RE: FPWD comment - literals, data types and language tags

I mean hash URIs in this sense:

http://www.w3.org/TR/cooluris/#hashuri


Here’s an example where the body is a blank node:

<anno1>
                a oa:Annotation ;
                oa:hasBody [
                                # This is a blank node
# foo
]  .

As an alternative, the body could be given identity by adding a hash fragment on the annotation URI:

<anno1>
                a oa:Annotation ;
                oa:hasBody <anno1#foo> .

<anno1#foo>
                # foo
                # This is not a blank node

In principle, it seems like the latter resource could even be published separately. If the <anno1> resource wants to mash it in with its response for convenience, that should be a reasonable thing to do.

<anno1>
                a oa:Annotation ;
                oa:hasBody <foo> .

<foo>
                # foo
                # This is a separately published resource, but is included in the published <anno1> response for convenience.

From this vantage point, it appears that the oa:EmbeddedContent is just a way to tunnel HTTP protocol information like media-type and language (which could be content-negotiable in the latter case). Whether this tunneling is encoded as a data: URI or in vocabulary seems like a tossup in terms of complexity and mockery.

Jeff

From: Robert Sanderson [mailto:azaroth42@gmail.com]
Sent: Sunday, December 14, 2014 10:39 PM
To: Young,Jeff (OR)
Cc: Ivan Herman; Antoine Isaac; W3C Public Annotation List
Subject: Re: FPWD comment - literals, data types and language tags


oa:EmbeddedResource is a class that is typically applied to blank nodes.  The implication of the class being that the representation of the resource is present as the literal object of the rdf:value predicate.  So they would be achieving that purpose with a blank node.

By hash URI, do you mean a data:// URI? That could be done, but seems unnecessarily complex and really makes a mockery of the web architecture (IMO).

The warning bells point was that one of the reasons we have literal bodies is the anti-RDF, anti-modeling crowd want them.  So to then have to explain a bunch of special cases due to RDF constraints because allowing language tags/data types, seems even more counter-productive.

Rob




On Sun, Dec 14, 2014 at 6:54 PM, Young,Jeff (OR) <jyoung@oclc.org<mailto:jyoung@oclc.org>> wrote:
I'm also curious about the need for EmbeddedContent as a resource type. If a data publisher *wants* to embed a "content resource" alongside another resource(s), they could (but shouldn't be required to) achieve that purpose with a blank node or a hash URI.

Are the RDF warning bells a sign that it isn't being assumed for this application?

On Dec 14, 2014, at 9:35 PM, Young,Jeff (OR) <jyoung@oclc.org<mailto:jyoung@oclc.org>> wrote:
This seems similar to how SKOS-XL"upgrades" strings to things: http://www.w3.org/2008/05/skos-xl#Label


SKOS-XL labels are heavyweight in comparison to SKOS labels, but some of the weight can be "hidden" in the JSON-LD context. That is assuming people publish and consume the "hidden" level correctly.


On Dec 14, 2014, at 8:38 PM, Robert Sanderson <azaroth42@gmail.com<mailto:azaroth42@gmail.com>> wrote:

Hi Ivan, Jeff,

Firstly, I agree wholeheartedly with Jeff's position that we shouldn't be mixing up model and serialization ... but that's exactly what the requirement is for string literal bodies.

The model requirement would be:  I want to embed a textual comment within the annotation as the body.  That's precisely what the EmbeddedContent resource does (and ContentAsText used to do).  Indeed, when the requirement was brought up at the CSV WG (for example) the negative reaction was not to the model, but to the serialization as a JSON object instead of a string.

The requirement to have language associated with a string is also perfectly reasonable, and already accounted for.   The requirement to have format associated with a string, ditto.  And the clincher is having both format and language is not possible with literals in RDF, and must be done with a resource.

So, if we want to not talk about serialization, that's fine, but the answer is to get rid of string literals and have a single, coherent model for embedded content.

If value was mapped to @value and language to @language, that would work until someone wanted to associate a format with the content. And then it would break spectacularly.

If we allowed language tagged and (separately) data-typed literals we would have the following possible combinations all being legal that clients would have to take into account:

"body": "string"
"body": {"@value": "string"}
"body": {"value": "string"}
"body": {"@value": "string", "@language": "en"}
"body": {"value": "string", "language": "en"}
"body": {"@value": "<b>string</b>", "@type": "rdf:HTML"}
"body": {"value": "<b>string</b>", "format": "text/html"}
// Not @value, @language, @type !
"body: {"value": "<b>string</b>", "language": "en", "format": "text/html"}

Are you SURE that is preferable to a single consistent model?  Do you REALLY want us to have to explain that the @value/@language/@type combination is not allowed because RDF (oh oh, warning bells!) doesn't allow it and hence developers need to deal with lots of special cases?  That is the consequence of going down this route.

I am strongly against it.

Rob


On Sun, Dec 14, 2014 at 1:18 AM, Ivan Herman <ivan@w3.org<mailto:ivan@w3.org>> wrote:
Jeff

I think this can be mitigated, actually. We need again a JSON-LD expert but I would expect the @context to be able to map a "value" to "@value" and "language" to "@language", if we really do not want to impose the usage of "@" signs for special properties. Ie, we do not have a different JSON serialization.

