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]

Semantic Web & Ontologies Panos Mitzias (CERTH/ITI)

◦The case: Global information cannot be utilized efficiently. We need to search, select, read/listen/watch, combine, use, create, publish vast amounts of information.◦The problem: Computers do not understand meaning!

◦The Semantic Web vision:“The idea of having data on the web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications.”

[www.w3.org/ECommerce]

The Semantic Web

"The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers & people to work in cooperation."

[Tim Berners-Lee]

The Semantic Web

https://en.wikipedia.org/wiki/Semantic_Web_Stack

By enabling/facilitating:◦the expression of data and their meaning

metadata standards (for universal approach)

◦the simpler, automatic processing of data◦broader connections between similar sources of data◦enhanced reasoning◦better access, searching, etc.

How does Semantic Web help?

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

◦Upper-level 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

◦Analysis and formalization of the domain knowledge.

◦Semantic representation/interpretation of information.

◦Sharing common understanding of the structure of information.

◦Reuse of domain knowledge.

◦Reasoning to infer new information.

◦Ensure consistency of the domain representation.

Why are Ontologies Useful?

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 technology yet.◦Significant expertise and effort needed.

Why PERICLES likes Ontologies?

Thank you!