PPT Slide
This demonstration of the WebTrader illustrates
- service binding and rebinding
- trader federation
In the demo, trading ads exist for a variety of components (e.g., service agents, clients, and WebTraders). Metadata including color and cost is included in the ads. A Blue client, for example, asks the USA WebTrader to locate a Blue agent implementing a particular interface and with zero cost, if possible. One is found and bound, and the client makes use of the agent. When the agent unexpectedly dies, the WebTrader is consulted again by the client, in case the “state of the world” has changed. It gets back a new list of agents, sorts them by cost, and goes down the list trying each agent until it finds one that works. If the WebTrader fails to respond, the client can fall back on its cached list of previously found agents. When the Yellow client asks the USA WebTrader for Yellow agents, the WebTrader’s initial search turns up none, as it only consults a domain that indexes ads of Red, White, or Blue agents. However, it does find an ad for a WebTrader that knows about Yellow agents, and so passes on the original client query to the Euro WebTrader, which finds a Yellow agent, passes it back to the USA WebTrader, which passes it back to the client, which then uses it to connect to the agent.
At the right in the figure is shown a service advertisement in XML.