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Note for Data Mining And Data Warehousing - DMDW By Abhishek Kumar

  • Data Mining And Data Warehousing - DMDW
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  • Biju Patnaik University of Technology BPUT - BPUT
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www.Vidyarthiplus.com Queries that would be complex in very normalized databases could be easier to build and maintain in data warehouses, decreasing the workload on transaction systems. Data warehousing is an efficient way to manage and report on data that is from a variety of sources, non uniform and scattered throughout a company. Data warehousing is an efficient way to manage demand for lots of information from lots of users. Data warehousing provides the capability to analyze large amounts of historical data for nuggets of wisdom that can provide an organization with competitive advantage. Operational and informational Data • Operational Data: Focusing on transactional function such as bank card withdrawals and deposits Detailed Updateable Reflects current data • Informational Data: Focusing on providing answers to problems posed by decision makers Summarized Non updateable DATA WAREHOUSE ARCHITECTURE AND ITS SEVEN COMPONENTS 1. Data sourcing, cleanup, transformation, and migration tools 2. Metadata repository 3. Warehouse/database technology 4. Data marts 5. Data query, reporting, analysis, and mining tools 6. Data warehouse administration and management 7. Information delivery system 1 Data warehouse database This is the central part of the data warehousing environment. This is the item number 2 in the above arch. diagram. This is implemented based on RDBMS technology. 2 Sourcing, Acquisition, Clean up, and Transformation Tools This is item number 1 in the above arch diagram. They perform conversions, summarization, key changes, structural changes and condensation. The data transformation is required so that the information can by used by decision support tools. The transformation produces programs, control statements, JCL code, COBOL code, UNIX scripts, and SQL DDL code etc., to move the data into data warehouse from multiple operational systems. The functionalities of these tools are listed below: To remove unwanted data from operational db Converting to common data names and attributes Calculating summaries and derived data Establishing defaults for missing data Accommodating source data definition changes 3 Meta data It is data about data. It is used for maintaining, managing and using the data warehouse. It is classified into two: Technical Meta data: It contains information about data warehouse data used by warehouse designer, administrator to carry out development and management tasks. It includes, www.Vidyarthiplus.com

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www.Vidyarthiplus.com Info about data stores Transformation descriptions. That is mapping methods from operational db to warehouse db Warehouse Object and data structure definitions for target data The rules used to perform clean up, and data enhancement Data mapping operations Access authorization, backup history, archive history, info delivery history, data acquisition history, data access etc., Business Meta data: It contains info that gives info stored in data warehouse to users. It includes, Subject areas, and info object type including queries, reports, images, video, audio clips etc. Internet home pages Info related to info delivery system Data warehouse operational info such as ownerships, audit trails etc., 4 Access tools Its purpose is to provide info to business users for decision making. There are five categories: Data query and reporting tools Application development tools Executive info system tools (EIS) OLAP tools Data mining tools 5 Data marts Departmental subsets that focus on selected subjects. They are independent used by dedicated user group. They are used for rapid delivery of enhanced decision support functionality to end users. Data mart is used in the following situation: Extremely urgent user requirement The absence of a budget for a full scale data warehouse strategy The decentralization of business needs The attraction of easy to use tools and mind sized project Data mart presents two problems: 1. Scalability: A small data mart can grow quickly in multi dimensions. So that while designing it, the organization has to pay more attention on system scalability, consistency and manageability issues 2. Data integration 6 Data warehouse admin and management The management of data warehouse includes, Security and priority management Monitoring updates from multiple sources Data quality checks Managing and updating meta data Auditing and reporting data warehouse usage and status Purging data Replicating, sub setting and distributing data Backup and recovery Data warehouse storage management which includes capacity planning, hierarchical storage management and purging of aged data etc., www.Vidyarthiplus.com

