1. Cognos 8 Training Session
Saravanan Vajjiravel

2. Agenda Data Warehouse Overview Cognos 8 Overview
Cognos 8 Framework Manager
Cognos 8 Report Studio
Cognos 8 Query Studio
Cognos Work Approach – Telstra
Case Study
Q/A

3. Data warehouse Overview

4. Data Warehouse
Data warehouse is a process for building decision support systems and knowledge management environment that supports both day-to-day tactical decision making and long-term business strategies. 
Bill Inmon "Subject-oriented, integrated, time variant, non-volatile collection of data in support of management's decision making process."

5. DW Methodologies Top-Down Bottom-Up Practitioner Bill Inmon
Ralph Kimball
Emphasize
 Data Warehouse
Data Marts
Design
Enterprise based normalized model; marts use a subject orient dimensional model
Dimensional model of data mart, consists star schema
Architect
Multi-tier comprised of staging area and dependent data marts
Staging area and data marts
Data set
DW atomic level data; marts summary data
Contains both atomic and summary data

6. Star schemas
The following figure shows a star schema with a single fact table and four dimension tables. A star schema can have any number of dimension tables. The crow's feet at the end of the links connecting the tables indicate a many-to-one relationship between the fact table and each dimension table.

7. Snowflake schemas
The following figure shows a snowflake schema with two dimensions, each having three levels. A snowflake schema can have any number of dimensions and each dimension can have any number of levels.

8. Star vs. Snowflake Snowflake Schema Star Schema Which Data warehouse?
Good to use for small data warehouses/data marts
Good for large data warehouses
Normalization(dim table)
3 Normal Form
2 Normal Demoralized Form
Ease of Use
More complex queries and hence less easy to understand
Less complex queries and easy to understand
Ease of maintenance/change
No redundancy and hence more easy to maintain and change
Has redundant data and hence less easy to maintain/change
Query Performance
More foreign keys-and hence more query execution time
Less no. of foreign keys and hence lesser query execution time

9. Types of Facts There are three types of facts:
Additive: Additive facts are facts that can be summed up through all of the dimensions in the fact table.
The purpose of this table is to record the sales amount for each product in each store on a daily basis. Sales_Amount is the fact. In this case, Sales_Amount is an additive fact, because you can sum up this fact along any of the three dimensions present in the fact table -- date, store, and product. For example, the sum of Sales_Amount for all 7 days in a week represent the total sales amount for that week.
Date
Store
Product
Sales_Amount
Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others.
Non-Additive: Non-additive facts are facts that cannot be summed up for any of the dimensions present in the fact table.
The purpose of this table is to record the current balance for each account at the end of each day, as well as the profit margin for each account for each day.
Current_Balance is a semi-additive fact, as it makes sense to add them up for all accounts (what's the total current balance for all accounts in the bank?), but it does not make sense to add them up through time (adding up all current balances for a given account for each day of the month does not give us any useful information). Profit_Margin is a non-additive fact, for it does not make sense to add them up for the account level or the day level.
Date
Store
Current_Balance
Profit_Margin

10. Types of Fact Tables Cumulative:
This type of fact table describes what has happened over a period of time. For example, this fact table may describe the total sales by product by store by day. The facts for this type of fact tables are mostly additive facts. The first example presented here is a cumulative fact table.
Snapshot:
This type of fact table describes the state of things in a particular instance of time, and usually includes more semi-additive and non-additive facts. The second example presented here is a snapshot fact table.

11. Junk Dimension / Degenerate Dimension
Junk dimensions are dimensions that contain miscellaneous data (like flags and indicators) that do not fit in the base dimension table.
Degenerate Dimension:
A degenerate dimension is data that is dimensional in nature but stored in a fact table. For example, if you have a dimension that only has Order Number and Order Line Number, you would have a 1:1 relationship with the Fact table. Do you want to have two tables with a billion rows or one table with a billion rows. Therefore, this would be a degenerate dimension and Order Number and Order Line Number would be stored in the Fact table.

12. Questions & Answers
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