Decision Support Systems 1201311 Data Warehousing Chattrakul Sombattheera

Agenda • • Definitions and Concepts Process Overview Architecture Data Integration and the ETL Processes Development Real-Time Data Warehousing Administration and Security Issues

Definitions and Concepts • A data warehouse (DW) is a pool of data produced to support decision making; it is also a repository of current and historical data of potential interest to managers throughout the organization. • Data are usually structured to be available in form ready for analytical processing activities (e. g. , online analytical processing [OLAP], data mining, querying, reporting, other decision support applications). • A data warehouse is a subject-oriented, integrated, timevariant, nonvolatile collection of data in support of management’s decision-making process.

Characteristics of DW • Subject-oriented. Data are organized by detailed subject, such as sales, products, or customers, containing only information relevant for decision support that allows decision makers to both know how their business performs and why. – A DW differs from typical DBs that they are more product-oriented and are tuned to handle transactions of DBs. Subject orientation allows a more comprehensive view of organization • Integrated. Data are from different sources and must be in a consistent form. DWs must deal with naming conflicts and discrepancies among units of measure. • Time variant (time series). A DW usually contains historical data (containing multiple time points, e. g. daily, weekly, monthly), except in real-time systems. They detect trends, deviations, long-term relationships forecasting and comparisons, leading to decision making. • Nonvolatile. Users cannot change data in DWs. Obsolete data are discarded, and changes are recorded as new data.

Additional DW Characteristics • Web-based. DWs are typically web-based application. • Relational/Multidimensional. DWs use either a relational structure or multidimensional structure. • Client/server. DWs use client/server architecture to provide easy access to end users. • Real-time. Newer DWs provide real-time or active, data access and analysis capabilities. • Include metadata. DWs contain metadata (data about data) about how data organized and how to effectively use them.

Parts of DWs. • Data Marts. A data mart is a subset of a DW, typically consisting of a single subject area (e. g. marketing, operations). • Operational Data Stores (ODS). An ODS provides a fairly recent form of customer information file (CIF) and is used for short-term decision involving mission-critical applications. The contents of an ODS are updated through the course of business operations. • Enterprise Data Warehouses (EDW). An EDW is a large scale DW that is used across the enterprise for decision support. EDW are used to provide data for many types of DSS, including customer relation management (CRM), supply chain management (SCM), business performance management (BPM), business activity monitoring (BAM), product lifecycle management (PLM), revenue management, knowledge management systems (KMS), etc.

DW Process Overview • • • Data sources. Data come from various sources including legacy systems, external data providers, online transaction processing (OLTP), enterprise resource planning (ERP) system, Web logs, etc. Data extractions. Data are extracted using custom-written or commercial software (ETL). Data loading. Data are loaded into staging area, where they are transformed and cleansed. Comprehensive database. EDWs support all decision analysis by providing relevant summarised and detailed information originating from many different sources. Metadata. Medata are maintained so that they can be accessed by IT personnel and users. Metadata include software programs about data and rules for organizing data summaries that are easy to index and search. Middleware tools enable access to the data warehouse. Middleware tools include SQL, Business Object, applications (data mining, OLAP, reporting tools, data visualize tools), etc.

DW Process Overview

DW Architectures

DW Architecture

DW Architectures

10 Factors for choosing DW architecture • Information interdependence between organizational units • Upper management’s information needs • Urgency of need for a data warehouse • Nature of end-user tasks • Constraints on resources • Strategic view of the data warehouse prior to implementation • Compatibility with existing systems • Perceived ability of the in-house IT staff • Technical issues • Social/Political factors

Data Integration • Data integration comprises three major processes that, when correctly implemented, permit data to be accessed and made accessible to an array of ETL and analysis tools and data warehousing environment: – Data access (i. e. , the ability to access and extract data from any data source), – Data federation (i. e. , the integration of business views across multiple data stores), and – Change capture (i. e. , based on the indentification, cpature, and delivery of the changes made to enterprise data sources).

Data Integration Techniques • Enterprise application integration (EAI) provides a vehicle for pushing data from source systems into the data warehouse. • EAI involves integrating application functionality and is focused on sharing functionality (rather than data) across systems, thereby enabling flexibility and reuse. • Traditional EAP focuses on enabling application reuse at the programming level, whereas modern EAP uses services-oriented architecture (SOA). • Enterprise information integration (EII) proposes real-time data integration from a variety of sources, such as relational databases, Web services, and multidimensional databases. • EII tools use predefined metadata to populate views that make integrated data appear relational to end users. XML seems to be the most appropriate tool to define metadata.

Extraction, Transformation, and Load (ETL) • • ETL is the heart of DW. ETL is composed of – Extraction: reading data from one or more databases, – Transformation: converting the extracted data from its previous form into the form in which it needs to be so that it can be placed into a data warehouse or simply another database, and – Load: putting the data into datawarehouse. • • • Transformation occurs by using rules or lookup tables or by combining the data with other data. The three database functions are integrated into one tool to pull data out of one or more databases and place them into another, consolidated database or a data warehouse. ETL tools transport data between sources and targets, document how data elements (e. g. metadata) change as the move between source and target, exchange metadata with other application as needed, and administer all runtime processes and operations (e. g. , scheduling, error management, audit logs, statistics).

ETL Process

DW Development Approaches • The inmon Model: The EDW Approach • The Kimbell Model: The Data Mart Approach

DW Structure: Star Schema