Figure 8.4: SQL with the RDA protocol.
A user may run an application on a client workstation which sends SQL statements to a remote system by means of the RDA protocol. The remote system (called a SQL server) returns the results of the SQL statements to the client workstation. As illustrated in figure 8.4, the application on the RDA client is a X and RDA client application which drives the RDA client's keyboard and screen by means of the X server executing on the RDA client workstation. The protocol, which specifies how SQL statements are communicated to the SQL server and how the SQL server returns results, shown in figure 8.4 is RDA.
RDA is specified in ISO 9579. RDA is an application layer protocol in an OSI stack. The RDA standard is in two parts: Generic RDA and SQL specialization. Generic RDA specifies a protocol which can support database operations but does not specify the syntax or semantics of the database operations sent from client to server. The SQL Specialization defines how SQL is to be used in conjunction with Generic RDA.
RDA fits within an OSI stack in one of two ways. In the Basic Application Context, RDA is supported by ACSE and is based on a simple client/server model. This model only describes how a single SQL client interacts with a single SQL server. The Basic Application Context does not support distributed database applications. In order to support distributed database applications, the Transaction Processing (TP) Application Context must be used. In the TP Application Context, RDA is supported by ISO TP (ISO 10026-3) and ISO CCR (ISO 9805).