Ontology Jan Pettersen Nytun Knowledge Representation Part I, JPN, - - PowerPoint PPT Presentation

Knowledge Representation Part I Ontology

Jan Pettersen Nytun

Knowledge Representation Part I, JPN, UiA 1

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Outline

• Knowledge
• Reasoning / logical Consequence
• Ontology

– Ontology in philosophy – Ontology in computer science – Different types of ontologies

• Levels of ontological precision

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Knowledge facts/understanding about a particular subject Representation a symbol or thing which represents something else (refers to, stands for)

is is

when we can not use the “original”, like things in the natural world or concepts

when to use

computer-understandable form

AI require

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Knowledge Representation (KR) is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge.

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From Wikipedia, the free encyclopedia (Knowledge representation and reasoning)

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Knowledge Base

• A database for knowledge management
• It provides means for information to be:

– Collected – Organized – Shared, searched and utilized (new information may be inferred)

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Knowledge Engineering

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• Get knowledge about some subject and

represent it in a computable form for some purpose.

• The knowledge engineer tells the system

what is true.

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Outline

• Knowledge
• Reasoning / logical Consequence
• Ontology

– Ontology in philosophy – Ontology in computer science – Different types of ontologies

• Levels of ontological precision

Knowledge Representation Part I, JPN, UiA 7

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Knowledge Base

Asserted and Inferred Statements

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The system knows how to infer new facts and solutions – the user may form questions and then the system gives answers.

Asserted Statements Inferred Statements Asserted Statements Inferred Statements

Inferred statements comes as a logical consequence of the asserted statements and logical rules

Entailment

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Knowledge Base

Entailment (Logical Consequence) Example: Family Information

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• Identify “something” as being Person:

Person(Ola), Person(Kari), Person(Marie), Person(Jan), …

• Gender of person:

Female(Kari), Male(Ola), Female(Marie), Male(Jan), …

• Who is parent to a person:

Parent(Ola, Marie), Parent(Kari, Marie), …

Inferred Statements Asserted Statements:

Person(Ola), Person(Kari), Person(Marie),Person(Jan), Female(Kari), …

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Knowledge Base

Example: Family Information … Continues

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Given the right logical rules, then family relations can be derived:

• Parent(x, y) and Female(x)  Mother(x, y)
• ??  Daughter (x, y)
• ??  Brother(x, y)

Asserted Statements:

Person(Ola), Person(Kari), Person(Marie),Person(Jan), Female(Kari), Male(Ola), Female(Marie), Male(Jan), Parent(Ola, Marie), Parent(Kari, Marie), …

Inferred Statements:

Mother(Kari, Marie), …

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Complex relations:

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Outline

• Knowledge
• Reasoning / logical Consequence
• Ontology

– Ontology in philosophy – Ontology in computer science – Different types of ontologies

• Levels of ontological precision

Knowledge Representation Part I, JPN, UiA 12

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What is an Ontology in Regard to Philosophy?

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From Wikipedia, the free encyclopedia

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Smith [1] the essence of

• ntology:

“provide a definitive and exhaustive classification

• f entities in all spheres
• f being.”

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What is an Ontology in Regard to Philosophy? Continues…

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What is an Ontology in Computer Science?

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Knowledge represented in a formal way:

• a hierarchy of concepts within a domain,
• a shared vocabulary to denote the types,
• properties and interrelationships of those

concepts.

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What is an Ontology in Computer Science? … Continues

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An ontology is a specification of a conceptualization that is designed for reuse across multiple applications and

• implementations. …a specification of a conceptualization

is a written, formal description of a set of concepts and relationships in a domain of interest. Peter Karp (2000) Bioinformatics 16:269

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Ontology vs Knowledge Base" “The Artificial-Intelligence literature contains many definitions of an ontology; many of these contradict

• ne another. … An ontology together with a set of

individual instances of classes constitutes a knowledge base. In reality, there is a fine line where the ontology ends and the knowledge base begins.”

