JPernLite: extensible transaction services for the WWW

Concurrency control is one of the key problems in design and implementation of collaborative systems such as hypertext/hypermedia systems, CAD/CAM systems, and software development environments. Most existing systems store data in specialized databases with built-in concurrency control policies, usually implemented via locking. It is desirable to construct such collaborative systems on top of the World Wide Web, but most Web servers do not support even conventional transactions, let alone distributed (multi-Website) transactions or flexible concurrency control mechanisms oriented toward team work-such as event notification, shared locks, and fine granularity locks. We present a transaction server that operates independently of Web servers or the collaborative systems, to fill the concurrency control gap. By default, the transaction server enforces the conventional atomic transaction model, where sets of operations are performed in an all-or-nothing fashion and isolated from concurrent users. The server can be tailored dynamically to apply more sophisticated concurrency control policies appropriate for collaboration. The transaction server also supports applications employing information resources other than Web servers, such as legacy databases, CORBA objects, and other hypermedia systems. Our implementation permits a wide range of system architecture styles