25. Data Warehouses and Decision Support
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Transcript of 25. Data Warehouses and Decision Support
04/19/23 1PSU’s CS 587-3
25. Data Warehouses and Decision Support
Len Shapiro, for CS386, 11/2-3/05.Some slides taken from Ramakrishnan
and Gherke, with permission.
04/19/23 2PSU’s CS 587-3
Overview
Increasingly, organizations are analyzing current and historical data to identify useful patterns and support business strategies.
Emphasis is on complex, interactive, exploratory analysis of very large datasets created by integrating data from across all parts of an enterprise; data is fairly static. Contrast such On-Line Analytic Processing
(OLAP) with traditional On-line Transaction Processing (OLTP): mostly long queries, instead of short update Xacts.
25. Whs.
04/19/23 3PSU’s CS 587-3
Enterprise Applications
OLTP / Operational / Production
DSS / Warehouse / DataMart
Operate the business / Clerks Diagnose the business / Managers
Short queries, small amts of data
opposite
Queries change data opposite
Customer inquiry, Order Entry, etc.
Statistics, Visualization, Data Mining, etc.
Legacy Applications, Heterogeneous databases
Opposite
Often Distributed Often Centralized (Warehouse)
Current data Current and Historical data
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04/19/23 4PSU’s CS 587-3
Data Warehouse Requirements
Operational Warehouse
General E-R Diagrams Multidimensional data model common
Locks necessary No Locks necessary
Crash recovery required Crash recovery optional
Smaller volume of data Huge volume of data
Need indexes designed to access small amounts of data
Need indexes designed to access large volumes of data
04/19/23 5PSU’s CS 587-3
Data Warehousing
Integrated data spanning long time periods, often augmented with summary information.
Several gigabytes to terabytes common.
Interactive response times expected for complex queries; ad-hoc updates uncommon.
EXTERNAL DATA SOURCES
EXTRACTTRANSFORM LOAD REFRESH
DATAWAREHOUSE Metadata
Repository
SUPPORTS
OLAPDATAMINING
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04/19/23 6PSU’s CS 587-3
25.2 Multidimensional Data Model
Collection of numeric measures, which depend on a set of dimensions. E.g., measure Sales, dimensions
Product (key: pid), Location (locid), and Time (timeid).
8 10 10
30 20 50
25 8 15
1 2 3 timeid
p
id11
12
13
11 1 1 25
11 2 1 8
11 3 1 15
12 1 1 30
12 2 1 20
12 3 1 50
13 1 1 8
13 2 1 10
13 3 1 10
11 1 2 35
pid
tim
eid
locid
sale
s
locid
Slice locid=1is shown:
04/19/23 7PSU’s CS 587-3
Examples of Dimensional Data
Products(ProductID, StoreID, DateID, Sale) Product(ID, SKU, size, brand) Store(ID, Address, Sales District, Region, Manager) Date (Date, Week, Month, Holiday, Promotion)
Claims(ProvID, MembID, Procedure, DateID, Cost) Providers(ID, Practice, Address, ZIP, City, State) Members(ID, Contract, Name, Address) Procedure (ID, Name, Type)
Telecomm (CustID, SalesRepID, ServiceID, DateID) SalesRep(ID, Address, Sales District, Region, Manager) Service(ID, Name, Category)
04/19/23 8PSU’s CS 587-3
MOLAP vs ROLAP
Multidimensional data can be stored physically in a (disk-resident, persistent) array; called MOLAP systems. Alternatively, can store as a relation; called ROLAP systems.
The main relation, which relates dimensions to a measure, is called the fact table. Each dimension can have additional attributes and an associated dimension table. E.g., Products(pid, pname, category, price) Fact tables are much larger than dimensional tables.
25. Whs.
04/19/23 9PSU’s CS 587-3
Dimension Hierarchies
For each dimension, some of the attributes may be organized in a hierarchy:
PRODUCT TIME LOCATION
pname week city
PID date ZIP
year
category quarter state
25. Whs.
04/19/23 10PSU’s CS 587-3
25.3 OLAP Queries
Influenced by SQL and by spreadsheets. A common operation is to aggregate a
measure over one or more dimensions. Find total sales. Find total sales for each city, or for each state. Find top five products ranked by total sales.
Roll-up: Aggregating at different levels of a dimension hierarchy. E.g., Given total sales by city, we can roll-up to
get sales by state.
25. Whs.
04/19/23 11PSU’s CS 587-3
OLAP Queries Drill-down: The inverse of roll-up.
E.g., Given total sales by state, can drill-down to get total sales by city.
E.g., Can also drill-down on different dimension to get total sales by product for each state.
Pivoting: Aggregation on selected dimensions. E.g., Pivoting on Location and Time
yields this cross-tabulation:63 81 144
38 107 145
75 35 110
WI CA Total
2002
2003
2004
176 223 339Total
Slicing and Dicing: Equality and range selections on one or more dimensions.
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04/19/23 12PSU’s CS 587-3
Comparison with SQL Queries The cross-tabulation obtained by pivoting can also be
computed using a collection of SQLqueries:
SELECT SUM(S.sales)FROM Sales S, Times T, Locations LWHERE S.timeid=T.timeid AND S.timeid=L.timeidGROUP BY T.year, L.state
SELECT SUM(S.sales)FROM Sales S, Times TWHERE S.timeid=T.timeidGROUP BY T.year
SELECT SUM(S.sales)FROM Sales S, Location LWHERE S.timeid=L.timeidGROUP BY L.state
25. Whs.
04/19/23 13PSU’s CS 587-3
The CUBE Operator
Generalizing the previous example, if there are k dimensions, we have 2^k possible SQL GROUP BY queries that can be generated through pivoting on a subset of dimensions.
CUBE pid, locid, timeid BY SUM Sales Equivalent to rolling up Sales on all eight subsets
of the set {pid, locid, timeid}; each roll-up corresponds to an SQL query of the form:
SELECT SUM(S.sales)FROM Sales SGROUP BY grouping-list
Lots of work on optimizing the CUBE operator!
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04/19/23 14PSU’s CS 587-3
Summary Decision support is an emerging, rapidly growing
subarea of databases. Involves the creation of large, consolidated data
repositories called data warehouses. Warehouses exploited using sophisticated analysis
techniques: complex SQL queries and OLAP “multidimensional” queries (influenced by both SQL and spreadsheets).
New techniques for database design, indexing, view maintenance, and interactive querying need to be supported (CS587).
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