Active Systems

October 1995 - December 1998

Overview

An EPSRC grant, in collaboration with Nortel Technology, Harlow, funded by the Multimedia and Networking Applications (MNA) initiative.

We have shown how asynchronous extensions may easily be added to standard Middleware (which is based on synchronous object invocation). The new, generic paradigm is that of the event with publish, register, notify as the fundamental mode of operation. Asynchronous Middleware is capable of rapid response to events and may be used for many application areas, including:

• Detection of mobile users or computers;
• Response to faults in telecommunications networks;
• Detection of illegal entry by surveillance equipment;
• Detection of suspicious patterns of use of bank, credit or phone cards.

The approach is to use Middleware IDL (Interface Definition Language) to specify the events that a given service is able to detect and notify. Such a service will include a registration method for these events as part of its interface and will publish this in the usual way (in an Interface Trader or as part of ORB services).

Our events are named and parametrised at a fine grain; clients register interest in specified classes of events, using specific parameters or wildcards, and servers then notify them of any occurrence of matching events asynchronously. As a by-product of IDL processing, the stubs to handle event creation and decoding are generated automatically. Access control is applied at registration and notification.

Further work is to design, implement and formalise a prototype composite event recogniser based on finite state machines with multiple activations. This allows patterns of events to be specified and detected. An event algebra and associated language allow clients of the service to indicate composite events to it. Composite event servers will support registration and notification in the standard way as described above.

The following people were involved in the project:

• Jean Bacon
• Ken Moody
• John Bates
• Richard Hayton (PhD and RA until Nov 1996)
• Chaoying Ma
• Andrew McNeil
• Oliver Seidel
• Mark Spiteri

Reports

The one page summary and six-page report to EPSRC are available. The following foils illustrate the main features of the Cambridge Event Architecture (CEA).

• The publish, register, notify mechanism: CEA1, CEA1-commentary.
• Direct and mediated notification: CEA2, CEA2-commentary.
• Composite events: CEA3, CEA3-commentary, example.
• Composition using events: CEA4, CEA4-commentary, example
• Mobile groupware users: example.