Multidimensional Modeling MIS 497

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

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

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

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

Attribute relationships One to One One to One –Each customer has only one SSN. One to Many One to Many –Each customer can have several addresses. Many to Many 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 Many to One –Several phone numbers can belong to one store, and one store only.

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. 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: Practical ways of dealing with M;N relationships: –Create a relationship table –Create a compound key »Not advisable, but sometimes necessary

Hierarchies (Dimensions) Hierarchies have the same meaning as Dimensions in MicroStrategy 7. 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. 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 Data columns (usually numeric) that can be used to perform calculations needed to answer business questions. 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 are stored in Fact Tables or Base Tables Facts can be aggregated on different levels: Facts can be aggregated on different levels: Aggregated on Region level Aggregated on Country level

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

Facts (continued) Facts are used to create metrics. 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 - 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.) 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 More on metrics in a separate presentation

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