Chapter 6 - Datalinks

Abstract

This chapter discusses a new Structured Query Language (SQL) facility, called datalinks (including a new data type, DATALINK), that allows the substantial control over the security, consistency, and even recoverability of non-SQL data—even when there is no need to access that data using SQL statements. Datalinker is a new software component that mediates between the applications, the SQL server, and the file manager to protect the contents of referenced files. But SQL is the only interface that applications use to access data. Even today, there is probably more data stored in ordinary files, hierarchical database systems, and network (CODASYL) database systems than in SQL database systems. The application environment includes many programs that access such data using some application programming interface (API) other than SQL that is referred as the native API of the data. SQL/MED provides a facility, called datalinks that gives the ability to bring non-SQL data under the control of an SQL database management system without requiring that one moves his or her data into the SQL databases. Datalinks permits one to exercise control over certain aspects of non-SQL data through a cooperative relationship between SQL server and external data's native manager; that cooperative relationship is provided through the services of a datalinker.