WoT Profiles 2.0 - Strawman Proposal

Hi,

There have been lots of discussions in the past around how Profiles
<https://w3c.github.io/wot-profile/> and Binding Templates
<https://w3c.github.io/wot-binding-templates> should work together, since
in their current form they essentially provide two different (and in some
ways conflicting) mechanisms for defining protocol bindings.

Recently there seems to be a tentative agreement around the idea that the
current protocol binding sections of Profiles could be merged into Protocol
Binding Template documents, as defaults. Profiles could then simply
reference protocol binding documents, but mandate that the defaults are
used by conformant Web Things.

In order to explore this idea further I have created two strawman proposal
documents:

   - Web of Things (WoT) HTTP Protocol Binding 2.0
   <https://docs.google.com/document/d/1msgUZSrniTrgVieU2i_V2804gqvVsHrYByTv-OET1l8/edit?usp=sharing>
   - Web of Things (WoT) HTTP Basic Profile 2.0
   <https://docs.google.com/document/d/1LjBWiqQZXi85gXP2NNckQni5os6dwxW6UDGrZDb3cns/edit?usp=sharing>

The HTTP Protocol Binding 2.0 document specifies both a vocabulary for
describing a custom HTTP protocol binding in a Thing Description, and a
default protocol binding which can be assumed by Consumers for a subset of
operations if a custom protocol binding is not specified. (This results in
better interoperability by default, since all Consumers would be required
to implement the defaults).

The HTTP Basic Profile 2.0 document then takes a simpler approach to
defining a profile, by just referencing the protocol binding document. A
profile would essentially just constrain Web Things to a finite set of
options for each extension point in the Thing Description specification
(specifically: protocol bindings, payload bindings, security mechanisms,
discovery mechanisms, link relation types and semantic contexts).

In order to guarantee out-of-the-box interoperability between conformant
Web Things and Consumers, The HTTP Basic Profile 2.0 basically says that
Web Things:

   - Must use the HTTP Protocol Binding 2.0, and must stick to its defaults
   - Must use the JSON payload binding
   - Must implement at least one of a finite set of security mechanisms
   - Must implement at least one of a finite set of discovery mechanisms
   - Are recommended to limit themselves to a finite set of link relation
   types
   - Are recommended to limit themselves to a finite set of semantic
   contexts

It then says that Consumers:

   - Must support the HTTP Protocol Binding 2.0, at least where defaults
   are used
   - Must support the JSON payload binding
   - Must support a minimum set of security mechanisms
   - Must support a minimum set of discovery mechanisms
   - Should support a minimum set of link relation types
   - Should support a minimum set of semantic contexts

Because normative specifications can not depend on non-normative
specifications, if Protocol Binding documents are to be non-normative then
it seems Profiles would have to become non-normative too.

One approach to this could be to have a registry of profiles (either in the
Thing Description document as has been proposed for bindings, or in a
separate WoT Profiles specification), with each individual profile being a
non-normative W3C Note. The only normative part of Profiles would then be
the definition of the profiling mechanism itself, which could also live in
the Thing Description specification
<https://github.com/w3c/wot-profile/issues/372>, or a separate WoT Profiles
specification.

Note that the HTTP Basic Profile 2.0 strawman proposal does not currently
include the HTTP SSE
<https://w3c.github.io/wot-profile/#sec-http-sse-profile> and HTTP Webhook
<https://w3c.github.io/wot-profile/#sec-http-webhook-profile> profiles for
observing properties and subscribing to events. I would suggest those
profiles could potentially live in separate documents and rely on separate
SSE and Webhook protocol binding documents respectively.

I would be very interested to receive your feedback on these proposals,
either on this mailing list, inline in the documents, or in the issues in
the respective repositories:

   - Profile Mechanism 2.0 <https://github.com/w3c/wot-profile/issues/285>
   - Consider merging Profile protocol bindings into Protocol Binding and
   Payload Binding documents
   <https://github.com/w3c/wot-binding-templates/issues/248>

Regards

Ben

P.S. I would very much like to put myself forward as a new Task Force Lead
for the WoT Profiles Task Force in order to work on this, but I currently
don't have a source of funding to support me in doing that. If you are
interested in the profiles and/or protocol binding topics and your
organisation may be interested in sponsoring that work, I would be
delighted if you could get in touch with me.

-- 
Ben Francis
Founder
Krellian Ltd. <https://krellian.com>