INF: Microsoft Open Data Services ODBC Driver

• Microsoft SQL Server, version 6.0

SUMMARY

This article outlines the basic architecture of the Microsoft Open Data Services ODBC Driver. If you need more detailed information regarding this driver and Open Data Services, you should review the SQL Server 6.0 or later "Programming Open Data Services" or "Programmers Reference for Open Data Services" manuals in prior releases of Microsoft SQL Server.

MORE INFORMATION

Open Data Services (ODS) is a component of Microsoft SQL Server that can be used to write extended stored procedures, add audit and security extensions to SQL Server, and also write gateways to other databases such as Oracle or DB2. ODS gateways run as Windows NT services and accept SQL requests from applications using the same Transact-SQL syntax and the same network protocols as Microsoft SQL Server.

The gateway will transform the Transact-SQL to the dialect understood by the target DBMS and then send each request to the target DBMS using its native protocols. When the target DBMS sends the results back, ODS and the gateway translate the results into the format used by SQL Server and forwards the results to the application using SQL Server's network protocols. An ODS gateway therefore is a service that looks like Microsoft SQL Server to an application and can be used by SQL Server applications to access other types of databases without having to be rewritten using the API of that target database.

An ODS gateway application can be written to run against a database that does not have all of the features of Microsoft SQL Server. For example, the target database may not have some of the datatypes or transaction isolation levels supported by SQL Server. Although these missing features do not cause problems for the SQL Server components used by DB-Libary applications, they do cause problems for the Microsoft SQL Server ODBC driver. The SQL Server ODBC driver is highly optimized to run with Microsoft SQL Server and requires that the service it has connected to contains all the features of Microsoft SQL Server. If the Microsoft SQL Server ODBC Driver is used to connect to an ODS gateway that does not have the exact same feature set as a Microsoft SQL Server, the driver will not work properly.

The ODS ODBC driver was developed for use with ODS gateway applications. It has the same architecture and most of the code of the Microsoft SQL Server ODBC Driver, but also allows the developer of the ODS gateway application to compile a resource DLL that tells the ODS ODBC Driver what database features are supported by the ODS gateway. The ODS ODBC driver can then work correctly with the ODS gateway application and ODBC applications. There are both Win16 (ODSGATE.DLL) and Win32 (ODSGT32.DLL) versions of the ODS ODBC Driver. The gateway vendor also has to compile Win16 and Win32 versions of their resource DLL. When you define an ODBC data source for the ODS ODBC Driver, you must specify the name of the resource DLL to load and the connectivity parameters the driver will use to connect to the ODS gateway service.

The ODS ODBC driver is generally distributed by the vendor supplying the ODS gateway application. This is because the driver will not work properly unless it has a resource DLL that correctly describes the feature set of the ODS gateway application. The resource DLL must be supplied by the gateway developer who knows the capabilities of the gateway. In this case, the ODS gateway application vendor provides the primary support for the ODS driver, and if they determine the problem lies in the driver, the vendor will contact Microsoft to work on the issue.

Microsoft does not distribute the ODS ODBC driver with SQL Server because the driver is only useful in connecting to ODS gateways and must be coupled with a resource DLL specific to each ODS gateway. The only time Microsoft provides a copy of the actual ODS ODBC driver is in the Microsoft SQL Server Programmer's Toolkit (PTK). In SQL Server 6.0, this is distributed with the SQL Workstation product, or in the BackOffice SDK that comes with the MSDN Level 3 compact disc.

The driver in the SQL Server PTK is provided as part of the ODS libraries so that ODS gateway vendors can build a resource DLL for their gateway and then distribute the resource and driver DLLs with their gateway. Microsoft does provide a sample resource DLL in the ODS libraries, but this resource DLL can only be used to connect to an ODS service that offers exactly the same feature set as the corresponding Microsoft SQL Server. For example, the sample resource DLL provided in the SQL Server 6.0 ODS libraries can only be used to connect to a Microsoft SQL Server 6.0, or an ODS service which has exactly the same feature set as Microsoft SQL Server 6.0. It cannot be used to connect to any other release of SQL Server because those versions will not have some of the features described in the 6.0 sample resource DLL.

Although developers can use the ODS ODBC driver with the sample resource DLL to connect to a Microsoft SQL Server for testing, clients running in production environments should use the Microsoft SQL Server ODBC driver instead. They should only use the ODS ODBC Driver when connecting to an ODS application.