GRANT AGREEMENT: 601138 | SCHEME FP7 ICT 2011.4.3 Promoting and Enhancing Reuse of Information throughout the Content Lifecycle taking account of Evolving Semantics [Digital Preservation]

“This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no601138”.

DOMAIN SPECIFIC MODELLINGStratos Kontopoulos, Panos Mitzias (CERTH/ITI)

“... a formal, explicit specification of a shared conceptualization...” [Studer et al., 1998]

Upper ontology: A model of the common objects that are generally applicable across multiple knowledge domains. Domain ontology: A model of concepts that belong to a specific domain or part of the world.

What is an Ontology?

machine readable with

computational semantics

unambiguous concepts, properties,

functions, axioms definition

commonly accepted

consensual knowledge

abstract, simplified model

of a domain

[Studer et al., 1998] Studer, R., Benjamins, V.R. and Fensel, D. (1998), Knowledge engineering: Principles and methods. Data & Knowledge Engineering, Elsevier Ltd, Vol. 25, Issues 1-2, pp. 161-197

◦ Classes (concepts)Superclass/subclass

relationship◦ Properties (relationships)

Subject → Predicate → Object◦ Axioms, restrictions and

constraints◦ Individuals (instances)

OWL - the Web Ontology Language

Key Notions

Pros:◦Variety of existing tools for representation,

consistency checking, reasoning, risk assessment etc.

◦Great fit for model-driven DP → queries & rules.Cons:◦Not fully mature technologies yet.◦Significant expertise & effort needed.

Why PERICLES likes Ontologies?

PERICLES Models▶ LRM -

ontology for modelling linked resources

▶DEM – formalism for digital ecosystems

▶Domain ontologies

◦ Ontology editor developed by Stanford University

◦ Free and open-source◦ Version 4.3 will be used in the examples

◦ Current version: 5.1.0◦ Also available as a web application

Exercise 1 – Create an ontology for digital videos

Video

CodecContainer

container1

video1

codec1

hasCodechasContainer

hasDuration

video2

codec2

Integer(e.g. 120)

Tasks:1. Open Protégé.2. Create classes Video, Codec and Container.3. Create object properties hasCodec and

hasContainer.4. Create datatype property hasDuration.5. Create instances for each class (e.g. video1, codec1,

etc.).6. Set the duration for each video.7. Connect instances using object properties.

Exercise 1 – Create an Ontology for Digital Videos

◦Why start from scratch? There is almost always an available third-party ontology that provides a useful starting point for our own ontology.

◦What do I gain? ◦Save the effort and time.◦Use validated and well-established ontologies.◦Take advantage of others’ domain expertise.◦Interact with the tools that use other ontologies

Consider Reuse

◦What to reuse? ◦Domain-specific ontologies◦Upper-level ontologies◦Ontology libraries◦Other resources

◦How is it done? Let’s go to exercise 2!

Consider Reuse

Tasks:1.Open Protégé and create a new ontology.2.Import the Digital Video ontology design

pattern from http://mklab.iti.gr/pericles/DigitalVideo_ODP.owl

3.Add a subclass of DigitalVideo called AnimationVideo.

Exercise 2 – Extend an existing ontology

◦What is a reasoner? A piece of software able to infer logical consequences.

◦What does it do? ◦Derives implicit information from explicitly

asserted knowledge.◦Performs consistency checking and validates the

ontology schema and content.◦Known reasoners: HermiT, Pellet, FaCT++,

Drools

Reasoners

Tasks:1.Run HermiT reasoner and check the inferred

information for class AnimationVideo.2.Stop the reasoner.3.Create instances for classes AnimationVideo

and VideoStream (e.g. shrek and videostream1).

4.Connect these two instances with property hasAudioStream.

5.Run HermiT reasoner and check results.6.Stop the reasoner and try to correct the errors!

Exercise 3 – Perform reasoning

◦Common inconsistencies◦Incompatible domain and range definitions for

transitive, symmetric, or inverse properties.◦Cardinality properties◦Requirements on property values can conflict

with domain and range restrictions.◦Solution: Specialized software (e.g. OOPS! -

OntOlogy Pitfall Scanner!)

Validation

Tasks:1.Visit oops.linkeddata.es2.Scan the Digital Video ontology with URI

http://mklab.iti.gr/pericles/DigitalVideo_ODP.owl

3.Check inconsistencies

Exercise 4 – Validate the ontology

◦Linked Data: The concept of Semantic Web to create links between datasets.

◦DBpedia: ◦Linked Data source with structured information

from Wikipedia.◦Available for querying via SPARQL language.◦Allows interlinking of the DBpedia dataset with

other datasets on the web.

Data Interlinkage

Tasks:1.Locate the instance of Shrek that we created.2.Add the seeAlso annotation to

http://dbpedia.org/resource/Shrek

Exercise 5 – Link with DBPedia