Is this what Web 2.0 is all about? If so, maybe it's not such a
bad thing.
Outline
A history of (X)HTML and the Web
Toward data integration, Web style
Semantic Web * iCalendar = RDF Calendar
GRDDL: Semantic Web data in XHTML
hCalendar and microformats
hCalendar * GRDDL = RDF Calendar
Microformats + SPARQL
Microformats + OWL, rules
Objective: making it cost-effective to
record and share knowledge formally, i.e. so that computers can
manipulate it.
Getting into the Web
What was the tipping point— the killer app—for you?
for Tim Berners-Lee's colleagues at CERN: a cross-platform phone
directory
for me at Convex in 1991: a nifty hypertext system design:
Newsgroups: alt.hypertext
Subject: WorldWideWeb: Summary
Date: 6 Aug 91 16:00:12 GMT
WorldWideWeb - Executive Summary
The WWW project merges the techniques of information retrieval and hypertext to
make an easy but powerful global information system. ...
in the early 1990s: NCSA What's New
these days: maps, auctions, wikipedia, webmail, ...
Getting into the Web: downhill steps
To grow, start with some actual value plus lots of
potential value and a downhill path for contributors:
for a little investment
Note: licensing and legal agreements are not little.
a big return
due to network effects
Scaling
yes, scalability to 10^9 nodes and up is important
but so is scalability down to families and scout troops
Architect for participation -- Tim O'Reilly @ W3C's 10 anniversary
Web Basics: URIs, HTTP, ...
So what makes all that work? Much of it is a story for another day.
The experience of the CSS working group, with the CSS1 Test
Suite, and the many compliant and interoperable implementations
that followed, demonstrated fairly clearly that a simple test
suite is far far better than none at all.
convert $testcase.ics to temporary $testcase-actual.rdf
Use RDF graph comparison to check actual results vs. expected results
to test RDF -> .ics
w.r.t a known-good .ics -> RDF tool:
convert $testcase.rdf to $testcase-temp.ics
Use the known-good tool get $testcase-actual.rdf
Use RDF graph comparison to check $test-case-actual.rdf against expected results
On RDF/XML Syntax
Too constrained for some
Tries to look like Book/author/title metadata but has subtle
constraints with striping, rdf:about,rdf:resource, etc.
Not constrained enough for others
doesn't work with DTDs nor W3C XML Schemas; works awkwardly
with XPath and XSLT
At least the issues in the 1998 spec have all been resolved,
complete with test cases. There are plenty of interoperable
parsers. And it works great with Relax-NG and nxml-mode :)
Observation: lots of structured data in XHTML
dialects
bibliographies
schedules
issues lists
news items
blog rolls
Data in Documents
I believe that one of the best ways to transition into RDF,
if not a long-term deployment strategy for RDF, is to manage the
information in human-consumable form (XHTML) annotated with just
enough info to extract the RDF statements that the human info
is intended to convey. In other words: using a relational
database or some sort of native RDF data store, and spitting
out HTML dynamically, is a lot of infrastructure to operate
and probably not worth it for lots of interesting cases.
We all know that we have to produce a human-readable version
of the thing... why not use that as the primary source?
GRDDL: author explicitly agrees to data extraction algorithm
rel="transformation" is grounded in URI space: http://www.w3.org/2003/g/data-view#transformation
output of transformation is expressed in RDF, using URIs for
property names
A person (or a machine) can "follow your nose" from the document
to the transformation algorithm, to the data, to the definitions of
the terms used in the data.
GRDDL Syntax: author's choice
works with DTD-happy XHTML
via a link with rel="transformation",
qualified by the GRDDL profile
works with XML in general
via grdd:transformation attribute on the root element
the link refers to a transformation, typically XSLT, that maps
to RDF/XML
the link may be indirect via a profile or namespace document
GRDDL drawback: turing completeness
XSLT is a big hammer
much less so than in 2000
Trust issues: consumer runs XSLT from who knows where
well-known transformations should cover 80%
short-cut local implementation
known-good cached copies
GRDDL Details
In addition to structured XHTML, add the GRDDL profile and
a typed link:
<Book rdf:ID="book1">
<dc:title>The Grapes of Wrath</title>
</Book>
<!-- no, this does not follow -->
<xsd:simpleType name="myInteger">
<xsd:restriction base="xsd:integer">
<xsd:maxInclusive value="99999"/>
</xsd:restriction>
</xsd:simpleType>
*RDF/XML does have a
rdf:parseType="Collection" syntax, which
expands to a lisp style binary tree in the abstract syntax. This
erasure property works not on XML elements, but on RDF statements.
Merging hCalendar data
OWL identity reasoning
Premise
# one-to-many
foaf:mbox a owl:InverseFunctionalProperty.
:dan foaf:mbox <mailto:connolly@w3.org>.
:dan foaf:name "Dan Connolly".
:daniel foaf:mbox <mailto:connolly@w3.org>.
:daniel foaf:name "Daniel W. Connolly".
java -jar pellet.jar -inputFile ,mash.rdf -unsat
Input file: ,mash.rdf
OWL Species: Full
DL Expressivity: ALCHIF(D)
Consistent: No
Reason: There is an anonymous individual X, identified by
this path (file:...cal/mash/calbg#oct6
http://www.cyc.com/2004/06/04/cyc#temporallyIntersects X),
which has more than 1 values for property file:...cal/mash/calbg#_city
violating the cardinality restriction
Time: 8784 ms (Loading: 6485 Preprocessing: 0
Species Validation: 2202 Consistency: 96 )
