xAPI Profiles 2.0 / Alignment to xAPI 2.0: timestamp clarifications

[imartinezortiz]

PR for #269

I couldn't find out the XSD schema for 1.1 so I changed the reference in 084ce900c to link the normative definition. Could be https://www.w3.org/TR/owl-time/#time:inXSDDateTimeStamp another better option ?

This PR has been migrated from FeLungs#15. Copying relevant discussion below.

TODO

• Decide proper schema definition to include as reference material.

I found this xml schema which contains the dateTimeStamp definition but I'm not sure if we link directly to that schema or not.

Within the schema, the targetNamespace field is "http://www.w3.org/2001/XMLSchema" and after reading the documentation, I'm still not sure which is more correct; referencing the 2009 version or the 2001 version.

• https://www.w3.org/2009/XMLSchema/derived.nxsd#dateTimeStamp
• http://www.w3.org/2001/XMLSchema#dateTimeStamp

I'm not sure too. Reading owl time in the documentation they reference to the XSD 1.1 normative reference (HTML document), but in the RDF representation seems that they use http://www.w3.org/2001/XMLSchema#dateTimeStamp

<owl:DatatypeProperty rdf:ID="inXSDDateTimeStamp">
   <skos:definition xml:lang="es">Posición de un instante, expresado utilizando xsd:dateTimeStamp.</skos:definition>
   <rdfs:label xml:lang="es">en fecha-sello de tiempo XSD</rdfs:label>
   <rdfs:comment xml:lang="es">Posición de un instante, expresado utilizando xsd:dateTimeStamp.</rdfs:comment>
   <skos:definition xml:lang="en">Position of an instant, expressed using xsd:dateTimeStamp</skos:definition>
   <rdfs:range>
     <rdf:Description rdf:about="http://www.w3.org/2001/XMLSchema#dateTimeStamp">
       <rdfs:label xml:lang="es">sello de tiempo</rdfs:label>
     </rdf:Description>
   </rdfs:range>
   <rdfs:label xml:lang="en">in XSD Date-Time-Stamp</rdfs:label>
   <rdfs:domain rdf:resource="#Instant"/>
   <rdfs:comment xml:lang="en">Position of an instant, expressed using xsd:dateTimeStamp</rdfs:comment>
 </owl:DatatypeProperty>