Web-Technology Lecture 13

Semantic Web

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?

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

What does it have to do with WebTech? Both syntax and semantics help 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 be consumed by humans. We read and write in a natural language we understand the texts and the purpose of properly placed links Computers - not so much HTML My Therapist told me "Write letters to the people who you hate and burn them later". I did that, feel much better now... But what should I do with the letters???

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, probably, 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

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 It requires: Many public data sets… …provided with metadata… …with values interlinked… .. and elements defined by common ontologies… …and represented using open standards

Semantic Web Technologies Publisher Title With an example Genre Author

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

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 RDF models have unique namespaces (URIs of the models themselves) URIs can be represented relatedly to a name space where they are defined http://purl.org/dc/elements/1.1/creator => dc:creator RDF specification defines the rules for creating RDF graphs and datasets as well as the basic RDF vocabulary (revised in 2014) https://www.w3.org/TR/rdf11-concepts/

RDF-Schema (RDFS) RDF-Schema: extends RDF 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 (possible subjects) rdfs:range (possible objects) “Jane Eyre” http://www.penguin.com/ my:has-title my:has-publisher http://www.gutenberg.org/files/1260/1260-h/1260-h.htm my:has-author rdf:type https://en.wikipedia.org/wiki/Charlotte_Bront%C3%AB my:Book rdf:type rdfs:subClassOf my:Person my:CreativeWork https://www.w3.org/TR/rdf-schema/

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” http://www.penguin.com/ dc:title dc:publisher http://www.gutenberg.org/files/1260/1260-h/1260-h.htm dc:creator rdf:type https://en.wikipedia.org/wiki/Charlotte_Bront%C3%AB my:Book rdf:type rdfs:subClassOf foaf:Person my:CreativeWork

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 relations among terms in a sharable format”.

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

Web Ontology Language (OWL) OWL(2) 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 New knowledge can be safely derived through formal inference and querying the ontology

Reasoning and Inference Lion OWL(RDF) models are knowledge bases Some knowledge is specified New knowledge can be inferred Do Lyons eat Antelopes? Do Lyons eat Crocodiles? Do Crocodiles eat Crocodiles? Do Lyons eat Trees? Do Antelopes eat Grass? Crocodile subClassOf subClassOf Antelope subClassOf Carnivore Animal eat subClassOf not subClassOf Herbivore Plant eat Tree subClassOf subClassOf Inference Engines Grass Description Logic Semantic Web Rule Language (SWRL) hasParent(?x1,?x2) ∧ hasBrother(?x2,?x3) ⇒ hasUncle(?x1,?x3)

Querying RDF models are data sets SPARQL - SPARQL Protocol and RDF Query Language retrieve and manipulate data from RDF models and data sets Similar in functionality to SQL PREFIX ex: http://example.com/countryData# SELECT ?capital ?country WHERE { ?x ex:cityname ?capital ; ex:isCapitalOf ?y . ?y ex:countryname ?country ; ex:isInContinent ex:Africa . }

Criticism of Semantic Web Practical feasibility HTML is easy Semantic Web is 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 a regular and a semantic way

The current state of Semantic Web

The current state of Semantic Web

Open Linked Data Big data is big Most of it exists is silos 18 mil. open data sets This is more than web-pages when Google was founded Most of it exists is silos Isolated databases What if all of it can be Shared Externalized Connected

DB Pedia Semantic snapshot of Wikipedia more than 3.5 million things represented almost 2 million are classified in a consistent ontology 2,7 mil. links to images and 6,3 mil. links to external web pages over 1 billion pieces of information (RDF triples)

Linked Data Deployment

Ontological Agreement

RDF Links

HTML-embedded Data

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 vocabularies We might not understand the other vocabularies. Others might

Principles Incremental effort 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 effort 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, …)

Overall Adoption in 2015

Widely-used Classes

Adoption by E-Commerce Websites

Properties used to Describe Products

Adoption by Travel Websites

Properties used to Describe Hotels

Adoption by Job Portals

Properties used to Describe Job Postings

Google’s Knowledge Graph Launched in 2012 Global network of entities (not words) associated data links between relevant entities enhanced with historical search data Rich search snippets Relevant links to explore Facilitates inquiry Google’s Knowledge Graph https://www.youtube.com/watch?v=mmQl6VGvX-c

Facebook’s Open Graph

Personal Assistants Siri’s knowledge is represented in a unified modeling system that combines ontologies, inference networks, pattern matching agents, dictionaries, and dialog models. ... Siri isn’t a source of data, so it doesn’t expose data using Semantic Web standards

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?