Related approaches

Interestingly, there are already several examples of projects based on specific middleware for WWW geared towards integrating coordination. Some of these projects are aimed at improving the World Wide Web itself, some make use of it for specific purposes.

There are three different approaches at extending WWW for middleware applications:

• at the server, having HTTP requests activate CGI applications and return the output as an HTML page. For instance the WWW Linda Toolkit [10] is a simple interface between WWW and a Linda tuple space implementation providing access to a shared tuple space through an HTML form; in [2] a general architecture for integrating DCE middleware components into the WWW through CGI is proposed; in Web* HTML data and TCL script are mixed. Each script invocation is then substituted by its output on the server before sending the document to the client. External services are accessible through the CORBA-compliant Orbix system, which is completely interfaced with the Web* application.

• at the client/browser, having pages returned by the server ``executed'' by local applications (client's clients). For instance, in SHAREd Web [8], several concurrent applications are activated to create a complete collaborative environment for a team of designers working on a project; the WWWinda project [7] is building a flexible, modular WWW browser architecture based on the Linda programming language creating several independent tools, each implementing a different part of the whole WWW browser; some browsers add support for complete general purpose scripting language: HotJava and recent generation Netscape Navigators support Java, the Grail browser (!http://monty.cnri.reston.va.us/grail!) is built and extendible with Python, and the SurfIt! browser (!http://pastime.anu.edu.au/SurfIt/!) supports extensions and applets written in Safe-Tcl.

• at the proxy, having HTTP requests and responses collected and acted upon. For instance, OreO [4] is a proxy toolkit for creating generic filters between unmodified browsers and unmodified servers.