rdf wg update semtechbiz 2012

Updating RDFDavid Woodco-chair, W3C RDF Working GroupJune 2012

Wednesday, May 30, 12

•Define RDF 1.1

•Break as little as possible.

•Reflect real-world experiences back into the standards.

http://www.w3.org/2011/rdf-wg/

Charter




•Changing the fundamentals of RDF(S) semantics

•Removing current restrictions in the RDF model (e.g., literals not allowed as subjects, or blank nodes as predicates)

Out of Scope


RDF is the data model;

More standard serializations will help show that.

Comment


•RDF 1.1 Concepts and Abstract Syntax

•RDF 1.1 Semantics

•RDF 1.1 Primer

• (Minor changes) RDF/XML Syntax Specification

• (Minor changes) RDF Vocabulary Description Language 1.1: RDF Schema

• (New) Turtle

• (New) N-triples

• (New) JSON-LD

Documents


Users WebCoders

FrameworkCoders RESTifarians Logicians Mathematicians

Thanks and apologies to xkcd

Who’sthat?

Everything canbe a resource

Oh, hey, I didn’tsee you guys all

the way over thereGraphs can’t be labileand I’m not either

Can we just changethe spec so I can

implement it?

XRDF WG


http://xkcd.com/435/

http://xkcd.com/435/

Disclaim

ers


•Turtle, First Public Working Draft, 2011-08-09

•RDF 1.1 Concepts and Abstract Syntax, First Public Working Draft, 2011-08-30

•XSD 1.1 usage

•Lots of lessons learned regarding use cases, concerns and expectations.

Progress


•Current list of resolutions:

http://demo.3roundstones.net/rdf/2012/rdfwg/resolutions.xhtml?view

•Closed issues:

http://www.w3.org/2011/rdf-wg/track/issues/closed

Progress










•Graphs

•Charter: “Standardize a model and semantics for multiple graphs and graphs stores”

•This is the most contentious portion of our work because it has the potential to radically change RDF, which we are not chartered to do.

Challenges


•A “Graph Container” is a container, like a mutable “set” data structure in programming. It holds some RDF triples.

•An “RDF Graph” is an idealized snapshot of a Graph Container; it's a mathematical set of RDF triples.

•A “Graph Serialization” is a particular sequence of characters or bytes which conveys a particular RDF Graph in a language (e.g. Turtle or JSON-LD).

Graphs


•Many RDF users avoid using blank nodes. In some circles, this is considered to be a best practice.

•Some issues raised by the use of blank nodes are how they may be followed (e.g. in SPARQL result sets) or referenced (e.g. within the same RDF document).

•Optionally Skolemize blank nodes when desired.

Blank Nodes


• In situations where bNode identification is needed, systems may systematically transform some or all of the blank nodes in an RDF graph into new, globally unique IRIs (Skolem IRIs).

• For example, the authority responsible for the domain example.com could mint the following recognizable Skolem IRI:

http://example.com/.well-known/genid/d26a2d0e98334696f4ad70a677abc1f6

• Makes bNodes useful in the same way that auto_increment columns in SQL are.

Blank Nodes






• Added new RDF-compatible XSD 1.1 datatypes:

• xsd:duration

• xsd:dayTimeDuration

• xsd:yearMonthDuration

• xsd:dateTimeStamp

New Datatypes


String Literals•All literals are typed. “Typed literal” becomes redundant.

•“foo” becomes syntactic sugar for “foo”^^xsd:string.

• Systems SHOULD silently convert xsd:string data to plain literals on output.

• The RDF WG is recommending to the SPARQL WG and other SemWeb WG’s that they do the same.

• Literals with a language tag now have the datatype IRI rdf:langString.


•XMLLiterals will be optional.

•The lexical space consists of well-formed XML fragments.

•The canonical lexical form is http://www.w3.org/TR/xml-exc-c14n/, as defined in RDF 2004 (no longer requires lexical forms to be canonicalized).

•The value space consists of a set of DOM4 DocumentFragment nodes.

rdf:XMLLiteral


http://www.w3.org/TR/xml-exc-c14n/




rdf:HTML•rdf:HTML literals will be introduced.