[http://protege.stanford.edu/publications/ontology_development/ontology101-noy-mcguinness.html]

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Not All Would Agree On The Following:

• “An ontology is, very roughly, a formal representation of

a domain of knowledge. It is an abstract entity: it defines the vocabulary for a domain and the relations between concepts, but an ontology says nothing about how that knowledge is stored (as physical file, in a database, or in some other form), or indeed how the knowledge can be accessed.

• A knowledge base is a physical artifact: it is a database, a

repository of information that can be accessed and manipulated in some predefined fashion. The knowledge in a knowledge base can be said to be modeled according to an ontology.”

[http://answers.semanticweb.com/questions/21500/what-is-the-difference-between-knowledge-base-and-ontology]

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In computer science and information science, an ontology is… a practical application of philosophical ontology.

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[Ref. Medical Informatics: Knowledge Management and Data Mining in Biomedicine]:

From Wikipedia, the free encyclopedia:

Types of Ontologies

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Types of Ontologies… Continues

An upper ontology - also called top-level

• ntology or foundation ontology - describes the

most general concepts that are the same across all knowledge domains (e.g., Entity).

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Types of Ontologies… Continues

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General ontologies represent

knowledge at an intermediate level of detail independently of a specific task… theories of time and space, for example...

[Ref. Medical Informatics: Knowledge Management and Data Mining in Biomedicine]:

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Types of Ontologies… Continues

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Domain ontologies represent knowledge about a particular part of the world, such as medicine, and should reflect the underlying reality through a theory of the domain represented.

[Ref. Medical Informatics: Knowledge Management and Data Mining in Biomedicine]:

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Types of Ontologies… Continues

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…ontologies designed for specific tasks are called application ontologies. Conversely, reference

• ntologies are developed independently of any

particular purpose…

[Ref. Medical Informatics: Knowledge Management and Data Mining in Biomedicine]:

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Descriptive Ontology for Linguistic and Cognitive Engineering

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Outline

• Knowledge
• Reasoning / logical Consequence
• Ontology

– Ontology in philosophy – Ontology in computer science – Different types of ontologies

• Levels of ontological precision

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Catalog: A list of things.

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A Glossary, also known as a vocabulary,… is an alphabetical list of terms in a

particular domain of knowledge with the definitions for those terms.

From Wikipidia:

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A Taxonomy – also called a class hierarchy - organizes its data into

categories and subcategories.

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From Wikipidia: In general usage, a thesaurus is a reference work that lists words

grouped together according to similarity of meaning (containing synonyms and sometimes antonyms).

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From Wikipidia: A database schema …is a structure described in a formal

language… and refers to the organization of data as a blueprint of how a database is constructed (e.g., database tables for Relational Databases).

From Wikipidia: In mathematics, an axiomatic system is any set of

axioms from which some or all axioms can be used in conjunction to logically derive theorems. A mathematical theory consists of an axiomatic system and all its derived theorems.

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Ontology Engineering as a Discipline Studies the methods and methodologies for building

• ntologies.

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Reuse? Enumerate Terms Define Classes

Define Properties

Define Constraints Create Instances Decide Scope

Example of Process

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References

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[1] Book: David Poole and Alan Mackworth, Artificial Intelligence: Foundations of Computational Agents, Cambridge University Press, 2010, http://artint.info/ Sowa, John F. (2000) Knowledge Representation: Logical, Philosophical, and Computational Foundations, Brooks/Cole Publishing Co., Pacific Grove, CA. Artificial Intelligence: Structures and Strategies for Complex Problem Solving (Addison- Wesley), George F. Luger Smith Barry. Accessed 24th of March, 2013, Ontology: Philosophical and Computational. http: //ontology.buffalo.edu/smith/articles/ontologies.htm Quine WVO. On What There Is. Review of Metaphysics 1948;p. 21–38.

Knowledge Representation Part I, JPN, UiA