Knowledge Organization Knowledge Organization Knowledge Organization Knowledge Organization SystemsSystems

Rajendra AkerkarWNRI, Norway

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SKOSSKOSSKOSSKOS

a model and vocabulary that is used to ybridge the world of knowledge organization systems (KOS) and the g y ( )Semantic Web

understanding SKOS will enhance your g yunderstanding about ontology

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KOSKOSKOSKOS a set of elements, often structured and

controlled that can be used for describing controlled, that can be used for describing objects, indexing objects, browsing collections, etc. etc.

KOSs are commonly found in cultural heritage KOSs are commonly found in cultural heritage institutions such as libraries and museums.

They can also be used in other scientific areas, examples include biology and chemistry,p gy y

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KOS examplesKOS examplesKOS examplesKOS examples Taxonomy◦ referring to the classification of things or

concepts, as well the schemes underlying such a classification.

Thesaurus◦ Thesaurus can be understood as an extension

to taxonomy: allowing subjects to be arranged i hi h d i ddi i i dd h in a hierarchy and in addition, it adds the ability to allow other statements be made about the subjectsabout the subjects

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They can make search more robust (instead of simple k d t hi l t d d f l keywords matching, related words, for example, can also be considered).

They can help to build more intelligent browsing interfaces (following the hierarchical structure, and explore broader/narrower terms etc )explore broader/narrower terms, etc.).

They can help us to formally organize our knowledge for a given domain, therefore promote reuse of the knowledge, and also facilitate data interoperability.

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KOSs are used for knowledge gorganization, whilst ontologies are used for knowledge representation.g p

KOSs are semantically much less rigorous than ontologies, and no formal reasoning g , gcan be conducted by just having KOSs.◦ For example, ontologies can specify a is-a relationship, while in

thesauri, the hierarchical relation can represent anything from is-a to part-of, depending on the interpretations rooted from the domain and application.

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The Semantic relation is fairly weak. An ontology is a rich expression of semantic

relationsrelations While a term list, free or controlled, is a natural

arrangement of word forms.g

BUT there is a kind of semantic relation betweenhi hi l li d l i hi li h hhierarchical lists and relationship lists that theyare both considered Subject-based classification

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It is any form of content classification thatbj t b th bj t th b ty

groups objects by the subjects they are about.This can take many forms, and is generallycombined with other techniques in order tocreate a complete solution.create a complete solution.

Metadata is generally defined as "data aboutdata," which is of course a very broad definition.y

In content management and informationarchitecture, metadata generally means"information about objects" ("objects" here usedinformation about objects ( objects here usedas defined above), that is, information about adocument, an image, a reusable contentmodule, and so on.

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The relation between subject-based classification andThe relation between subject based classification andmetadata is that metadata properties or fields that directlydescribe what the objects are about by listing discretesubjects use a subject-based classification.j j

Note that there is a difference between describing theobjects being classified and describing the subjects usedobjects being classified and describing the subjects usedto classify these objects

Metadata describes objects One of the ways in which it Metadata describes objects. One of the ways in which itdoes that, is by connecting objects to the subjects they areabout.

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Controlled vocabulary it is a closed list of namedysubjects, which can be used for classification. Inlibrary science this is sometimes known as anindexing language. The constituents of a controlledg g gvocabulary are usually known as terms.

A t i ti l f ti l t A term is a particular name for a particular concept.(This is pretty much the same as the common-sense notion of akeyword).

Same concept may have multiple names, and alsothat the same term may name multiple concepts

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that the same term may name multiple concepts.

Taxonomy is a subject-based classification thaty jarranges the terms in the controlled vocabulary into ahierarchy without doing anything further, though inreal life you will find the term "taxonomy" applied toy y ppmore complex structures as well.

Wh i T f ? Why is Taxonomy for?The benefit of this approach is that it allows relatedterms to be grouped together and categorized inways that make it easier to find the correct term touse whether for searching or to describe an object.