If this is so, then, in fact, we solve both issues. The JSON-LD idiom

"body" : {"value": "hi", "language": "en"}

would, in fact, be equivalent to

"body" : {"@value": "hi", "@language": "en"}

which means that the value of "body" is a language string, not a separate resource. Which is exactly what Antoine wants. In fact, this is one of the cases where the Turtle serialization is way more readable, because it would be

<> oa:body "hi"@en .

_If_ the @context cannot be used for the mapping above, then I fully agree with Jeff's reaction. We should then use the "@value" and "@en" terminology in JSON-LD (I do not think that would really create major issues of acceptance, frankly), and thereby avoid a duplication of concepts. As a bonus, we also solve Antoine's issue for free:-)


Ivan


> On 14 Dec 2014, at 04:05 , Young,Jeff (OR) <jyoung@OCLC.ORG<mailto:jyoung@OCLC.ORG>> wrote:
>
> The serialization may look "the same" to human eyes, but here's the spec for JSON-LD:
>
> http://www.w3.org/TR/json-ld/#string-internationalization

>
> It would be a shame if Web Annotations invented another JSON serialization. What would that one be called?
>
> http://blog.ldodds.com/2010/12/02/rdf-and-json-a-clash-of-model-and-syntax/

>
> On Dec 13, 2014, at 8:21 PM, Robert Sanderson <azaroth42@gmail.com<mailto:azaroth42@gmail.com>> wrote:
>
>>
>> Hi Antoine, all,
>>
>> To me the only value of literal bodies is to enable a simple string.  As soon as you add data types or language tags, the complexity and even serialization is the same as using a full resource, almost character for character:
>>
>> Language tagged string:
>>     {"@value": "hi", "@language": "en"}
>>
>> Real (blank node) resource:
>>     {"value": "hi", "language": "en"}
>>
>> The argument against always using a resource, and thereby enabling full OWL reasoning and a consistent model that respects the web architecture, is that people want to have only a string without anything else ... so that's all we allowed.
>>
>> As the model allows for language (and format and other metadata) to be associated with the body using the (preferred) resource method, and we don't want to create multiple ways to do the same thing, I'm against (as you might imagine) allowing language tagged literals.
>>
>> Rob
>>
>>
>> On Sat, Dec 13, 2014 at 7:46 AM, Antoine Isaac <aisaac@few.vu.nl<mailto:aisaac@few.vu.nl>> wrote:
>> Dear all,
>>
>> Congrats for the WD!
>>
>> I'm looking at it now, and I'm really happy with simple bodies.
>> I am not so happy however with the fact that the spec does forbid the use of language tags on simple text bodies.
>>
>> In the OA community, several months ago, there was a discussion about XML-datatypes vs plain-literals-with-language-tags. As Rob reminded me in private mail:
>> [
>> The issue with datatypes and language tags is:
>>
>> * You can't have both at once in RDF, so we need to allow:
>>     {"value": "hi", "language": "en", "format": "text/plain"}
>>
>> * In JSON-LD, the difference between a language tagged literal, and the resource is very confusing:
>> "hi"@en is:  {"@value": "hi", "@language" : "en"}
>> Whereas the blank node just drops the @s:   {"value": "hi", "language": "en"}
>> If we allowed both patterns, we'd be losing any simplicity and understandability gains by having them at all.  So if there's more information than just the value, including format, language, creator, etc, then it has to be a resource following the web architecture.
>>
>> * If the body data type isn't fixed, you would end up with the same situation as language tags, just with @type and format.  So to prevent it we require it to be an xsd:string, which will serialize to just the string in JSON-LD compaction.
>> ]
>>
>> At the time I accepted these arguments. But I think what convinced me then is that there were cases mentioned for literal bodies that would have a different (XML) datatype.
>> Now the FPWD mentions only simple text bodies. So this makes the case for not using plain literals a lot weaker.
>>
>> If I was a fresh reader, it would puzzle me a lot to find the sentence
>> "The string body MUST be an xsd:string and MUST NOT have a language associated with it."
>> And as someone with a key interest in multilingual scenarios, I want to raise again the issue!
>> In fact the current solution makes annotations-with-literals useless in many of the Europeana cases, so I'd rather see a very good case for not enabling language tags.
>>
>> Best regards,
>>
>> Antoine
>>
>>
>>
>> --
>> Rob Sanderson
>> Information Standards Advocate
>> Digital Library Systems and Services
>> Stanford, CA 94305

----
Ivan Herman, W3C
Digital Publishing Activity Lead
Home: http://www.w3.org/People/Ivan/

mobile: +31-641044153<tel:%2B31-641044153>
ORCID ID: http://orcid.org/0000-0003-0782-2704






--
Rob Sanderson
Information Standards Advocate
Digital Library Systems and Services
Stanford, CA 94305


--
Rob Sanderson
Information Standards Advocate
Digital Library Systems and Services
Stanford, CA 94305