An introduction to semantics, RDF, and RDFa, with links to examples.

1. The Semantic Web
A web that is not the Web
for North NJ UX Meetup
Bruce Esrig, 11 June 2009

2. Aspects of the Semantic Web
• What is the semantic web?
• What happens behind the scenes?
• Where can we see semantics in action?
• How does semantic technology help?
• How can I design some knowledge?
• How can I use semantics in Web sites?

3. Disclaimer
• There is lots of material about the semantic
web.
• You’ll hear the terminology and see some
examples.
• Each subject requires more investigation to
make sense in an actionable way.
• If you’re new to this, don’t expect to
understand it all the first time through.

4. What is semantics?
• The art of constructing formal answers to the
question: “How does this work, really?”
• A geek-fest

5. Semantics in the history of science
• Galileo: Who cares what we think it does? Let’s
look and see what it really does.
• Frege, Peirce, Russell, Whitehead, Hilbert,
Goedel: Math is formal, let’s formalize that.
Oh, wait a second, math is too hard.
• Church, Kleene, Turing, ..., Milner: Maybe we
can formalize some sensible sub-domains.

6. Semantics as a way to model the world
An ideal, intermediate layer
“Dog”
Map to semantic layer
Map to reality
a real dog

7. Semantics as a way to model the world
The concept of a dog
“Dog”
Dog friends-with
a real dog

8. Semantics as a way to model the world
Dogs as individuals
“Maggie” “Molly”
friends-with
Maggie Molly
friends-with
one real dog another real dog

9. What is semantics?
Semantics
1. (Profession) A discipline that constructs
artificial languages that mediate between the real
world and the languages ordinarily used for
communication.
2. (Knowledge representation) Any intermediate
language constructed for the purpose of
explaining the concepts and relationships from
the real world that appear in utterances in a
particular language used for communication.

10. What is the Semantic Web?
Semantic web
1. (Knowledge representation) The description of
concepts and relationships in particular
knowledge domains, and the URI-based links
among those concepts and relationships
2. (Web 3.0) The use of knowledge to enable
semantics-aware behavior on the web

11. What is semantics?
(Introducing FOAF)
Here is a statement written in ordinary text:
Jimmy Wales knows Angela Beesly
Let’s agree to think about it this way:
Jimmy Wales and Angela Beesly are each the
name of a Person.
The first Person knows the second Person.

12. What is semantics?
foaf:knows
foaf:Person foaf:Person
foaf:name foaf:name
Jimmy Wales Angela Beesly

13. What happens behind the scenes?
RDF triples:
<foaf:Person rdf:about=quot;#JWquot;>
<foaf:knows>
<foaf:Person rdf:ID=quot;AngelaBeeslyquot;> .
<foaf:Person rdf:about=”#JW”>
<foaf:name>
“Jimmy Wales” .
<foaf:Person rdf:ID=”AngelaBeesly”>
<foaf:name>
“Angela Beesly” .

14. What happens behind the scenes?
<rdf:RDF
xmlns:foaf=quot;http://xmlns.com/foaf/0.1/quot;
xmlns:rdf=quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#quot;
<foaf:Person rdf:about=quot;#JWquot;>
<foaf:name>Jimmy Wales</foaf:name>
<foaf:knows>
<foaf:Person>
<foaf:name>Angela Beesley</foaf:name>
<!-- Wikimedia Board of Trustees -->
</foaf:Person>
</foaf:knows>
</foaf:Person>
</rdf:RDF>
Example is from: http://en.wikipedia.org/wiki/FOAF_(software)

15. Where can we see semantic modeling in action?
Site Semantic Feature
Catalog site
Taxonomy of departments and offerings
http://www.landsend.com
Faceted search for items (by body type,
size, fit, fabric ...)
CSS classes for globalnav, leftnavigation,
banners and headings, product, swatches,
product name, price

16. Where can we see the semantic web in action?
Site Semantic Feature
SearchMonkey accepts uploads of page
Search site specification data behind the scenes.
http://www.yahoo.com For Wikipedia pages, TOC and first
image show up in search results.
Semi-automatic indexing of Wikipedia
Reference site articles (with help from DBpedia).
http://www.freebase.com Shows topic and related topics for various
properties.

