JPernLite: an extensible transaction server for the World Wide Web

Concurrency control is a well-known problem in design and implementation of multi-user hypermedia systems. Most existing systems store data and links in specialized databases (link servers or hyperbases) with a built-in concurrency control policy, typically the conventional atomic/serializable transaction model, usually implemented via locking. But this conventional model may not be appropriate for collaborative hypermedia systems, where the multiple users work together in groups on shared tasks. Further, it is desirable to construct collaborative hypermedia 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 towards teamwork -such as event notification, shared locks and fine granularity locks. We present a transaction server that operates independently of web servers or the hypermedia applications, to fill the concurrency control gap. The transaction server by default enforces the conventional 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.