Heterogeneous query processing through SQL table functions

In today's IT infrastructures, data is stored in SQL databases, non-SQL, databases, and host databases like ISAM/VSAM files. Non-SQL databases are specialized data stores controlled by applications like spreadsheets, mail, directory and index services. Developing applications accessing a variety of different data sources is challenging for application developers due to different environments, APIs, bindings, etc. 20 years ago, SQL was created to ease the life of database application developers and provide a uniform way for accessing data which is stored in SQL databases. The paper describes an implementation of table functions and its usage for accessing data stored outside SQL databases in diverse external data stores. Table functions are compliant with the relational data model, and therefore fit into the well established SQL language. The table-function architecture is open, and allows the deployment of generic data access infrastructures such as Microsoft's OLE DB or Java's JDBC (G. Hamilton et al., 1997). The paper describes a prototype implementation of OLE DB table functions with advanced query optimization techniques. The prototype is based on IBM DB2 UDB relational database system.