Multidimensional Modeling MIS 497 What is multidimensional model
- Slides: 12
Multidimensional Modeling MIS 497
What is multidimensional model? Logical view of the enterprise n Shows main entities of the enterprise business and relationships between them n Not tied to a physical database and tables n Not E-R diagram n
Model Components Dimensions (Hierarchies in MSTR 7) n Attributes n Facts n Relationships n
Multidimensional Data Model Example Time Geography Products Year Country Division Quarter Region Department Month City Category Day Store Manager Item
Attributes n n 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
Attribute relationships n n 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.
Attribute relationships n n 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
Hierarchies (Dimensions) n n Hierarchies have the same meaning as Dimensions in Micro. Strategy 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
Facts n n n 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
Facts (continued) n n n 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.
Facts (continued) n n 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
What to read for more information: Micro. Strategy 7 Project designer guide. n Have a good look at VMALL Data Model n – Identify attributes, hierarchies and facts – you’ll need them for the Workshop.
