1. Web-Technology
Lecture 13

2. Pre-quiz Who knows what Semantic Web is?
Who knows what R, D and F stand for in RDF?
Who knows why will we mention Dublin today?
Who knows what owl has to do any of this?

3. Semantic Web

4. A Very General Motivation
Every language has its own syntax and semantics
Syntax is the study of grammar. It defines how to structure of a message
how to say something?
Semantic is the study of meaning. It defines how to interpret a message
how to understand what one says?
Syntax Semantic Different syntaxes can have the same semantics
x += y
x = x + y

5. What does it have to do with WebTech?
Both syntax and semantics help to communicate information
Web is the largest information system
The syntax of information on the Web is defined by…
Where is its Semantics?..
It does not have its own. By default, it did not need any.
WWW has been created to to be consumed by humans.
Humans read and write in natural languages
they understand the texts and the links
Computers - not so much
HTML

6. Can we make computers understand the Web?
The Semantic Web (2001) By Tim Berners-Lee, James Hendler and Ora Lassila
Not the first piece about the term, but the most influential
Main idea:
Information on the Web can be given meaning
This will allow computers (agents) to understand it and communicate to each other based on this information
This will allow automate many online activities by giving computers complex tasks and delegating step-by-step execution of this tasks to them
A kind of a distributed Artificial Intelligence
Where would an old Web go?
Nowhere. Semantic Web is not a substitute or an update, but an extension

7. How does one build Semantic Web
He does not… not alone
Building semantic technologies involves lots of work and knowledge
SW is an evolution, not a revolution
Yet, it involves:
Many public data sets…
…provided with metadata…
…values interlinked…
.. and elements defined by common ontologies…
…and represented using open W3C SW standards.

8. Semantic Web Technologies
Publisher
Title
With an example
Genre
Author

9. RDF RDF stands for RDF statements expressing knowledge are triples
Resource: pages, dogs, ideas...everything that can have a URI
Description: attributes, features, and relations of the resources
Framework: model, languages and syntaxes for these descriptions
RDF statements expressing knowledge are triples
every piece of knowledge is broken down into (subject : predicate : object)
e.g.: Jane-Eyre : has-an-author : Charlotte-Bronte
RDF is a graph model that links description of resources together into networks
Subjects and objects are nodes, predicates are links
has-a-publisher
has-an-author
Penguin books
Jane-Eyre
Charlotte-Bronte

10. RDF (cont.) Resources are identified by their URIs (IRIs)
Subject is an URI or a blank node
Predicate is an URI
Object is an URI, blank node or a literal
An RDF model has a unique namespaces
URIs can be represented relatedly to a name space where they are defined
=> dc:creator
RDF specification defines the rules for creating RDF graphs and datasets as well as the basic RDF vocabulary (revised in 2014)

11. RDF-Schema (RDFS) RDF-Schema: extends RDF with basic vocabulary
allows to define new properties (predicates) and classes (types of resources)
Provides basic means for defining and controlling the semantics of RDF models
rdf:type
rdfs:subClassOf
rdfs:subPropertyOf
rdfs:domain
rdfs:range
“Jane Eyre”
my:has-title
my:has-publisher
my:has-author
rdf:type
my:Book
rdf:type
rdfs:subClassOf
my:Person
my:CreativeWork

12. Standard RDF Vocabularies
DC and DCterms (Dublic Core) – cataloguing digital resources
FOAF (Friend Of A Friend) - linking people on the Web
vCard – information about people and organisations
geo – geographical information …
“Jane Eyre”
dc:title
dc:publisher
dc:creator
rdf:type
my:Book
rdf:type
rdfs:subClassOf
foaf:Person
my:CreativeWork

13. Ontologies
In Philosophy: “Ontology is the study of being or existence. It seeks to describe the basic categories and relationships existing in reality.”
In AI and CS: “Formal ontology is an explicit intentional specification of shared conceptualization”
In Semantic Web: “Web-ontology is a document that formally defines the relations among terms in sharable format”.

14. Ontologies eat Lion Antelope ? Crocodile Lion Crocodile subClassOf
Carnivore
Animal
eat
subClassOf
not
subClassOf
Herbivore
Plant
eat
Tree
subClassOf

15. Web Ontology Language (OWL)
OWL is the main language for ontologies on SW
It is built on top of RDF, RDF Schema and RFF/XML syntax
Helps to define:
Class and property hierarchies
Instances
Axioms / constraints
Based on formal description logic, which means:
proper OWL ontology does not have logical conflicts
Know knowledge can be safely derived through formal inference and querying the ontology

16. Criticism of Semantic Web
Practical feasibility
HTML is easy
Semantic Web is way to complicated
Censorship and privacy
Semantic layer of Web information makes it easier for governments to discover knowledge and control
Doubling output formats
Information has to be presented in regular and semantic way

17. The current state of the Web

18. The current state of Semantic Web

19. Linked Data Deployment

20. Ontological Agreement

21. RDF Links

22. Open Linked Data

23. HTML-embedded Data

24. Schema.org Work started in August 2010
Google, Yahoo!, Microsoft & then Yandex
Goals:
One vocabulary understood by all the search engines
Make it very easy for the webmaster
It is A vocabulary. Not The vocabulary.
Webmasters can use it together other vocabs
We might not understand the other vocabs. Others might

25. Principles Incremental Simplicity Simple things should be simple
Webmasters shouldn’t have to deal with N namespaces
Complex things should be possible
Advanced webmasters should be able to mix and match vocabularies
has to fit in with existing workflows
Incremental
Started simple ( ~ 100 categories at launch)
Applies to every area
Add complexity after adoption (now >1200 vocab items)
Go back and fill in the blanks
Collaboration
Partner with Authoring platforms (Drupal, Wordpress, Blogger, YouTube…)
Work with others to incorporate their vocabularies
Any syntax possible (Microformats, RDFa, JSON-LD, …)

26. Overall Adoption in 2015

27. Widely-used Classes

28. Adoption by E-Commerce Websites

29. Properties used to Describe Products

30. Adoption by Travel Websites

31. Properties used to Describe Hotels

32. Adoption by Job Portals

33. Properties used to Describe Job Postings

34. Cool Applications

35. Cool Applications

36. Post-quiz Who knows what Semantic Web is?
Who knows what R, D and F stand for in RDF?
Who knows why have we mentioned Dublin today?
Who knows what owl has to do any of this?