Chapter 2 Physical Data Model Basics
You can use a PDM to design the structure of a data warehouse handling business data. A data warehouse environment is made of:
Data warehouse and data mart databases store historical business data from heterogeneous systems. The data warehouse database gathers all the data manipulated in a company for example, whereas the data mart focuses on smaller entities in the company.
Data warehouse and data mart databases are populated with data proceeding from different operational sources. This data transfer is implemented via a relational to relational mapping, the operational database being the data source of the data warehouse or data mart database.
For more information on relational to relational mapping see section Mapping objects in a PDM in the Working with PDMs chapter.
The purpose of maintaining such type of database is to gather in a central area all the information that may be needed in an OLAP database where queries for business analysis and decision making are performed.
You use physical diagrams to design a data warehouse or data mart database. Since these databases usually contain very large amounts of data for storage, you do not need to design them for performance. You may assign types (fact and dimension) to the database tables to have a preview of the multidimensional structure in an OLAP database.
An OLAP database shows a multidimensional view of business data. Information in an OLAP database is organized to facilitate the queries performed by different tools. Business analysts use OLAP databases to send queries and retrieve business information from the different dimensions existing in the database.
OLAP databases are populated with data usually proceeding from a data warehouse or data mart database. This data transfer is implemented via a relational to multidimensional mapping, the data warehouse or data mart database being the data source of the OLAP database.
However, when there are no large amounts of data, it is possible to have a data transfer directly from the operational database to the OLAP engine. For clarity purpose, we will not develop the operational to OLAP transfer of information in this book.
For more information on relational to multidimensional mapping see section Mapping objects in a PDM in the Working with PDMs chapter.
You have to use multidimensional diagrams to design the different dimensions and cubes within the OLAP database.
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