Open Data Services Architecture

Open Data Services is an interface between server Net-Libraries and server-based applications. It allows you to develop:

• Extended stored procedures that extend the power of Transact-SQL and Microsoft® SQL Server™.
• A server application that accepts and processes Transact-SQL statements sent to it from client applications (SQL Server is an example of an Open Data Services application).

Open Data Services has an API consisting of function calls and macros used to develop Open Data Services server applications using C or C++.

Open Data Services runs on the server. The server Net-Libraries receive client TDS packets and pass them to Open Data Services. Open Data Services transforms the TDS packets into events that it passes to server applications through callback API functions. The server application then uses another set of Open Data Services API functions to send replies back to SQL Server clients. SQL Server is implemented as an Open Data Services application. Open Data Services is started automatically when you start SQL Server.

The main type of Open Data Services applications still written by customers are extended stored procedures. This feature of SQL Server allows you to implement C or C++ functions that can be called directly from Transact-SQL statements. Extended stored procedures can open a connection back to the SQL Server installation that called them, or connect to remote SQL Server installations. Extended stored procedures can include most of the features of Microsoft Win32® and COM applications, and extend Transact-SQL functionality.

In the past, Open Data Services was also used to write server applications, such as gateways, to other database systems. These types of applications have largely been replaced by newer technologies such as:

• Database APIs that support multiple different databases and other data sources, such as OLE DB and ODBC.

  Applications written to the OLE DB or ODBC APIs have little need for a gateway to access different databases.

• The support in SQL Server version 7.0 introduces heterogeneous distributed queries, which allow Transact-SQL queries to pull data from any OLE DB data source without any need for specialized server applications.
• MS DTC, which allows distributed transactions to span multiple databases.
• Windows NT Component Services, for running midtier application logic.

See Also

Programming Open Data Services