How client applications interact with data sources

To client applications, the data sources in a federated system appear as a single collective database. To obtain data from data sources, applications submit queries in SQL to the federated database. The federated database then distributes the queries to the appropriate data sources, and either returns this data to the applications or performs the requested action.

The federated database can join data from local tables and remote data sources in the same SQL statement. For example, you can join data that is located in a local Db2® table, an Informix® table, and a Sybase view in a single SQL statement. By processing SQL statements as if the data sources were ordinary relational tables or views within the federated database, the federated system can join relational data and nonrelational data.

In a federated system, you can access data sources through nicknames. A nickname is a federated database object that an application uses to reference a data source object, such as a table or view. To write to a data source—for example, to update a data source table—an application can use Db2 SQL (with nicknames). Alternatively, applications can use the SQL dialect of the data source (without nicknames) in a special session called pass-through to access the data sources directly.

Applications that use SQL and nicknames can access any data types that the federated database recognizes.

The federated database catalog contains information about the objects in the federated database and information about objects at the data sources. Because the catalog contains information about the entire federated database, it is called a global catalog.