Understanding object mapping

Chapter 6 Working with PDMs

Understanding object mapping

You create a mapping between PDM objects to setup a structure for data movement and transformation. Data comes from a data source and is loaded in another database.

In PowerDesigner, the data source and the destination database can be designed in physical data models.

The following schema illustrates the transfer of data between the different types of databases:

Data transfer

The above diagram shows the different paths for data transfer:

From operational to data warehouse databases
From data warehouse to OLAP databases
From Operational to OLAP databases. This path is less common. Usually operational data need to be stored in a data warehouse database before they can be used in an OLAP engine. However, when there are no large amounts of data, it is possible to skip the data warehouse step and have a data transfer directly from the operational database to the OLAP engine. For clarity purpose, we will not develop this aspect of data transfer in this section

A data source is usually a database from which data is taken and sent to another database. As mentioned above, the transfer can be from operational to data warehouse or OLAP databases, or from data warehouse to OLAP databases.

Object mapping consists in linking objects in the data source to objects in the database that needs to receive data.

For a relational to relational mapping, you can associate tables or views from the source models to tables in the destination models
For a relational to multidimensional mapping, you can associate tables or views from the source models to cubes and facts in the destination models

The mapping appears as a query defined in the destination table or cube: this query allows data selection from the data source and transfer it to the destination database. You can further define the mapping by linking table columns from the source and to table columns, fact measures, or attributes.