Enabling Unambiguous GRDDL Results David Booth <dbooth@hp.com> Presentation to GRDDL Working Group, 27-June-2007 This document: http://dbooth.org/2007/grddl/ambiguity2.ppt

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

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

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

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

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

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

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

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

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

BACKUP SLIDES 16 May 2019

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

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

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