RDFa annotates pages not elements

[michael-n-cooper]

I recently submitted a pull request #50 to describe how to use the personalization semantics vocabulary in HTML Microdata and RDFa. I have since been told by a RDFa expert that RDFa does not add semantics to the element it is used on; instead, it describes how to use content from that element to add semantics to the page as a whole. This would mean that RDFa would not be a useful metadata language for most of the use cases we have for personalization semantics. I still need to learn more about this but wanted to log an issue.

If RDFa only annotates the page as a whole, then we should explore if there are features of personalization semantics for which that is useful. My guess would be that personalization at a page level would be a different kind of module from the others, and we might say RDFa could be used only for that module. This is likely to benefit use cases that impact search engines (e.g., pointers to alternate versions of content and the nature of the alternative) rather than direct user experience in user agents.

[csarven]

It is not true that "RDFa only annotates the page as a whole". RDFa can annotate any arbitrary information inside host languages like (X)HTML, and various XML-family languages, e.g., SVG, MathML.

The subject and object of the statements can be about anything, including a reference to fragment within the document, or an external reference, simply any URI, or even a blank node (an unnamed local identifier).

See examples in https://www.w3.org/TR/rdfa-core/

https://www.w3.org/TR/ldn/ , https://csarven.ca/ , https://solidproject.org/ED/protocol , https://csarven.ca/linked-research-decentralised-web , to name a few from the wild.

This HTML+RDFa snippet from https://solidproject.org/ED/protocol :

<dt>Accessible Applications</dt>
<dd about="" id="accessible-rich-internet-applications" rel="spec:advisement" resource="#accessible-rich-internet-applications"><span property="spec:statement">To help assistive technologies to provide a consistent user interface and understanding of the objects, it is <span rel="spec:advisementLevel" resource="spec:StronglyEncouraged">strongly encouraged</span> to follow the <cite><a href="[https://www.w3.org/TR/wai-aria-1.2/](view-source:https://www.w3.org/TR/wai-aria-1.2/)" rel="cito:citesAsAuthority">Accessible Rich Internet Applications</a></cite> [<cite><a class="bibref" href="[#bib-wai-aria-1.2](view-source:https://solidproject.org/ED/protocol#bib-wai-aria-1.2)" title="Accessible Rich Internet Applications (WAI-ARIA) 1.2">WAI-ARIA-1.2</a></cite>] recommendations.</span></dd>

has equivalent serialization in Turtle:

<https://solidproject.org/ED/protocol>
  spec:advisement <https://solidproject.org/ED/protocol#accessible-rich-internet-applications> .

<https://solidproject.org/ED/protocol#accessible-rich-internet-applications>
  spec:advisementLevel spec:StronglyEncouraged .
  spec:statement "To help assistive technologies to provide a consistent user interface and understanding of the objects, it is strongly encouraged to follow the Accessible Rich Internet Applications [WAI-ARIA-1.2] recommendations."@en .
  cito:citesAsAuthority <https://www.w3.org/TR/wai-aria-1.2/> .

It is expressing something like: the document has an advisement, and that advisement has level of strongly encouraged, with a human-readable description, and it cites WAI-ARIA 1.2 as authority on the subject matter.

SVG+RDFa example:

https://www.w3.org/TR/ldn/linked-data-notifications-overview.svg

See the underlying statements:

http://rdf.greggkellogg.net/distiller?command=serialize&format=rdfa&output_format=turtle&url=https:%2F%2Fwww.w3.org%2FTR%2Fldn%2Flinked-data-notifications-overview.svg

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