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www.Vidyarthiplus.com 7 Information delivery system • It is used to enable the process of subscribing for data warehouse info. • Delivery to one or more destinations according to specified scheduling algorithm Building a Data warehouse: There are two reasons why organizations consider data warehousing a critical need. In other words, there are two factors that drive you to build and use data warehouse. They are: Business factors: Business users want to make decision quickly and correctly using all available data. Technological factors: To address the incompatibility of operational data stores IT infrastructure is changing rapidly. Its capacity is increasing and cost is decreasing so that building a data warehouse is easy There are several things to be considered while building a successful data warehouse Business considerations: Organizations interested in development of a data warehouse can choose one of the following two approaches: Top - Down Approach (Suggested by Bill Inmon) Bottom - Up Approach (Suggested by Ralph Kimball) Top - Down Approach In the top down approach suggested by Bill Inmon, we build a centralized repository to house corporate wide business data. This repository is called Enterprise Data Warehouse (EDW). The data in the EDW is stored in a normalized form in order to avoid redundancy. The central repository for corporate wide data helps us maintain one version of truth of the data. The data in the EDW is stored at the most detail level. The reason to build the EDW on the most detail level is to leverage 1. Flexibility to be used by multiple departments. 2. Flexibility to cater for future requirements. The disadvantages of storing data at the detail level are 1. The complexity of design increases with increasing level of detail. 2. It takes large amount of space to store data at detail level, hence increased cost. Once the EDW is implemented we start building subject area specific data marts which contain data in a de normalized form also called star schema. The data in the marts are usually summarized based on the end users analytical requirements. The reason to de normalize the data in the mart is to provide faster access to the data for the end users analytics. If we were to have queried a normalized schema for the same analytics, we would end up in a complex multiple level joins that would be much slower as compared to the one on the de normalized schema. We should implement the top-down approach when 1. The business has complete clarity on all or multiple subject areas data warehosue requirements. 2. The business is ready to invest considerable time and money. The advantage of using the Top Down approach is that we build a centralized repository to cater for one version of truth for business data. This is very important for the data to be reliable, consistent across subject areas and for reconciliation in case of data related contention between subject areas. www.Vidyarthiplus.com

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www.Vidyarthiplus.com The disadvantage of using the Top Down approach is that it requires more time and initial investment. The business has to wait for the EDW to be implemented followed by building the data marts before which they can access their reports. Bottom Up Approach The bottom up approach suggested by Ralph Kimball is an incremental approach to build a data warehouse. Here we build the data marts separately at different points of time as and when the specific subject area requirements are clear. The data marts are integrated or combined together to form a data warehouse. Separate data marts are combined through the use of conformed dimensions and conformed facts. A conformed dimension and a conformed fact is one that can be shared across data marts. A Conformed dimension has consistent dimension keys, consistent attribute names and consistent values across separate data marts. The conformed dimension means exact same thing with every fact table it is joined. A Conformed fact has the same definition of measures, same dimensions joined to it and at the same granularity across data marts. The bottom up approach helps us incrementally build the warehouse by developing and integrating data marts as and when the requirements are clear. We don’t have to wait for knowing the overall requirements of the warehouse. We should implement the bottom up approach when 1. We have initial cost and time constraints. 2. The complete warehouse requirements are not clear. We have clarity to only one data mart. The advantage of using the Bottom Up approach is that they do not require high initial costs and have a faster implementation time; hence the business can start using the marts much earlier as compared to the top-down approach. The disadvantages of using the Bottom Up approach is that it stores data in the de normalized format, hence there would be high space usage for detailed data. We have a tendency of not keeping detailed data in this approach hence losing out on advantage of having detail data .i.e. flexibility to easily cater to future requirements. Bottom up approach is more realistic but the complexity of the integration may become a serious obstacle. Design considerations To be a successful data warehouse designer must adopt a holistic approach that is considering all data warehouse components as parts of a single complex system, and take into account all possible data sources and all known usage requirements. Most successful data warehouses that meet these requirements have these common characteristics: Are based on a dimensional model Contain historical and current data Include both detailed and summarized data Consolidate disparate data from multiple sources while retaining consistency Data warehouse is difficult to build due to the following reason: Heterogeneity of data sources Use of historical data Growing nature of data base Data warehouse design approach muse be business driven, continuous and iterative engineering approach. In addition to the general considerations there are following specific points relevant to the data warehouse design: www.Vidyarthiplus.com

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