A distributed relational database consists of a set of SQL objects that are spread across interconnected computer systems.
These relational databases can be of the same type (for example, DB2® UDB for iSeries™) or of different types (DB2 Universal Database™ for z/OS®, DB2 for VSE and VM, DB2 Universal Database™ (UDB), or non-IBM database management systems which support DRDA®). Each relational database has a relational database manager to manage the tables in its environment. The database managers communicate and cooperate with each other in a way that allows a given database manager access to run SQL statements on a relational database on another system.
The application requester supports the application side of a connection. The application server is the local or remote database to which an application requester is connected. DB2 UDB for iSeries provides support for Distributed Relational Database Architecture™ (DRDA) to allow an application requester to communicate with application servers. In addition, DB2 UDB for iSeries can call exit programs to allow access to data on other database management systems which do not support DRDA. These exit programs are called application requester driver (ARD) programs.
DB2 UDB for iSeries supports two levels of distributed relational database:
Remote unit of work is where the preparation and running of SQL statements occurs at only one application server during a unit of work. DB2 UDB for iSeries supports RUW over either APPC or TCP/IP.
Distributed unit of work is where the preparation and running of SQL statements can occur at multiple applications servers during a unit of work. However, a single SQL statement can only refer to objects located at a single application server. DB2 UDB for iSeries supports DUW over APPC and, beginning in V5R1, introduced support for DUW over TCP/IP.