1. Data Mining
Data Warehouses

2. Data Warehousing and OLAP Technology: An Overview
What is a data warehouse?
A multi-dimensional data model
Data warehouse architecture
From data warehousing to data mining

3. What is Data Warehouse?
Defined in many different ways, but not rigorously.
A decision support database that is maintained separately from the organization’s operational database
Support information processing by providing a solid platform of consolidated, historical data for analysis.
“A data warehouse is a subject-oriented, integrated, time- variant, and nonvolatile collection of data in support of management’s decision-making process.”—W. H. Inmon
Data warehousing:
The process of constructing and using data warehouses

4. Data Warehouse—Subject-Oriented
Organized around major subjects, such as customer, product, sales
Focusing on the modeling and analysis of data for decision makers, not on daily operations or transaction processing
Provide a simple and concise view around particular subject issues by excluding data that are not useful in the decision support process

5. Data Warehouse—Integrated
Constructed by integrating multiple, heterogeneous data sources
relational databases, flat files, on-line transaction records
Data cleaning and data integration techniques are applied.
Ensure consistency in naming conventions, encoding structures, attribute measures, etc. among different data sources
E.g., Hotel price: currency, tax, breakfast covered, etc.
When data is moved to the warehouse, it is converted.

6. Data Warehouse—Time Variant
The time horizon for the data warehouse is significantly longer than that of operational systems
Operational database: current value data
Data warehouse data: provide information from a historical perspective (e.g., past 5-10 years)
Every key structure in the data warehouse
Contains an element of time, explicitly or implicitly
But the key of operational data may or may not contain “time element”

7. Data Warehouse—Nonvolatile
A physically separate store of data transformed from the operational environment
Operational update of data does not occur in the data warehouse environment
Does not require transaction processing, recovery, and concurrency control mechanisms
Requires only two operations in data accessing:
initial loading of data and access of data

8. Data Warehouse vs. Operational DBMS
OLTP (on-line transaction processing)
Major task of traditional relational DBMS
Day-to-day operations: purchasing, inventory, banking, manufacturing, payroll, registration, accounting, etc.
OLAP (on-line analytical processing)
Major task of data warehouse system
Data analysis and decision making
Distinct features (OLTP vs. OLAP):
User and system orientation: customer vs. market
Data contents: current, detailed vs. historical, consolidated
Database design: ER + application vs. star + subject
View: current, local vs. evolutionary, integrated
Access patterns: update vs. read-only but complex queries

9. OLTP vs. OLAP

10. Data Warehousing and OLAP Technology: An Overview
What is a data warehouse?
A multi-dimensional data model
Data warehouse architecture
From data warehousing to data mining

11. From Tables and Spreadsheets to Data Cubes
A data warehouse is based on a multidimensional data model which views data in the form of a data cube
A data cube, such as sales, allows data to be modeled and viewed in multiple dimensions
Dimension tables, such as item (item_name, brand, type), or time(day, week, month, quarter, year)
Fact table contains measures (such as dollars_sold) and keys to each of the related dimension tables

12. Conceptual Modeling of Data Warehouses
Modeling data warehouses: dimensions & measures
Star schema: A fact table in the middle connected to a set of dimension tables
Snowflake schema: A refinement of star schema where some dimensional hierarchy is normalized into a set of smaller dimension tables, forming a shape similar to snowflake

13. Example of Star Schema item branch time Sales Fact Table time_key
day
day_of_the_week
month
quarter
year
time
item_key
item_name
brand
type
supplier_type
item
Sales Fact Table
time_key
item_key
branch_key
branch_key
branch_name
branch_type
branch
location_key
street
city
state_or_province
country
location
location_key
units_sold
dollars_sold
avg_sales
Measures

14. Example of Star Schema

15. Example of Snowflake Schema
time_key
day
day_of_the_week
month
quarter
year
time
item_key
item_name
brand
type
supplier_key
item
supplier_key
supplier_type
supplier
Sales Fact Table
time_key
item_key
branch_key
location_key
street
city_key
location
branch_key
branch_name
branch_type
branch
location_key
units_sold
city_key
city
state_or_province
country
dollars_sold
avg_sales
Measures

16. Example of Snowflake Schema

17. Data Cubes Allows data to be modeled and viewed in multiple dimensions
Another representation like star schema
Dimensions are entities which you want to keep records
Time, item, branch, location…
Each dimension has a table called dimension table

18. 3-D Data Cube 4-D cubes can be visualized as a series of 3-D cubes
Supplier 1
Supplier 2
Supplier 3

