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Subject: Re: Fw: [oslc-core] Proposal to remove Link header option from Resource Preview spec
"Providers MAY also provide a Link response header [[RFC5988]] with target URI of the Compact resource and rel value http://open-services.net/ns/oslc#Compact on HTTP GET, HEAD, and OPTIONS requests for resources that support preview, but don't have RDF or JSON representations."
95% right; quibbles
1: some readers will think this means they should/must not provide the link on other methods (silence implies different things to different audiences). I don't see any need to limit it; maybe make these exemplary. If you're feeling minimalist, also drop it down to GET only; get gives you HEAD implicitly, "nobody" uses OPTIONS anyway, and OPTIONS would be allowed (along with PUT, POST, ...) by making whatever we do mention exemplary.
2: to be really complete, should say talk about the context URI; you'd want the default (the effective request URI) on the methods you cited above.
3: If we wanted a create responses to support this (seems reasonable, and mentionable), the context URI there would be the same as the Location header (URI of the newly created resource). Obligatory note from 5988 on that: when the context URI != the recipient has to trust the server to make assertions about the context URI; this is usually true for us, but if POST (Create) to rtc9-foo.tivlab.ibm.com created a resource on rtc-master.ibm.com, it's less obvious. I'd just point to 5988 and minimize any restatement.
4: the rdf/json part is ambiguous. should I read it !(rdf|json) or as !rdf|!json?
5: It's not obvious that we need to limit it by media type; the spec heading didn't suggest to me that it applied to anything other than all resources. It would be completely fair to assert (1) some clients (RDF-aware ones, possibly JSON-aware ones) are likely to prefer it in the content, other clients (those agnostic to media type) are likely to prefer it in the header, and (2) for some media types the header might be the only "sensible"/possible choice... while many formats support encoding of name/value pairs in the content, not all do.
6: Given that clients have 2 ways to expose the preview URI, is there guidance (here or elsewhere) about when to use one vs the other? If not, might be simpler to say "if preview is supported, MUST..."; given the constraints, must-header is the only one that flies for all resources; let it be that the advantage of some media types (like RDF) is that you can get the contents without a HTTP retrieval operation, as a convenience to clients capable of understanding those media types, but you can Always get the link itself via the Link header. There's no harm in also providing it in the content, but it's redundant.
7: on ++responses to++ HTTP GET, HEAD, and OPTIONS requests , and then remove "response" before header in the first part. Link is NOT actually defined strictly as a response header, and LDP (at least) uses it on requests as well.
Best Regards, John
Voice US 845-435-9470 BluePages
Cloud and Smarter Infrastructure OSLC
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