1. Enabling Unambiguous GRDDL Results
David Booth Presentation to GRDDL Working Group, 27-June This document:

2. What this issue is about
Given an XML document, what RDF did the GRDDL transformation author intend to denote?
Document receiver needs to be able to determine precisely what graph the XML document was intended to denote
Critical when XML document is a serialization of RDF
GRDDL transformation says how to deserialize
16 May 2019

3. What this issue is NOT about
NOT about desired ambiguity
Transformation author may intend variable results
Can be useful sometimes -- a feature, not a bug
NOT about eliminating ambiguity that the transformation author is willing to accept
NOT about forcing the transformation author to be unambiguous
NOT about requiring the GRDDL-aware agent to actually produce the transformation author's intended results
Users may not need them all, for example
This is only about giving the transformation author the ability to be unambiguous about the intended results if desired
16 May 2019

4. Why this issue matters
A key reason for expressing information in RDF is to be precise
Especially important when an XML document represents a (custom) serialization of RDF
GRDDL is W3C Rec-track standardization effort
Not a throw-away specification!
16 May 2019

5. Proposal 1c (transformation domain)
Proposal: Change input of GRDDL transformation from XPath node tree to representation
Observations:
Reduces unwanted ambiguity problem
Permits transformation author to reduce variability in the "transformation application" step
Simple normative change
No changes to test cases
Partial solution -- ambiguity would remain in the "transformation determination" step
Jeremy's example illustrated this limitation
16 May 2019

6. Proposal 1c Pros & Cons Pros: Cons: Simple normative change
No changes to test cases
Partially addresses the problem
Cons:
Does not fully address the problem
May be less efficient (by reparsing representions), though implementations could optimize by avoiding reparsing
Generic risk of a late change
16 May 2019

7. Proposal 2d (minimal parsing)
Change input of GRDDL transformation from XPath node tree to representation; and
Specify that XPath node tree is as if produced by a non-validating processor (XML spec section 5.1)
Observations:
More fully addresses the ambiguity problem
Simple normative change
No changes to test cases
Does not actually require parsing to be non-validating. But transformation determination would be determined as if the parsing were non-validating.
16 May 2019

8. Proposal 2d Pros & Cons Pros: Cons: Simple normative changes
No changes to test cases
More fully addresses the problem
Cons:
May be less efficient (by reparsing representions)
Transformations could not be specified in external DTDs or external entities.
Generic risk of a late change
16 May 2019

9. Proposal 3c (compromise)
Informative change only
Makes clear that GRDDL implementations are expected to conform to the resolution of W3C TAG issue xmlFunctions-34 and XProc's default processing model if issued.
Does not fix the ambiguity problem now, but in theory would fix it when those are issued.
16 May 2019

10. Proposal 3c Pros & Cons Pros: Cons:
In theory, would fix the ambiguity problem eventually
Cons:
When?
Will GRDDL implementations be updated?
How will existing GRDDL transformations be affected?
16 May 2019

11. BACKUP SLIDES
16 May 2019

12. Variability in results -- current spec
Transformation Determination
Transformation Application
GRDDL Transf.
Select
Representation
Parse
XPath node tree
RDF
XSLT/ other
XML Doc
16 May 2019

13. Proposal 1c: Partial solution
Transformation Determination
Transformation Application
GRDDL Transf.
Select
Representation
Parse
XPath node tree
RDF
XSLT/ other
XML Doc
Reduces problem in "transformation application" step
But not in "transformation determination" step
16 May 2019

14. Proposal 2c: Full(?) solution
Transformation Determination
Transformation Application
GRDDL Transf.
Select
Representation
Parse
XPath node tree
RDF
XSLT/ other
XML Doc
Limits parsing to minimum, non-validating
16 May 2019