Applications with Windows clients accessing SQL databases could serve thousands of users, but Internet connectivity brought dramatic growth in the user population. Internet computing is distributed computing in the large and it places a premium on scalable architectures. Scalability is a key requirement for client-server databases, networking software and data access middleware. The Internet model supports large user populations and distributed processing based on platform-neutral technology.

The Internet and Extensible Markup Language (XML) emphasize interoperability, which has influenced middleware and services. Middleware today can provide connections between homogeneous or heterogeneous systems, clients and servers, using diverse operating systems and database platforms. Middleware today can provide connections between homogeneous or heterogeneous systems, clients and servers, using diverse operating systems and database platforms. It can operate in any tier of a multi-tier architecture (figure 1).

After object-oriented programming (OOP) and components became a favored approach to developing software, it was inevitable there’d be a call for data-aware components. These components simplify development by putting a layer of abstraction over SQL application programming interfaces (APIs). Not to be overlooked is the fact that under the covers the components use data access middleware. Components, object libraries and database engines sometimes introduce a performance penalty that’s erroneously attributed to APIs and middleware.

The emergence of XML prompted a move by IBM and Microsoft to resolve interoperability problems with components. They unveiled a computing paradigm that used XML-based Web services to permit the creation of collaborative applications. The new model for collaborative computing using Web services and a services-oriented architecture (SOA) garnered widespread support among leading software and hardware companies and the open source community.

Recognizing the potential of XML, the major database vendors extended their SQL platforms to provide document processing, document queries, XML messaging and integration with Web services.