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Chapter 13
The Data Warehouse
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The Need for Data Analysis
• Managers must be able to track daily
transactions to evaluate how the business is
performing
• By tapping into the operational database,
management can develop strategies to meet
organizational goals
• Data analysis can provide information about
short-term tactical evaluations and strategies
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Solving Business Problems and Adding
Value with Data Warehouse-Based Solutions
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Solving Business Problems and Adding Value
with Data Warehouse-Based Solutions (continued)
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Decision Support Systems
• Methodology (or series of methodologies)
designed to extract information from data and to
use such information as a basis for decision
making
• Decision support system (DSS):
– Arrangement of computerized tools used to assist
managerial decision making within a business
– Usually requires extensive data “massaging” to
produce information
– Used at all levels within an organization
– Often tailored to focus on specific business areas
– Provides ad hoc query tools to retrieve data and
to display data in different formats
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Decision Support Systems (continued)
• Composed of four main components:
– Data store component
• Basically a DSS database
– Data extraction and filtering component
• Used to extract and validate data taken from
operational database and external data sources
– End-user query tool
• Used to create queries that access database
– End-user presentation tool
• Used to organize and present data
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Main Components of a
Decision Support System (DSS)
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Transforming Operational Data Into
Decision Support Data
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Contrasting Operational and DSS Data
Characteristics
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The Data Warehouse
• Integrated, subject-oriented, time-variant,
nonvolatile database that provides support for
decision making
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A Comparison of Data Warehouse and
Operational Database Characteristics
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Creating a Data Warehouse
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The ETL Process
•
•
•
•
Capture/Extract
Scrub or data cleansing
Transform
Load and Index
ETL = Extract, transform, and load
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Capture/Extract…obtaining a snapshot of a chosen subset
of the source data for loading into the data warehouse
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Figure 11-10:
Steps in data
reconciliation
Static extract = capturing
a snapshot of the source
data at a point in time
Incremental extract =
capturing changes that
have occurred since the last
static extract
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Scrub/Cleanse…uses pattern recognition and AI
techniques to upgrade data quality
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Figure 11-10:
Steps in data
reconciliation
(cont.)
Fixing errors: misspellings,
erroneous dates, incorrect field
usage, mismatched addresses,
missing data, duplicate data,
inconsistencies
Also: decoding, reformatting,
time stamping, conversion, key
generation, merging, error
detection/logging, locating
missing data
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Cleanse:
• Process to identify erroneous data, not to fix
them
• Fixes are made at the source
Scrubbing:
A technique using pattern recognition and other
AI techniques to upgrade the quality of data
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Transform = convert data from format of operational
system to format of data warehouse
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Figure 11-10:
Steps in data
reconciliation
(cont.)
Record-level:
Selection–data partitioning
Joining–data combining
Aggregation–data summarization
Field-level:
single-field–from one field to one field
multi-field–from many fields to one, or
one field to many
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Load/Index= place transformed data
into the warehouse and create indexes
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Figure 11-10:
Steps in data
reconciliation
(cont.)
Refresh mode: bulk rewriting
of target data at periodic intervals
Update mode: only changes
in source data are written to data
warehouse
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Figure 11-11: Single-field transformation
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In general–some transformation
function translates data from old
form to new form
Algorithmic transformation uses
a formula or logical expression
Table lookup–another
approach, uses a separate
table keyed by source
record code
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Figure 11-12: Multifield transformation
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M:1–from many source
fields to one target field
1:M–from one
source field to
many target fields
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Derived Data
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• Objectives
–
–
–
–
–
Ease of use for decision support applications
Fast response to predefined user queries
Customized data for particular target audiences
Ad-hoc query support
Data mining capabilities
• Characteristics
– Detailed (mostly periodic) data
– Aggregate (for summary)
– Distributed (to departmental servers)
Most common data model = star schema
(also called “dimensional model”)
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Star Schemas
• Data modeling technique used to map
multidimensional decision support data into a
relational database
• Creates the near equivalent of a
multidimensional database schema from the
existing relational database
• Yield an easily implemented model for
multidimensional data analysis, while still
preserving the relational structures on which
the operational database is built
• Has four components: facts, dimensions,
attributes, and attribute hierarchies
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Figure 11-13 Components of a star schema
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Fact tables contain factual
or quantitative data
1:N relationship between
dimension tables and fact tables
Dimension tables are denormalized to
