PATTERNS OF DATA MODELING- P28: Models provide the means for building quality software in a predictable manner. Models let developers think deeply about software and cope with large size and complexity. Developers can think abstractly before becoming enmeshed in the details of writing code. Although models are beneficial, they can be difficult to construct. That is where patterns come in. Patterns provide building blocks that help developers construct models faster and better. | 118 Chapter 9 Non-Data-Warehouse Antipatterns into a single dimension entity. For example Figure collapses the Product dimension of Figure into a single entity. Product 1 Category 1 Industry productName productNumber categoryName industryName I Product productName productNumber categoryName industryName a Snowflaked dimension b Collapsed dimension Figure Combined entity types Collapsing a snowflaked dimension. It is acceptable to combine entity types for a dimension of a data warehouse. Chapter Summary An antipattern is a characterization of a common software flaw. The antipatterns in Table simplify reading but compromise the ability of database structure to enforce quality. These antipatterns are often acceptable for data warehouses but you should avoid them otherwise. Table Summary of Non-Data-Warehouse Antipatterns Antipattern name Observation Exceptions Resolution Frequency Derived data A model has elements that are not fundamental. OK for critical elements bottlenecks and data warehouses. Rework the model to eliminate derived data. Common Parallel attributes An entity type has groups of similar attributes. Often used for data warehouses. Abstract and factor out commonality. Occasional Parallel relationships Two entity types have several similar relationships. Can be acceptable for a data warehouse. Abstract and factor out commonality. Occasional Combined entity types An entity type has disparate attributes. OK for I O staging and data warehouses. Make each concept its own entity type. Occasional Part III Archetypes Chapter 10 Archetypes 121 Archetypes are deep abstractions that often occur and transcend individual applications. You should keep them in mind as you construct models. This chapter presents both UML and IDEF1X diagrams so that the meaning of the archetypes is clear for readers who prefer one or the other notation. 119 10 Archetypes Archetypes are abstractions that often occur and transcend individual applications. You .