•The lexical space consists of the set of Unicode strings.

•The value space consists of a set of DOM4 DocumentFragment nodes.

•Two DocumentFragment nodes A and B are considered equal if and only if the DOM4 method A.isEqualNode(B) returns true.


•Turtle:•Changed very little.•Turtle / SPARQL syntax harmonisation

•N-Triples:•Orginally defined only for RDF test cases, n-triples will be standardized primarily for use as a bulk loading syntax.

•JSON-LD (probably)

New RDF Serializations


•ISSUE-1: Turtle / SPARQL harmonization

•‘.’s and ‘:’ in names in all positions of a local name apart from the first or last, e.g.

ex:first.name / ns:foo:bar•Escape characters in prefixed names, e.g.

ex:resource\/thing123 / ex:thing123\#this•Digits in the first character of local names, e.g.

ex:7tm

(Minor) Changes to Turtle


•Floats require a decimal after the ‘.’, e.g.ex:subject ex:hasValue “18.0” .

(so you no longer need a space before the trailing ‘.’)•Adopted case-sensitive constants for xsd:boolean true and false.



•At risk feature:•SPARQL:


@prefix dc: <http://purl.org/dc/terms/> .

PREFIX dc: <http://purl.org/dc/terms/>

•Turtle:

prefix dc: <http://purl.org/dc/terms/>(case insenstive, like SPARQL)

or


http://purl.org/dc/terms/




•HTML5:

Turtle

•XHTML:

<script type="text/turtle">@prefix frbr: <http://purl.org/vocab/frbr/core#> .

<http://books.example.com/works/45U8QJGZSQKDH8N> a frbr:Work .</script>

<script type="text/turtle"># <![CDATA[@prefix frbr: <http://purl.org/vocab/frbr/core#> .

<http://books.example.com/works/45U8QJGZSQKDH8N> a frbr:Work .# ]]></script>


http://purl.org/vocab/frbr/core#


http://books.example.com/works/45U8QJGZSQKDH8N






•Now UTF-8

•Shifted to IRIs, not RDF URI References

•Media type: application/rdf-triples

•Tied closely to the Turtle grammar

N-triples


•JSON-LD developed away from the RDF WG, now back (see http://json-ld.org)

•JSON-LD is a language capable of serializing any RDF graph, and performing full RDF to JSON-LD to RDF round-tripping.

•Working Draft stage, but more mature than most (e.g. implementations exist)

•Concerns: (Perceived lack of WG JS knowledge)

JSON-LD


http://json-ld.org

http://json-ld.org

JSON-LD{ "@context": "http://json-ld.org/contexts/person", "@id": "http://dbpedia.org/resource/John_Lennon", "name": "John Lennon", "birthday": "10-09", "member": "http://dbpedia.org/resource/The_Beatles"}


http://json-ld.org/contexts/person

http://json-ld.org/contexts/person

http://dbpedia.org/resource/John_Lennon

http://dbpedia.org/resource/John_Lennon

http://dbpedia.org/resource/The_Beatles

http://dbpedia.org/resource/The_Beatles

The RDF Working Group is:

Jean-François BagetThomas BakerAdrien BasseScott BauerAidan BoranDan BrickleyMatteo BrunatiGaoussou CamaraGavin CarothersJeremy CarrollPierre-Antoine ChampinKiu ChingOlivier CorbyRichard CyganiakSouripriya DasLee Feigenbaum

Fabien GandonCharles GreerAlex HallSteve HarrisMichael HausenblasSandro HawkePatrick HayesIvan HermanNicholas HumfreyKingsley IdehenArnaud Le HorsDickson LukoseIvan MikhailovPeter Patel-SchneiderEric Prud'hommeauxYves Raimond

Nathan RixhamGuus SchreiberAndy SeaborneManu SpornyThomas SteinerMouhamadou ThiamTed ThibodeauThomas ViselWilliam WaitesJan WielemakerDavid WoodZhe WuMohamed ZergaouiAntoine Zimmermann


Updating RDFDavid Woodco-chair, W3C RDF Working GroupJune 2012


rdf wg update semtechbiz 2012

Education