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Message:

URLs for Backwards Compatibility with Web Pages

Posted by Bill Venners on September 18, 2000 at 6:55 PM

> I find the concept of accessing Jini services using URLs somewhat alarming. In your proposal for a URLName entry, you suggest that "cyberspace aware" services need to special maintainance by the administrator of Jini lookup service (URL names need to be unique within a lookup service). Accessing Jini services needs to be automatic and manual intervention should be as required as infrequently as possible. I agree with your overall premise that *some* Jini services ought to be accessible using URLs - but - this ability should not affect the Jini infrastructure itself. Rather the URL to service binding should happen on top of Jini and not affect the system's dynamic nature.

> The link between URLs and Jini services should be completely decoupled from the Jini lookup. You do mention in your documentation that a cyberspace service should exist. I think that this service should be in charge of mataining a URL to service mapping. It could act as more "static" lookup service (I dont mean static in a bad way). Services are not discovered dynamically; they are discovered by direct URL reference.

Thanks for your comments. The ability to access a Jini service
via a URL is necessary to enable web pages to link to Jini
services. In the cyberspace demo, I showed a way Jini services
and service UIs could be launched by clicking a link in a web
page. In the demo, only http: URLs were used.

I agree with you that a URL that points to a Jini lookup service
is a bit suspicious, given that lookup services are geared
towards a dynamic network, but some services likely will be
relatively stable citizens of certain lookup services. Such
services could conceivably be pointed to via a jini: URL. That's
what URLName is intended for. There currently exists a jini:
URL for which no standard use of the filename portion of the
URL exists. URLName is a proposed use of that filename portion.

On the other hand, what we've put in the Place API is an
interface called Link, which may be more to your liking. The idea
is to raise the level of abstraction of the URL. A Link is
an object that flies across the network to the client. The client
can ask a Link to get a resource. A Link could do fancy things
like multicast discovery, performing lookups by type, sorting
through multiple matches, and so on -- things that would be
very dynamic and very difficult to express in a URL.

See http://www.artima.com/jini/cyberspace/index.html.

bv