Why A Data Warehouse

What is a Data Warehouse ?

The conglomeration of an organization’s data warehouse staging and presentation areas, where operational data is specifically structured for query and analysis performance and ease-of-use.

Ralph Kimball, (2002) The Data Warehouse Toolkit.

Now in English

A data warehouse is a database organized in a way to allow for fast queries of information.

It contains the data from the different database systems that is brought together for a single view.

So what’s the difference ?

Transactional Sources

Centers around transactions

2 dimension reports

Age by System

Individual data

Slow

“ Cut-n-paste” into other applications

Data Warehouse

Centers around business facts

Multi-dimensional reports

Age by Race by Program

Aggregated data

Fast

3 rd party reporting tools can be used.

Measures Facts not Activities

Facts are business performance measurements

Meals provided

Dollars expended

Hours worked

Facts are numerical and additive

Sum of dollars spent

Count of clients served

Facts are stored to represent a measurement at a particular “grain”

What is a Grain?

A grain is the level of detail at which a business measurement is stored

Different businesses have different fact needs

A Social Services grain

The number of food stamp dollars given to a case each month

In-Home Support Services grain

The number of hours of service a client received in a provider’s pay period

The number of dollars paid to a provider for a client during a pay period

What is a Dimension ?

A dimension is a textual description that relates to a fact, for example:

Ethnicity (White, Black, Japanese)

Language (English, Spanish, Tagalog)

Gender (Male, Female)

Date (05/31/2003, 04/15/2003)

Location (California, Arizona, New Mexico)

Used in Queries

Dimensions are used to restrict and frame queries on facts, for example:

“ Give me a count of all Spanish speaking white males in California”

The fact is the count (a number)

The dimensions are:

Spanish (language),

white (race),

male (gender),

and California (location)

Identifying Facts and Dimensions The Facts are “math” words The Dimensions are “grouping” words

What makes a Data Warehouse ?

Reporting Cubes In this report, The fact is: (count of) Unique Client The dimensions are: (by) Department (by) Gender (by) Active Year Reporting cubes provide a powerful and flexible way to look at data to answer business questions

Reporting Cubes Again the fact is (count of) Clients The dimensions are (by) Race Group (by) Department (for) Active Year

Drill Down Capable Cubes can provide for drilling down into greater levels of detail. From the previous report we have “drilled” into the Social Services Division, “down” to the program level.

Multi -Dimensional This report shows that we can combine dimensions to find even more interesting information.

Visual Graphs Depending on the reporting tool, these reports can easily be converted in to graphs allowing the user to quickly visualize the information.

Cubes Answer Business Questions

How many Spanish speaking clients did H&HS serve in each department for each of the past 3 years?

Which cities currently have the highest concentration of Asian clients? What has the trend been?

How many people who receive Medi-Cal received a service in 2003 from health services, by service?

Where do we start ?

Choose the systems to include

Identify the exact grain of the business process

Identify the dimensions available for use with each fact table row

Choose the numeric facts of what is being measured

Key to Success

To ensure success end user involvement is required:

Data warehouse success is tied directly to user acceptance. If the users haven’t accepted the data warehouse …then your efforts have been exercises in futility. (Kimball, 2002)