Siebel Business Analytics Server Administration Guide > Creating and Administering the Business Model and Mapping Layer in a Repository >

Defining Logical Joins

Logical tables are related to each other. How they are related is expressed in logical joins. A key property of a logical join is cardinality. Cardinality expresses how rows in one table are related to rows in the table to which it is joined. A one-to-many cardinality means that for every row in the first logical dimension table there are 0, 1, or many rows in the second logical table. The Administration Tool considers a table to be a logical fact table if it is at the Many end of all logical joins that connect it to other logical tables.

Specifying the logical table joins is required so that the Analytics Server can have the necessary metadata to translate a logical request against the business model to SQL queries against the physical data sources. The logical join information provides the Analytics Server with the many-to-one relationships between the logical tables. This logical join information is used when the Analytics Server generates queries against the underlying databases.

The joins between the logical layer and the physical layer will be automatically created if both of the following statements are true:

• You create the logical tables by simultaneously dragging and dropping all required physical tables to the Business Model and Mapping layer.
• The logical joins are the same as the joins in the Physical layer.

However, you will probably have to create some logical joins in the Business Model and Mapping layer, because you will rarely drag and drop all physical tables simultaneously except in very simple models. In the Business Model and Mapping layer, you should create complex joins with one-to-many relationships and not key or foreign key joins.

You can create logical foreign keys and logical complex joins using either the Joins Manager or the Business Model Diagram. When you create a complex join in the Physical layer, you can specify expressions and the specific columns on which to create the join. When you create a complex join in the Business Model and Mapping layer, you cannot specify expressions or columns on which to create the join. The existence of a join in the Physical layer does not require a matching join in the Business Model and Mapping layer.

CAUTION:  It is recommended that you do not have foreign keys for logical tables. However, you can create logical foreign keys and logical complex joins using either the Joins Manager or the Business Model Diagram. A logical key for a fact table must be made up of the key columns that join to the attribute tables.

To create logical joins, perform the following tasks:

• Defining Logical Joins with the Joins Manager
• Defining Logical Joins with the Business Model Diagram