Difference b/w Logical join and Physical Join in OBIEE 11g

1. Relationship between the logical tables was expressed by logical joins in BMM layer.

2. Logical joins express the cardinality relationships between logical tables and are a requirement for a valid business model. 

3. Specifying the logical table joins is required so that Oracle BI Server can have the necessary metadata to translate logical requests against the business model into SQL queries against the physical data sources. Logical joins help Oracle BI Server understand the relationships between the various pieces of the business model. 

4. When a query is sent to Oracle BI Server, the server figures out how to construct physical queries by examining how the logical model is structured. 

5. Examining logical joins is an integral part of this process. 

6. 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.

Physical Joins

1. Relationship between the physical tables and columns are expressed by physical join in the physical layer.

2. A primary key and foreign key relationship defines a one-to-many relationship between two tables. 

3. A foreign key is a column or a set of columns in one table that references the primary key columns in another table. 

4. The primary key is defined as a column or set of columns where each value is unique and identifies a single row of the table. 

5. Keys and joins help Oracle BI Server determine the fact–dimension relationships between tables.

6. The Physical layer typically uses foreign key joins to define relationships, whereas the Business Model and Mapping layer uses logical joins to define relationships.