GRDDL provides a standard way to extract RDF representations from XML documents through transformations. It addresses the need for machines to consume semantics from web content by specifying how to "glean" or harvest RDF from XML dialects like XHTML through deterministic transformations. GRDDL transformations take an XML document and return an RDF graph, with the goal of providing a faithful semantic interpretation of the information in the source document. Implementations of GRDDL orchestrate parsing data, resolving representations, applying transformations, and handling the recursive nature of extracting and transforming semantics.

1. GRDDL
The Why, What, How, and Where
Chimezie Ogbuji
Cleveland Clinic Foundation

2. GRDDL: The Acronym
 Gleaning
 Resource
 Descriptions (from)
 Dialects (of)
 Language
 Rather long and intimidating

3. GRDDL: By Deconstruction
 Wordnet Definition of Glean:
◦ (gather, as of natural products)
◦ Synonyms: reap, harvest.
 Resource Description Framework (RDF)
◦ Logical assertions
 Dialects of Language
◦ XML document families (XHTML, for instance)

4. GRDDL: By Analogy
GRDDL can be thought of
as a protocol for sowing
semantics in web content
for later harvest.

5. The Why
 Vast amount of latent semantics in markup
<span>Chimezie Ogbuji<span>
 Web content today is primarily built for
human consumption
 Text indexing will only get you so far for
document retrieval
 If machines are meant to harvest RDF from
documents, reproducible protocols are
needed

6. The Why (Cont.)
 Microformats, eRDF, and RDFa
 Specific to a particular family of
documents
 XHTML and HTML
 If the goal is machine consumption, the
bar needs to be raised beyond XHTML

7. The Why (Cont.)
 It seems easy to forget that XHTML is
indeed an XML dialect
 You would think the (X) would make
that obvious
 What was needed was a standard way to
harvest RDF that is applicable to all XML
dialects

8. The What
 Faithful rendition
 Transformations
 GRDDL result
 Source documents
 GRDDL-aware Agents

9. Faithful Rendition
“By specifying a GRDDL transformation, the author of a document
states that the transformation will provide a faithful rendition in
RDF of information (or some portion of the information)
expressed through the XML dialect used in the source document.”
 Licenses an author-certified interpretation of
an XML document
 A powerful paradigm for messaging
 See David Booths “RDF and SOA”
 http://www.w3.org/2007/01/wos-papers/booth

10. GRDDL Transformations
 Functions that take an XML document and
return an RDF graph
 Transformations can be written in any
particular language
 The “reference” transformation language is
XSLT
 “[XSLT1] is the format most widely supported by GRDDL-
aware agents as of this writing […] is specifically designed to
express XML to XML transformations and has some good
safety characteristics”

11. Other Transformation Languages
 “.. technically Javascript, C, or virtually any
other programming language may be used to
express transformations for GRDDL”
 However, these transformations need to be
deterministic in order to ensure the result is
a faithful rendition
 Hence, they must be functions

12. GRDDL Result
 The result of applying the transformation is
an RDF serialization
 The RDF graph that corresponds to the
serialization is a GRDDL result of the
original document
 The “reference” result format is RDF/XML
 Other formats can be used (Turtle, N3,etc.)

13. GRDDL Source Documents
 The class of documents for which GRDDL
defines a way to extract a result graph:
 XML Documents
 XML Namespace Documents
 Valid XHTML
 XHTML Profiles

14. GRDDL Source Documents

15. GRDDL: XML Documents
 GRDDL Namespace (grddl prefix)
http://www.w3.org/2003/g/data-view#
 transformation attribute
<?xml version=“1.0” encoding=“UTF-8”?>
<root
xmlns:grddl='http://www.w3.org/2003/g/data-view#’
grddl:transformation=“.. path to transform ..”>
… XML content ..
</root>

16. Namespace Documents
“Transformations can be associated not only with individual
documents but also with whole dialects that share an XML
namespace”
 A GRDDL source document lives at the
location of the namespace URI of the root
element (the namespace document)
 The GRDDL result of the namespace
document has a statement of the form:
?nsDoc grddl:namespaceTransformation ?txDoc
• txDoc is the location of a transformation
applicable to such XML documents

17. Valid XHTML Documents
<html xmlns="http://www.w3.org/1999/xhtml">
<head
profile="http://www.w3.org/2003/g/data-view">
<title>Some Document</title>
<link rel="transformation"
href=”.. path to transformation .. " />
...
</head>
…
</html>
 Refers to the GRDDL XHTML profile
 Licenses the interpretation of
rel=“transformation” links

18. XHTML Profiles
“Adding a GRDDL profileTransformation assertion to a profile
document is much like adding a namespaceTransformation
assertion to a namespace document”
 A GRDDL source document lives at the
location of the profile URI an XHTML
document
 The GRDDL result of the profile document
has a statement of the form:
?profileDoc grddl:profileTransformation ?txDoc
• txDoc is the location of a transformation
applicable to such XML documents

19. The How
 GRDDL builds on existing XML & RDF
standards
 An implementation mostly needs to
orchestrate:
 Parsing of data representations
 Resolving representations from web locations
 The necessary XML processing to peek into and
harvest RDF from the various sources
 The highly recursive nature of GRDDL

20. Technological Overlap

21. Anatomy of a GRDDL
Implementation: GRDDL.py
 A reference implementation from scratch
 650 LOC
 RDFLib, 4Suite-XML, and Python control logic
 A layered approach
 Core module that handles transformations
 One module per source type stacked on top of the
core
 A top layer that orchestrates the recursion and
identification of which ‘class’ a source document
belongs to

22. GRDDL.py Core

23. Component Stack

24. The Where
 GRDDL services online:
 http://triplr.org/ (Stuff in, triples out)
 http://www.w3.org/2007/08/grddl/ (W3C GRDDL
Service)
 Primary GRDDL implementations:
 Redland
 GRDDL.py
 Virtuoso
 GRDDL Reader for Jena
 RDFa is most common GRDDL source
content format in the wild

25. Hidden Value Proposition
 Supports separation of concerns:
 XML for messaging, data collection,
structural validation
 RDF for Expressive assertions, inference,
etc.
 A way to invest in data richness and
accessibility

26. GRDDL Usecases
 Embedding scheduling assertions on
personal pages
 Using GRDDL for extracting RDF from XML
medical record documents
 Cleveland Clinic use case (clinical
research)
 Aggregating web-based product reviews
 Embedding web service descriptions
 Adding semantic assertions to XML schemas
 Embedding semantic assertions to Wikis