doc.Index.index.uim.vdb Virtuoso's federated database engine provides transparent access to relational data residing on any ODBC/JDBC accessible DBMS. Tables from any number of such databases may be linked into a Virtuoso schema, making them indistinguishable from tables stored in the Virtuoso engine itself.The SQL-92 implementation takes location into account for optimization and hides SQL dialect differences between linked DBMS's from applications and developers. Queries and stored procedures may span an arbitrary number of data sources, using two phase commit where appropriate.Virtuoso is ideal for presenting a seamless collection of disparate legacy systems, for use by reporting tools or web services making Virtuoso the natural place for hosting application integration logic working with data in different schemas and databases.Virtuoso Virtual Database provides the following benefits:Transparently accessing heterogeneous database with a single client and login, using a single SQL-92 compliant language. Policy based security for data access, providing find-grained control over what data is visible according to which user account is accessing which tables from which application/site. These measures are transparent, taken and enforced by virtuoso, not requiring policy security on target systems. Replication between Virtuoso and other DBMS's., Bi-directional replication is supported between Virtuoso and Oracle, DB2 and MS SQL Server. For single-database operations, there is practically no performance overhead since operations are passed through to the remote database whenever possible. For distributed queries, processing the query through Virtuoso is generally more efficient than processing it at the application or application server layer since Virtuoso adds intelligent access path optimization and advanced techniques such as hash joins. Locating application server level logic inside Virtuoso through Java or .NET hosting is still more efficient than using a separate application server process. This logic may then be accessed through Virtuoso's web services protocols suite.Available the Enterprise Edition; For distributed transactions , Virtuoso can be a transaction client and resource manager for MS DTC (Microsoft Distributed Transaction Coordinator) and resource manager for XA