19. Cuboid A data cube is often referred as a cuboid
Can generate a cubiod for all possible subsets of dimensions
Provide different level of summarization
N-D cube  base cuboid
Lowest level of summary
0-D cube  apex cuboid
Highest level of summary
Summary over all dimensions

20. Cube: A Lattice of Cuboids
all
time
item
location
supplier
time,location
time,supplier
item,location
item,supplier
location,supplier
time,item,supplier
time,location,supplier
item,location,supplier
0-D(apex) cuboid
1-D cuboids
2-D cuboids
3-D cuboids
4-D(base) cuboid
time,item
time,item,location
time, item, location, supplier

21. Ex. Data Cube Gen
Start with time-product (2-D) table that shows sale amounts TV PC
VCR
1st Qtr
1000
850
350
2nd Qtr
1352
940
298
3rd Qtr
1450
658
314
4th Qtr
1500
965
365
USA

22. Ex. Data Cube Gen (3D) USA Canada Mexico TV PC VCR 1st Q 1000 850 350
2600
750
425
1300
2nd Q
1352
940
298
1752
860
236
1200
400
3rd Q
1450
658
314
1055
458
520
1150
555
510
4th Q
1500
965
365
1350
1065
390
900
USA
Canada
Mexico

23. A Sample Data Cube All, All, All Date Product Country
Total annual sales
of TV in U.S.A.
Date
Product
Country
All, All, All
sum TV
VCR PC
1Qtr
2Qtr
3Qtr
4Qtr
U.S.A
Canada
Mexico

24. Cuboids Corresponding to the Cube
all
0-D(apex) cuboid
country
product
date
1-D cuboids
product,date
product,country
date, country
2-D cuboids
3-D(base) cuboid
product, date, country

25. Multidimensional Data
Sales volume as a function of product, month, and region
Dimensions: Product, Location, Time
Hierarchical summarization paths
Region
Industry Region Year
Category Country Quarter
Product City Month Week
Office Day
Product
Month

26. A Concept Hierarchy: Dimension (location)
all
all
Europe
...
North_America
region
Germany
...
Spain
Canada
...
Mexico
country
Vancouver
...
city
Frankfurt
...
Toronto
L. Chan
...
M. Wind
office

27. Typical OLAP Operations
Roll up (drill-up): summarize data
by climbing up hierarchy or by dimension reduction
Drill down (roll down): reverse of roll-up
from higher level summary to lower level summary or detailed data, or introducing new dimensions
Slice and dice:
project and select
Pivot (rotate):
reorient the cube, visualization, 3D to series of 2D planes

29. Chapter 3: Data Warehousing and OLAP Technology: An Overview
What is a data warehouse?
A multi-dimensional data model
Data warehouse architecture
From data warehousing to data mining

30. Data Warehouse: A Multi-Tiered Architecture
Operational
DBs
Other
sources
Monitor
&
Integrator
OLAP Server
Metadata
Extract
Transform
Load
Refresh
Analysis
Query
Reports
Data mining
Serve
Data
Warehouse
Data Marts
Data Sources
Data Storage
OLAP Engine
Front-End Tools

31. Warehouse Architecture
Data Mart
a subset of corporate-wide data that is of value to a specific groups of users. Its scope is confined to specific, selected groups, such as marketing data mart
Meta data is the data defining warehouse objects. It stores:
Description of the structure of the data warehouse
schema, view, dimensions, hierarchies, data mart locations and contents
Monitoring information
warehouse usage statistics, error reports
Algorithms used for summarization

32. Chapter 3: Data Warehousing and OLAP Technology: An Overview
What is a data warehouse?
A multi-dimensional data model
Data warehouse architecture
From data warehousing to data mining

33. Data Warehouse Usage Three kinds of data warehouse applications
Information processing
supports querying, basic statistical analysis, and reporting using crosstabs, tables, charts and graphs
Analytical processing
multidimensional analysis of data warehouse data
supports basic OLAP operations, slice-dice, drilling, pivoting
Data mining
knowledge discovery from hidden patterns
supports associations, constructing analytical models, performing classification and prediction, and presenting the mining results using visualization tools

34. Chapter 3: Data Warehousing and OLAP Technology: An Overview
What is a data warehouse?
A multi-dimensional data model
Data warehouse architecture
From data warehousing to data mining
Summary

35. Summary: Data Warehouse and OLAP Technology
Why data warehousing?
A multi-dimensional model of a data warehouse
Star schema, snowflake schema
A data cube consists of dimensions & measures
OLAP operations: drilling, rolling, slicing, dicing and pivoting
Data warehouse architecture