[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: RE: [xdi] on global cross references and the link contract use case
|
Les, I think on this topic we’d make
more progress on a telecon/Webex session – what do you think about trying
to have a special one on this topic next week? That said, I’ll do my best to try answer
your question, “Why does there need to be a distinction between the
methods (the cross-reference method and the GCS delimiter method)?” The short answer: each of these “methods”
represents a separate feature of XRI syntax, and we need both features. The long answer: The first feature, syntactic cross-references,
lets an XRI author reuse a URI or XRI from a different context by syntactically
enclosing it in parentheses. For example: =a*(http://example.com) =a*(+b) =a!(+b) We have a long history of use cases that need
this functionality. John and I had discussion yesterday about whether we could live
without some of that functionality, i.e., we asked, “Do we really need to
allow both URIs and XRIs in cross-references?” It didn’t take long
for us to conclude, “Yes.” We have always needed them to
syntactically encapsulate URIs. But we also have many cases in which we need
them for XRIs. For example, in XDI RDF we need to be able to put any multi-segment
XRI representing an XDI RDF statement inside parentheses in order to turn it
into a new single-segment XDI subject or object. Example: =jbradley/+says/(=drummond/$is$a/=jbradley+friend) This functionality is critical to reification
in XDI RDF (which is a big selling point of XDI RDF because reification is
so hard in standard RDF). Conclusion #1: We need cross-references as
a general capability of XRI syntax. **************************** The second feature, GCS delimiters,
lets an XRI author use an XRI directly in the subcontext of another XRI. As John
pointed out in our discussion of this at the F2F, a subcontext is different than
a cross-reference. A subcontext is when one identifier is used directly in the
context of another. An example in English: international
employment contract signature date Each of these five English words has its
own independent global meaning. Yet when used in an ordered set, each of the
last four take on a special meaning when used in the context of the ones before
it. For example, the ordered set of words “signature date” does not
mean the same thing as either of the individual words “signature”
or “date”. The purpose of the GCS Delimiter proposal is
to support exactly the same functionality in XRI syntax – the expression
of an ordered set of XRIs, each in the subcontext of its precedents. For
example: +international+employment$contract$sig$d Just like in the set of English words
expressed as an ordered set above, this set of XRIs expressed as an ordered set
does not have the same meaning as any of the XRIs individually. For example, the
set of ordered XRIs $sig$d (signature date) does not identify the same resource
as either of the individual XRIs $sig (signature) and $d (date). Conclusion #2: We need ordered sets of
XRIs as a general capability of XRI syntax. **************************** Finally, the crux of the answer to “Why
does a distinction need to be able to be made between the two methods?” is
that neither provides the equivalent functionality of the other. In the first case, ordered sets cannot
provide the same functionality as cross-references because ordered sets do not
allow syntactic encapsulation of identifiers from other contexts. They do not
let a URI be used in the context of an XRI, for example, or permit encapsulation
of XDI RDF statements as shown above. In the second case, cross-references cannot
provide the same functionality as ordered sets because a cross-reference is
explicitly a reference to an identifier in _different_
context. That’s what makes it a “cross-reference” – it references
across two contexts. For example, in the XRI... @cordance*(mailto:drummond@example.com) …the cross-reference (mailto:drummond@example.com)
is a reference to a URI rooted in the mailto: context. However in an ordered set, you are not
referencing across contexts. The context is the ordered set itself. For
example, in $sig$d, the context for $d is $sig. That’s what makes it an
ordered set. ***************************** Hope this helps, =Drummond From: Chasen, Les
[mailto:les.chasen@neustar.biz] Yes I did. I still fail to see a reason for the
distinction. Saying that xdi requires this precision does not help me
understand why the distinction is needed. I repeat, these are all
examples of putting a global xri into the context of another. Why does a
disinction need to be made between the methods? I guess I also wonder why
multiple methods are needed but for now I'll be happy to understand why there
needs to be a distinction between them. |
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]