Paul, OSLC is not really defining a new programming model. Instead it is adopting the programming model of the Web. An OSLC client should therefore behave like a Web browser. There are plenty of bad HTML pages and broken links on the Web, yet browsers don't crash. They handle pages as best they can and provide error messages when they can't proceed.
The same applies to OSLC servers. They need to be developed on the expectation that they'll get bad requests. Regards, ___________________________________________________________________________ Arthur Ryman, PhD, DE Chief Architect, Project and Portfolio Management IBM Software, Rational Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063 From: Paul Komar <[email protected]> To: [email protected] Date: 01/06/2011 04:14 PM Subject: [oslc-core] What can an OSLC spec claim? What can a client assume? Sent by: [email protected] Last month Martin Nally wrote " I think this confirms that the only safe option for a client is to assume nothing. I think the spec should say this." Can you please help me understand how a person can implement a client of a service whose specification is based upon that much ambiguity? (I got the impression from reading some historical notes from WebDAV client implementers that while the spec might be written to allow varying degrees of sophistication of service implementations, they would have preferred a tighter, more constrained spec.) Arthur Ryman replied to "I agree that clients should be able to gracefully handle unexpected responses." It seems to me that clients can gracefully decline to provide the desired behavior when the server doesn't give the client what it needs. Consider a use case where a client must get information from a service and then use the information in the response to get more information (possibly from another service). If the first service does not provide the requested information, then the client cannot complete the use case. Also, I'm curious to learn how to write good compliance tests if the client can assume nothing. While the Rest/OSLC world may want to be more flexible than the UML world (with its effective requirement of transitive closure across domains, as Martin also wrote about), OSLC services must provide the information in a consumable way, right? I thought that the Restful way to handle version upgrades was to use media types that provided compatible ways to add information in subsequent versions, but allow older/smaller clients to use the older/smaller content. It seems to me that a Rest/OSLC client might have to have a "broader" expectation of valid responses than an client from the UML world. (Perhaps there's an equivalence class of useful responses?) In summary, I wonder if Martin or Arthur could write up a pattern for good OSLC client implementations. Maybe there would be a rule like " don't validate that the response is what you expect, instead look in the response for the information that you require"? -- Paul Komar Jazz/RTC SCM Developer Rational Software IBM Software Group Littleton, MA_______________________________________________ Oslc-Core mailing list [email protected] http://open-services.net/mailman/listinfo/oslc-core_open-services.net
