6. HTTP is pretty good for creating, retrieving,
updating and deleting resources on the web
Image by Paul Downey
http://www.flickr.com/photos/psd/421186578/
Monday, October 25, 2010
7. XML and JSON based formats are pretty
good for representing resources
Photo by Alex Waterhouse-Hayward
http://blog.alexwaterhousehayward.com/2007_11_14_archive.html
Monday, October 25, 2010
8. But, just because a resource is represented in XML or JSON doesn’t
mean you know how to parse it or what the data means
Monday, October 25, 2010
9. Enter RDF
• Resource Description Framework (RDF)
• Simple data model
• Resources identified by URI
• Resources have property values
• Property values can be literal values
• Or URI links to other resources
• Property value also known as triple
• Subject - resource (identified by URI)
• Predicate - property type (identified by URI)
• Object - value of property
• RDF data can be represented in XML, JSON and other formats
• If it’s an RDF representation then you know how to parse it or what the data means
Monday, October 25, 2010
11. Example
Blog entry in RDF / Turtle
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dcterms: <http://purl.org/dc/terms/> .
@prefix foaf: <http://http://xmlns.com/foaf/0.1/> .
@prefix oslc: <http://open-services.net/ns/core#> .
@prefix oslc_blog: <http://open-services.net/ns/bogus/blogs#> .
<http://example.com/blogs/entry/1>
rdf:type oslc_blog:Entry ;
dcterms:content "Anything dirty or dingy or dusty. n
Anything ragged or rotten or rusty." ;
dcterms:creator
[ rdf:type foaf:Person ;
foaf:name "Oscar T. Grouch"
] ;
dcterms:modified "2002-10-10T12:00:00-05:00" ;
dcterms:title "I love trash" .
URI of this resource http://example.com/blogs/entry/1
Monday, October 25, 2010
12. Example
Change Request in RDF / XML
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dcterms="http://purl.org/dc/terms/"
xmlns:oslc="http://open-services.net/ns/core#"
xmlns:oslc_cm="http://open-services.net/ns/cm#"
xmlns:ex="http://example.com/bugtracker">
<rdf:Description rdf:about="http://example.com/bugs/2314">
<rdf:type
rdf:resource="http://open-services.net/ns/cm#ChangeRequest" />
<dcterms:identifier> 00002314 </dcterms:identifier>
<oslc:shortTitle>Bug 2314</oslc:shortTitle>
<dcterms:title> Invalid installation instructions </dcterms:title>
<dcterms:type> Defect </dcterms:type>
<oslc:instanceShape
rdf:resource="http://example.com/shapes/defect" />
<dcterms:description>
Invalid installation instructions indicating
invalid patches to be applied.
</dcterms:description>
...
</rdf:RDF>
URI of this resource http://example.com/bugs/2314
Monday, October 25, 2010
13. Example
RDFa embedded in HTML
<div about="/alice/posts/trouble_with_bob"
xmlns:dc="http://purl.org/dc/elements/1.1/">
<h2 property="dc:title">The trouble with Bob</h2>
The trouble with Bob is that he takes much better photos than I do:
!
<div about="http://example.com/bob/photos/sunset.jpg">
<img src="http://example.com/bob/photos/sunset.jpg" />
<span property="dc:title">Beautiful Sunset</span>
by <span property="dc:creator">Bob</span>.
</div>
</div>
Monday, October 25, 2010
14. Linked Data
Tim Berners-Lee outlined four principles of Linked Data in
his Design Issues: Linked Data note, paraphrased along the
following lines:
1. Use URIs to identify things.
2. Use HTTP URIs so that these things can be referred to and
looked up ("dereferenced") by people and user agents.
3. Provide useful information about the thing when its URI is
dereferenced, using standard formats such as RDF/XML.
4. Include links to other, related URIs in the exposed data to
improve discovery of other related information on the Web.
Monday, October 25, 2010
15. Problems with RDF
• Representations
• RDF/XML is a nightmare of complexity
• RDF/JSON not really there yet
• Perceptions of complexity
• RDF/XML doesn’t help
• Weird terminology: blank nodes, triples and reification, etc.
• I need a triple-store and a SPARQL query engine?
• Slow adoption, has it crossed the chasm?
But... RDF is not RDF/XML,
you can use other formats
But... there are some JSON
representations out there
Yes, there is some learning
curve but the underlying data
model is simple: resources
with property values
You might need an RDF
parser but not a full stack of
RDF technology to benefit
Who knows? We’ll review
some evidence of
momentum later...
Monday, October 25, 2010
16. Linked Data momentum
Linked Data major
part of upcoming
Drupal 7 release
http://sf2010.drupal.org/conference/sessions/story-rdf-drupal7-and-what-it-means-web-large
Monday, October 25, 2010
17. Linked Data momentum
US government
using Linked Data to
provide access to
government data
Monday, October 25, 2010
18. Linked Data momentum
UK government
using Linked Data to
provide access to
government data
Monday, October 25, 2010
21. How to benefit
• Web site designers and operators
• Use RDFa to mark-up data in your web pages
• Benefits:
• Search engines can index your data more effectively
• Software can more easily parse and make sense of your data
Monday, October 25, 2010
22. How to benefit
• REST API developers
• Use RDF as the data model for your REST web services
• Define your resources in terms of RDF properties
• Provide RDF representations of your resources
• Benefits:
• You don’t have to invent a new data model or a new XML or JSON format
• You can use standard property types
• And common vocabulary means easier inter-op with other web apps
Monday, October 25, 2010
23. Learn more
• O’Reilly Programming the Semantic Web
• http://oreilly.com/catalog/9780596153823
• W3C Linked Data initiative
• http://esw.w3.org/LinkedData
• Tim Berners-Lee:The next web of open linked data
• http://www.youtube.com/watch?v=OM6XIICm_qo
• Tim Berners-Lee: Linked Data is Blooming:WhyYou Should Care
• http://www.readwriteweb.com/archives/
linked_data_is_blooming_why_you_should_care.php
Monday, October 25, 2010
