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Re: [dxwg] Definition of "Schema" (as opposed to profile)

From: kcoyle via GitHub <sysbot+gh@w3.org>
Date: Sat, 19 May 2018 06:14:11 +0000
To: public-dxwg-wg@w3.org
Message-ID: <issue_comment.created-390382904-1526710449-sysbot+gh@w3.org>
I'm not sure what problem we are attempting to solve here. For content negotiation, we need
1. an identifier that allows access to the resource
2. media type information that informs the ingesting software what it needs to know in order to read/parse the file that it receives
3. a profile name that can be offered or accepted

About what technology solution the contents of the resource conform to, as Andrea says "it can rather be inferred by the format or the "standard" (XML Schema, SHACL, etc.) the profile definition conforms to". This will be coded in the received resource and therefore does not need to be provided in the negotiation itself. Also note that there is not a bright line between human and machine-readable - cf. XML -> XSLT for the exposition of human-facing documentation carried in the XML file.

The new requirement ( point 3 above) as requested in ID5.2 is for "A profile captures additional structural and/or semantic constraints in addition to the media type." What I don't see in the use cases is how such a profile will be addressed in the http header, other than by name. From ID5.2:

"Clients and servers should be able to indicate their compatibility and/or preference for certain profiles. This enables clients to request a resource in a specific profile, in addition to the specific content type it requests. A client should be able to determine which profiles a server supports, and with which content types. A client should be able to look up more information about a certain profile."

The <a href="https://profilenegotiation.github.io/I-D-Accept--Schema/I-D-accept-schema#rfc.section.3">IETF proposal</a> doesn't appear to resolve this either.

Key here is that we are not at any point defining a machine language for profiles, and none yet exists, so it is not really possible to reference such a language or the lack thereof (e.g. "human-readable"). This also makes it difficult to refer to functions like modularity (ID5.3), inheritance, etc. because those are inherently technology-dependent. All that appears to be on the table is a way to negotiate with the indication of additional information about the resource, that is, to be able to give a name to a profile that is recognized by client and server. So far no mechanism for making those names themselves known (like MIME types are known) has not been defined, and it seems to me that this is an important element that makes thinking about the profile description quite difficult.



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