Heterogeneous Distributed Queries

Distributed queries access data currently stored in SQL Server (homogeneous data) and also data traditionally stored in a data store other than SQL Server (heterogeneous data). Distributed queries behave as if all data were stored in SQL Server. SQL Server 7.0 supports distributed queries by taking advantage of the UDA architecture (OLE DB) to access heterogeneous data sources, as shown in this illustration.

The advantages of heterogeneous distributed queries include:

• Working with providers at various levels.
• SQL query access against non-SQL data sources.
• Dialect independence, meaning Transact-SQL against everyone.
• The same mechanism for distributed RDBMS and heterogeneous nonrelational data.
• Minimizing network traffic by executing as much as possible remotely.

Issues for Oracle Versions 7.x and 8.0

Oracle supports heterogeneous distributed queries with SQL Server through the use of gateways. The SQL Server gateway is not included with Oracle; it must be purchased separately. SQL Server is more cost effective because heterogeneous distributed queries are provided with SQL Server 7.0. Because it uses OLE DB, you can access a wider spectrum of heterogeneous relational databases and nonrelational data providers.