RE: A look at WoT specs from Linked Data and AWWW perspective

Hi Martynas,

thanks for bringing Semantic Web aspects in the discussion. A few comments on my side:

> "base" is not a domain vocabulary property

The TD vocabulary is arguably not a “domain” vocabulary either. It is to me nothing more than a generic model to relate physical world entities with Web resources. That said, I completely agree that defining a base is more of a serialization issue and one should use JSON-LD’s @base.

>> I wonder how can "writability" of any property on the web be a predefined constant?
> My understanding of the “writable” flag is that if it were false it would indicate that a property is not writable by anyone, *regardless* of access rights.

I fully agree with Michael McCool. Another example of such a property is the battery status of low-power devices.

> JSON is only one of the syntaxes -- RDF is the model, and constraints should be based on it.

Not exactly. RDF is the foundation of the TD model, sure. But the schemas embedded in a TD model the data a device exposes, not the TD. That data model can be based on SenML or the BLE GATT specification, for instance. WoT devices typically exchange once a TD and ten, hundred times sensor data. It is important to optimize the latter exchanges; RDF would introduce a significant overhead and is therefore not a good candidate. If it is necessary to merge data and meta-data (e.g. a TD or some SSN description of a system), one would have to perform RDF lifting, which is a pretty well-known procedure (see for instance, RML or SPARQL Generate).

Best,
Victor

From: Henry Andrews [mailto:henry@cloudflare.com]
Sent: Freitag, 6. April 2018 08:22
To: Martynas Jusevičius
Cc: public-wot-wg@w3.org
Subject: Re: A look at WoT specs from Linked Data and AWWW perspective

I cannot speak to why the WoT WG has chosen JSON Schema vs anything else, or whether that choice is likely to change.  JSON Schema is not in direct competition with SHACL or SPARQL.

However, JSON Schema is under active development and investigating paths to standardization through either the IETF or W3C, and we view the WoT WG as a key use case for combining JSON Schema with JSON-LD and other semantic web technologies.

JSON Schema is in the unusual situation of having become a de-facto standard when the draft process stalled for several years.  Usually a technology would be abandoned in such cases, but JSON Schema has proven to have considerably more staying power.

As for reaching full standardization, I will note that picking up a widely implemented and deployed proposed standard with several hundred open issues and shepherding it to completion, including resolving the issues that caused the original editors to abandon it, is not something that one can do instantaneously, even if the IETF or W3C were willing to stamp things as-is.  Which, quite rightly, they are not.

-henry


On Thu, Apr 5, 2018 at 1:18 PM, Martynas Jusevičius <martynas@atomgraph.com<mailto:martynas@atomgraph.com>> wrote:
Hi all,


I can start by admitting that WoT is not my domain. But as a potential implementor of WoT data management systems, I have an interest in the W3C spec.

Coming from the RDF/Linked Data world, I think there is a number of things that should be improved. Below is what I observed during the first reading.


5.2.1 Thing
https://www.w3.org/TR/wot-thing-description/#classes


"base" is not a domain vocabulary property, it is a feature of media types that support relative URIs, such as Turtle, JSON-LD etc., where @base is the syntax for it.

The concept of "base URI" does not belong in the WoT domain nor its vocabulary, it is a matter of orthogonal specification(s).


5.2.3 Property
https://www.w3.org/TR/wot-thing-description/#interactionpattern


I wonder how can "writability" of any property on the web be a predefined constant? What happens if agents with different access rights are interacting with it -- is it not feasible that the writability should depend on the ACL, meaning it can change over time and depending on the request?

Again, it looks like the WoT spec is trying to incorporate bits of orthogonal specifications, in case HTTP and probably W3C ACL.

A property, like any Web resource, can be considered writable if an agent can perform PUT or DELETE on its URI and succeed (200 OK). Otherwise, 401 or 403 should be returned. If the writability needs to be probed before making the actual request, HTTP OPTIONS can be used:
https://tools.ietf.org/html/rfc7231#section-4.3.7



5.2.6 DataSchema
https://www.w3.org/TR/wot-thing-description/#dataschema


JSON Schema is referenced here, yet it is not a W3C standard, nor any kind of standard, as far as I know. Why is it considered safe to be used for formal definitions? Why not use an actual W3C standard such as SHACL or SPARQL? https://www.w3.org/TR/shacl/


JSON is only one of the syntaxes -- RDF is the model, and constraints should be based on it.


Martynas Jusevicius
atomgraph.com<http://atomgraph.com>




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