Chapter 5 - Foreign Servers and Foreign-Data Wrappers

Abstract

This chapter addresses the access of non-SQL data through the Structured Query Language (SQL) server. SQL/MED provides a standardized interface by which SQL servers can access data managed by other servers—including non-SQL data. Such data is external to the SQL server and is thus foreign data. The strategic goal of this standardized interface is support for an open, third-party market place in which developers can publish shrink-wrapped software (called foreign-data wrappers) that accesses specific data sources (called foreign servers) without requiring separate releases for different SQL servers. In other words, the interface allows a single wrapper that supports a particular foreign server to be accessed from all SQL engines that conform to SQL/MED. Several commercial SQL products available today have interfaces that are analogous to the SQL/MED interface. Oracle's Open Transparent Gateway provides a well-documented API that can be used to build software components to access other SQL servers as well as non-SQL data sources. Sybase's Omni Connect serves much the same purpose, as does IBM's former Data Joiner product (now part of DB2 Universal Database).