
Create the Initial draft: data marts,
dimensions, data matrix and diagrams
 Track Base Facts
 Track derived Facts (Example)
 Present initial design to rest of IS team
 Select some key users to work on
project
 Present to Business users
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Derived Fact worksheet
2.6 Identifying the Sources for Each
Fact Table and Dimension Table
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Source. Name of the source system.
Business owner. Name of the primary contact within
the business who is responsible for this data.
IS owner. Name of the person who is responsible.
Platform. Operating environment where system runs.
Location. The actual location of the system. The city
and the specific machine where this system runs.
Description. A brief description of what system does
Example: Data Source Definitions
Example: Mapping data from source to Target
Data Source definitions
Mapping data from source to Target
Source-to-target data map:
Foundation for the development of the
data staging process
 To document specifically where the data
can be located
 Example: Sample Source-to-target data
map
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Sample Source-to-target data map (1/2)
Sample Source-to-target data map (2/2)
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Table name. The name of the logical table in the data warehouse.
Column name. The name of the logical column in the warehouse.
Data type. The data type of the logical column (char, number, date).
Length. The length of the field of the logical column.
Target column description. A description of the logical column.
Source system. The name of the source system where data feeds
the target logical column.
Source table/file. The name of the specific table or file where data
feeds the target logical column.
Source column/field. The name of the specific column or field where
data feeds the target logical column.
Data transform. Notes about any transformations that are required to
translate the source information into the format required by the target
column.
2.7 Using a Data Modelling Tool

Used to develop the physical data
model

Preferably one that stores your model’s
structure in a relational database
Summary (1/2)
Process used to apply dimensional
modelling techniques
 Bus Architecture Matrix to lay out the
data marts and dimensions
 Four-step method to design a single
data mart
 Diagramming techniques
 Data sourcing and mapping
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Summary (2/2)
 In
this section we focused on the
DATA
 Next:
different path of lifecycle
Technical architecture
Supporting Templates collected
on CD-Rom
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Template
Template
Template
Template
Template
Template
7.1
7.2
7.3
7.4
7.5
7.6
Data Mart Matrix
Dimensional Model Document
Derived Fact Worksheet
Logical table design
Data Source Definition Document
Source to Target Data Map