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Taxonomy helps users by describing they p y gsubjects.

Metadata only relates objects to subjects,whereas here we have arranged the subjects ina hierarchy.a hierarchy.

So a taxonomy describes the subjects beingused for classification, but is not itself metadata;it can be used in metadata, however.

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In this diagram, the blue lines are the metadata,g , ,while the black lines that make up thetaxonomy is part of the subject-basedclassification scheme.

R. Akerkar 13Figure. Using the taxonomy in metadata

The distinction derives from the blue lines beingstatements about the paper, but the black linep p ,between "topic maps" and "knowledgerepresentation" is not a statement about thepaper; it's a statement about "topic maps". Onep p ; p pconsequence of this is that if we have anotherpaper about "topic maps" we do not need torepeat that "topic maps"p p pbelong under "knowledgerepresentation".

Figure. Using the taxonomy in metadata

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A number of important pieces of information about the concepts are not being captured in the above taxonomy as:

The fact that "XML Topic Maps" is synonymous with "XTM".The fact that XML Topic Maps is synonymous with XTM . The difference between "XTM" and "topic maps". (Many users

use these interchangeably, but they do not mean the same thing.)

The fact that "topic navigation maps" is synonymous with "topicThe fact that topic navigation maps is synonymous with topic maps", but should no longer be used.

The relationship between topic maps and subject-based classification and topic maps and the semantic web.

The relationship between XTM and XML and HyTM and SGML.

The similiarity between HyTM and XTM and their difference from TMQLXTM, and their difference from TMQLand TMCL, as well as the similarity between TMQL and XQuery.

R. Akerkar 15Figure . Using the taxonomy in metadata

Taxonomy as we defined it here cannot handleTaxonomy as we defined it here cannot handlethese problems, though it should be noted thatmany systems referred to as taxonomies tosome extent can, as they extend the basicmodel defined here.

Figure 2. Using the taxonomy in metadata

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TaxonomiesIn a taxonomy the means for subject description consist ofIn a taxonomy the means for subject description consist ofessentially one relationship: the broader/narrowerrelationship used to build the hierarchy. The set of termsbeing described is of course open, but the language used todescribe them is closed, since it consists only of a single

l ti hiy g

relationship. Thesauri

Thesauri extend this with the RT and UF/USE relationships,and the SN property, which allow them to better describeth t A i th l i l d i thi i ththe terms. Again the language is closed, since this is theentire vocabulary at disposal for describing the terms

OntologyIn fact, thesauri could in theory be considered ontologywhere there is only one type called "term" one propertywhere there is only one type, called "term", one property,called "scope note", and three relationships (BT/NT,USE/UF, and RT). In practice thesauri are not consideredontologies because their descriptive power is far too weak,precisely because of this limited vocabulary.

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p y y

What Is SKOS?What Is SKOS?What Is SKOS?What Is SKOS?

Simple knowledge organization systems,p g g y◦ is an RDF vocabulary for representing KOSs, such as

taxonomies, thesauri, classification schemes, and bj t h di li tsubject heading lists.

◦ can be published on the Web and they can be machine readable and exchanged between software gapplications.◦ SKOS is developed by W3C Semantic Web

D l W ki G (SWDWG) d h Development Working Group (SWDWG) and has an official Web site: http://www.w3.org/2004/02/skos/

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SKOSSKOSSKOSSKOS

It has become a W3C standard on 18 August 2009

Note that the URIs in SKOS vocabulary ote t at t e U s S OS vocabu a y all have the following lead strings:

http://www w3 org/2004/02/skos/core# http://www.w3.org/2004/02/skos/core# By convention, this URI prefix string is

associated with namespace prefix skos: associated with namespace prefix skos: and is typically used in different sterilization formats with the prefix skossterilization formats with the prefix skos.

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ExampleExampleExampleExample

SKOS Core Constructs

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