ETL The process of updating the data warehouse. Recent Developments in Data Warehousing: A Tutorial Hugh J. Watson Terry College of Business University of Georgia [email protected] http://www.terry.uga.edu/~hwatson/dw_tutorial.ppt
Two Data Warehousing Strategies Enterprise-wide warehouse, top down, the Inmon methodology Data mart, bottom up, the Kimball methodology When properly executed, both result in an enterprise-wide data warehouse
The Data Mart Strategy The most common approach Begins with a single mart and architected marts are added over time for more subject areas Relatively inexpensive and easy to implement Can be used as a proof of concept for data warehousing Can perpetuate the silos of information problem Can postpone difficult decisions and activities Requires an overall integration plan
The Enterprise-wide Strategy A comprehensive warehouse is built initially An initial dependent data mart is built using a subset of the data in the warehouse Additional data marts are built using subsets of the data in the warehouse Like all complex projects, it is expensive, time consuming, and prone to failure When successful, it results in an integrated, scalable warehouse
Data Sources and Types Primarily from legacy, operational systems Almost exclusively numerical data at the present time External data may be included, often purchased from third-party sources Technology exists for storing unstructured data and expect this to become more important over time
Extraction, Transformation, and Loading (ETL) Processes The plumbing work of data warehousing Data are moved from source to target data bases A very costly, time consuming part of data warehousing Recent Development: More Frequent Updates
Updates can be done in bulk and trickle modes Business requirements, such as trading partner access to a Web site, requires current data For international firms, there is no good time to load the warehouse Recent Development: Clickstream Data Results from clicks at web sites
A dialog manager handles user interactions. An ODS (operational data store in the data staging area) helps to custom tailor the dialog The clickstream data is filtered and parsed and sent to a data warehouse where it is analyzed Software is available to analyze the clickstream data Data Extraction
Often performed by COBOL routines (not recommended because of high program maintenance and no automatically generated meta data) Sometimes source data is copied to the target database using the replication capabilities of standard RDMS (not recommended because of dirty data in the source systems) Increasing performed by specialized ETL software
Sample ETL Tools Teradata Warehouse Builder from Teradata DataStage from Ascential Software SAS System from SAS Institute Power Mart/Power Center from Informatica Sagent Solution from Sagent Software Hummingbird Genio Suite from Hummingbird Communications
Reasons for Dirty Data
Dummy Values Absence of Data Multipurpose Fields Cryptic Data Contradicting Data Inappropriate Use of Address Lines Violation of Business Rules Reused Primary Keys, Non-Unique Identifiers Data Integration Problems
Data Cleansing Source systems contain dirty data that must be cleansed ETL software contains rudimentary data cleansing capabilities Specialized data cleansing software is often used. Important for performing name and address correction and householding functions Leading data cleansing vendors include Vality
(Integrity), Harte-Hanks (Trillium), and Firstlogic (i.d.Centric) Steps in Data Cleansing Parsing Correcting Standardizing Matching Consolidating Parsing
Parsing locates and identifies individual data elements in the source files and then isolates these data elements in the target files. Examples include parsing the first, middle, and last name; street number and street name; and city and state. Correcting Corrects parsed individual data
components using sophisticated data algorithms and secondary data sources. Example include replacing a vanity address and adding a zip code. Standardizing Standardizing applies conversion routines to transform data into its preferred (and consistent) format using both standard and custom
business rules. Examples include adding a pre name, replacing a nickname, and using a preferred street name. Matching Searching and matching records within and across the parsed, corrected and standardized data based on predefined business rules to eliminate duplications.
Examples include identifying similar names and addresses. Consolidating Analyzing and identifying relationships between matched records and consolidating/merging them into ONE representation. Data Staging Often used as an interim step between data
extraction and later steps Accumulates data from asynchronous sources using native interfaces, flat files, FTP sessions, or other processes At a predefined cutoff time, data in the staging file is transformed and loaded to the warehouse There is usually no end user access to the staging file An operational data store may be used for data staging
Data Transformation Transforms the data in accordance with the business rules and standards that have been established Example include: format changes, deduplication, splitting up fields, replacement of codes, derived values, and aggregates Data Loading
Data are physically moved to the data warehouse The loading takes place within a load window The trend is to near real time updates of the data warehouse as the warehouse is increasingly used for operational applications Meta Data Data about data
Needed by both information technology personnel and users IT personnel need to know data sources and targets; database, table and column names; refresh schedules; data usage measures; etc. Users need to know entity/attribute definitions; reports/query tools available; report distribution information; help desk contact information, etc. Recent Development:
Meta Data Integration A growing realization that meta data is critical to data warehousing success Progress is being made on getting vendors to agree on standards and to incorporate the sharing of meta data among their tools Vendors like Microsoft, Computer Associates, and Oracle have entered the meta data marketplace with significant product offerings
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