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Multidimensional Modeling

Multidimensional Modeling. MIS 497. What is multidimensional model?. Logical view of the enterprise Shows main entities of the enterprise business and relationships between them Not tied to a physical database and tables Not E-R diagram. Model Components. Dimensions (Hierarchies in MSTR 7)

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Multidimensional Modeling

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  1. Multidimensional Modeling MIS 497

  2. What is multidimensional model? • Logical view of the enterprise • Shows main entities of the enterprise business and relationships between them • Not tied to a physical database and tables • Not E-R diagram

  3. Model Components • Dimensions (Hierarchies in MSTR 7) • Attributes • Facts • Relationships

  4. Multidimensional Data Model Example Geography Time Products Country Year Division Region Quarter Department City Month Category Store Store Manager Day Item

  5. Attributes • Attributes are abstract items with business relevance that are created for convenient qualification or summarization of data on a report. • Attribute can also be defined as column headings on a report that are not a calculation

  6. Attribute relationships • One to One • Each customer has only one SSN. • One to Many • Each customer can have several addresses. • Many to Many • Each customer can buy many items, an item can be purchased by many customers (item means SKU, not the same physical object). • Many to One • Several phone numbers can belong to one store, and one store only.

  7. Attribute relationships • Out of all relationships, Many to Many is the trickiest one. If not modeled carefully, M;N can lead to double-counting and other unhappy consequences. • Practical ways of dealing with M;N relationships: • Create a relationship table • Create a compound key • Not advisable, but sometimes necessary

  8. Hierarchies (Dimensions) • Hierarchies have the same meaning as Dimensions in MicroStrategy 7. • Hierarchies are based on relationships between Attributes. They allow end users to define and order groups of Attributes for display and browsing purposes. Time Year Quarter Month Day

  9. Facts • Data columns (usually numeric) that can be used to perform calculations needed to answer business questions. • Facts are stored in Fact Tables or Base Tables • Facts can be aggregated on different levels: Aggregated on Region level Aggregated on Country level

  10. Facts (continued) • Same facts can be represented by different column name in the DW due to various historical and design reasons. • In the example below the same fact has two different names: SALES and DOLLAR_SALES • Facts are cross-dimensional, not limited to one dimension only. In the example above, the same fact crosses two dimensions: Geography and Time.

  11. Facts (continued) • Facts are used to create metrics. • Metrics - business measurements (i.e. Dollar Sales, Units Sold, Gross Margin and etc.) used by businesses to analyze and report their performance. • Metrics are usually a fact that has a mathematical function applied to it (sum, average, max, min and etc.) • More on metrics in a separate presentation

  12. What to read for more information: • MicroStrategy 7 Project designer guide. • Have a good look at VMALL Data Model • Identify attributes, hierarchies and facts – you’ll need them for the Workshop.

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