17. How does semantic technology help?
• Enables sites to expose data indicating what
their content is about
• Enables sites to organize themselves around
what their content is about
• Enables users to access information according
to what it is about
• Enables users to establish profiles stating what
they care about
• Enables sites to offer content their users care
about

18. How can I design some knowledge?
As tags:
User contributed
• Let users tag topics (and fragments)
• Look at their tags and promote the useful ones
Curated
• Figure out what aspects of your topics are significant
• Make up tags for each significant aspect, ignoring
how the tags might relate to each other or group
together
• Tag the topics

19. How can I design some knowledge?
As structured data:
• Figure out who your individuals are. Be prepared to support
a topic or fragment for each individual.
• Figure out what the individuals have in common and
define groups that individuals can join.
• Link the individuals according to what groups they
have in common.
• If necessary, group the groups. Offer navigation by
group.
• Figure out what relationships the individuals (or groups) have
• Link from one topic to another using the relationships.

20. How can I use semantics in web sites?
Site Semantic Feature
RDFa standard example
Integrate semantic assertions into a web
http://www.w3.org/TR/xhtml-rdfa-
page.
primer/alice-example.html
Promotional video (Drupal)
Automatic indexing. Better search results
http://www.youtube.com/watch?
based on clues in the content.
v=r4WgTRIRoa0
Course reading lists (Plymouth)
http://lists.lib.plymouth.ac.uk/ Indicate relationships among texts.
lists/abf203.html
Code snippets (Creative
Commons) Declare significance of parts of the page.
http://wiki.creativecommons.org/ Highlight creative commons licenses.
RDFa
See “RDFa in the wild” for more
examples (in the future).

21. M
eet Semantic Alice
Alice Birpemswick
Email: alice@example.com
Phone: +1 617.555.7332
My buddies:
* Bob
* Eve
* Manu

22. M
eet Semantic Alice
<div class=quot;socialnetquot; typeof=quot;foaf:Personquot; about=quot;#mequot;>
<p property=quot;foaf:namequot;>Alice Birpemswick</p>
<p>My buddies:</p>
<ul rel=quot;foaf:knowsquot;>
<li typeof=quot;foaf:Personquot;>
<a href=quot;http://example.com/bobquot; rel=quot;foaf:homepagequot;
property=quot;foaf:namequot;>Bob</a></li>
<li typeof=quot;foaf:Personquot;>
<a href=quot;http://example.com/evequot; rel=quot;foaf:homepagequot;
property=quot;foaf:namequot;>Eve</a></li>
<li typeof=quot;foaf:Personquot;>
<a href=quot;http://example.com/manuquot; rel=quot;foaf:homepagequot;
property=quot;foaf:namequot;>Manu</a></li>
</ul></div>

23. Extra slides

24. What happens behind the scenes?
<rdf:RDF xmlns:foaf=quot;http://xmlns.com/foaf/0.1/quot;
xmlns:rdf=quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#quot;
xmlns:rdfs=quot;http://www.w3.org/2000/01/rdf-schema#quot;>
<foaf:Person rdf:about=quot;#JWquot;>
<foaf:name>Jimmy Wales</foaf:name>
<foaf:mbox rdf:resource=quot;mailto:jwales@bomis.comquot; />
<foaf:homepage rdf:resource=quot;http://www.jimmywales.com/quot; />
<foaf:nick>Jimbo</foaf:nick>
<foaf:depiction rdf:resource=quot;http://www.jimmywales.com/aus_img_small.jpgquot; />
<foaf:interest rdf:resource=quot;http://www.wikimedia.orgquot;
rdfs:label=quot;Wikipediaquot; />
<foaf:knows>
<foaf:Person>
<foaf:name>Angela Beesley</foaf:name>
<!-- Wikimedia Board of Trustees -->
</foaf:Person>
</foaf:knows>
</foaf:Person>
</rdf:RDF>