maximize performance
Dimension tables contain descriptions
about the subjects of the business
Excellent for ad-hoc queries, but bad for online transaction processing
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Figure 11-14 Star schema example
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Fact table provides statistics for sales
broken down by product, period and
store dimensions
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Figure 11-15 Star schema with sample data
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Size of fact table
assume:
Total number of stores=1000
Total number of products=10,000
Total number of periods= 24 (two years)
Assume 50% of products record sales
Then total rows in fact table
1000stores* 5000 active products)*24 months
=120,000,000 rows
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Size of “fact” table
Assume there are 6 fields each 4 bytes long,
then total size
120,00,000* 6 fields* 4bytes/field
=2,880,000,000 (2.88 gigabytes)
If instead of monthly, you record daily data
Multiply above by 30 (30 days/per month)
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Online Analytical Processing
• Advanced data analysis environment that
supports decision making, business
modeling, and operations research
• OLAP systems share four main
characteristics:
– Use multidimensional data analysis
techniques
– Provide advanced database support
– Provide easy-to-use end-user interfaces
– Support client/server architecture
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Operational vs. Multidimensional
View of Sales
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Another example: Simple Star Schema
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Possible Attributes for Sales Dimensions
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Three-Dimensional View of Sales
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Slice and Dice View of Sales
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Location Attribute Hierarchy
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Star Schema for Sales
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Orders Star Schema
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Normalized Dimension tables
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Multiple Fact Tables
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On-Line Analytical Processing (OLAP) Tools
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• The use of a set of graphical tools that provides users
with multidimensional views of their data and allows
them to analyze the data using simple windowing
techniques
• Relational OLAP (ROLAP)
– Traditional relational representation
• Multidimensional OLAP (MOLAP)
– Cube structure
• OLAP Operations
– Cube slicing–come up with 2-D view of data
– Drill-down–going from summary to more detailed
views
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Figure 11-23 Slicing a data cube
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Figure 11-24
Example of drill-down
Starting with summary
data, users can obtain
details for particular
cells
Summary report
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Drill-down with
color added
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Implementing a Data Warehouse
• Numerous constraints:
– Available funding
– Management’s view of the role played by an
IS department and of the extent and depth of
the information requirements
– Corporate culture
• No single formula can describe perfect data
warehouse development
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Factors Common to Data Warehousing
• Data warehouse is not a static database
• Dynamic framework for decision support that
is always a work in progress
• Data warehouse data cross departmental
lines and geographical boundaries
• Must satisfy:
– Data integration and loading criteria
– Data analysis capabilities with acceptable
query performance
– End-user data analysis needs
• Apply database design procedures
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Data Mining
• Tools that:
– analyze data
– uncover problems or opportunities hidden in
data relationships,
– form computer models based on their findings,
and then
– use the models to predict business behavior
• Require minimal end-user intervention
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Extraction of Knowledge From Data
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Data-Mining Phases
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A Sample of Current Data Warehousing
and Data-Mining Vendors
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Data Mining and Visualization
•
•
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Knowledge discovery using a blend of statistical, AI, and computer
graphics techniques
Goals:
– Explain observed events or conditions
– Confirm hypotheses
– Explore data for new or unexpected relationships
•
Techniques
–
–
–
–
–
–
–
–
–
•
Statistical regression
Decision tree induction
Clustering and signal processing
Affinity
Sequence association
Case-based reasoning
Rule discovery
Neural nets
Fractals
Data visualization–representing data in graphical/multimedia formats
for analysis
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Summary
• Data analysis is used to derive and interpret
information from data
• Decision support is a methodology designed to
extract information from data and to use such
information as a basis for decision making
• Decision support system is an arrangement of
computerized tools used to assist managerial
decision making within a business
• Data warehouse is an integrated, subjectoriented, time-variant, nonvolatile database that
provides support for decision making
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Summary (continued)
• Online analytical processing is an advanced
data analysis environment that supports
decision making, business modeling, and
operations research
• Star schema is a data-modeling technique used
to map multidimensional decision support data
into a relational database
• The implementation of any company-wide
information system is subject to conflicting
organizational and behavioral factors
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Summary (continued)
• Data mining automates analysis of operational
data with the intention of finding previously
unknown data characteristics, relationships,
dependencies, and/or trends
• Data warehouse is storage location for decision
support data
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