ODBC Architecture

All of those AVEVA products that incorporate Query functionality have the potential to access data controlled by external systems. The Query products communicate with the data servers via the ODBC interface.

In the figure overleaf:

• Query: processes macro commands and submits Structured Query Language (SQL) commands for direct execution and retrieves results. The SQL commands are expressed in the dialect of the particular ODBC driver but with the option of using driver independent ODBC escape sequences for some values and syntax elements.

• ODBC Driver Manager: loads and unloads drivers on behalf of Query and processes ODBC requests or passes them to an ODBC driver.

• ODBC Driver: processes ODBC requests, submits SQL requests to a specific data source, and returns results to Query. If necessary, the driver modifies an application’s request so that the request conforms to syntax supported by the associated DB.

• Data source: consists of the data the User wants to access and its associated management system and network communications (if any) used to access it.

When making a connection to a DB, ODBC uses a Data Source Name (DSN). Each DSN fully specifies the DB including the identity of the ODBC driver and whatever driver specific information it requires.

The ODBC Administrator is a desktop program that configures and manages data sources. The User can run it to create a DSN and either select an existing DB file or create a new one. The ODBC Administrator prompts the User for the driver to use and then uses it while prompting for driver specific information and completing its operations.

The DSN forms part of a connection string which may include other optional parameters such as username and password.

Note:
For all ODBC connections that the ON hostid clause of the EXTERNAL OPEN command is not used. All the information it needs is supplied by the DSN any other parts of the connection string.

In the following sections there are some general details of ODBC, its components and facilities. For more information, refer to the appropriate ODBC document or help file.