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.

A hypercode software engineering environment represents all plausible multimedia artifacts concerned with software development and evolution that can be placed or generated on-line, from source code to formal documentation to digital library resources to informal email and chat transcripts.A hypercode environment supports both internal (hypertext) and external (link server) links among these artifacts, which can be added incrementally as useful connections are discovered; project-specific hypermedia search and browsing; automated construction of artifacts and hyperlinks according the software process; application of tools to the artifacts according to the process workflow; and collaborative work for geographically dispersed teams.We present a general architecture for what we call hypermedia subwebs, and groupspace services operating on shared subwebs, based on World Wide Web technology -which could be applied over the Internet or within an intranet.We describe our realization in OzWeb.