Classification Systems

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......Classifica on Systems

Alberto Simõ[email protected]

March 14th, 2012

Alberto Simões Classifica on Systems

.. Classifica on Systems

Humans tend to organize;``disorganiza on is a kind of organiza on''This organiza on is usually done by classifica on;Classifica on can be as simple as tagging an object;``this is the pile of important documents, that of thenon-important ones''Classifica on is used everywhere!


.. Where are classifica on systems used?

Internet Social Networks (tagging);Libraries (universal decimal classifica on);Medicine (illness classifica on);Chemistry (periodic table);Geography (geographic taxonomy);Biology (protein classifica on);Linguis cs (languages classifica on);


.. Classifica on Systems Classes

Classifica on Systems can also be classified;One way to classify classifica on systems is by their ability toinclude proper es and rela ons between the classified objects;We will discuss four types of classifica on systems:

FolksonomiesTaxonomiesThesauriOntologies


.. Class Task

A B C

D E F


.. Folksonomies


.. Folksonomies

A folksonomy is a system of classifica on derived fromthe prac ce and method of collabora vely crea ng andmanaging tags to annotate and categorize content; thisprac ce is also known as collabora ve tagging, socialclassifica on, social indexing, and social tagging. Folk-sonomy, a term coined by Thomas Vander Wal, is a port-manteau of folk and taxonomy.

Folksonomy (Wikipedia, 2012)


.. Folsksonomies: How they work

The other classifica on techniques we will see, define someoneor some group in charge of crea ng the classifica on systemstructure (authority);This group of people see the world from a specific point of view,that can be, or not, shared by others;Folksonomies solve this problem: power to the people;Instead of par oning the world accordingly with a view, letsthe user present facets of objects;Users assign keywords (or tags, or labels) to objects (individuals);These keywords can be searched, indexed, and mathema calmodels can be applied to this data.


.. Folksonomies

An empirical analysis of the complex dynamics of tag-ging systems, published in 2007, has shown that consen-sus around stable distribu ons and shared vocabulariesdoes emerge, even in the absence of a central controlledvocabulary. For content to be searchable, it should becategorized and grouped. While this was believed torequire commonly agreed on sets of content describingtags (much like keywords of a journal ar cle), recent re-search has found that, in large folksonomies, commonstructures also emerge on the level of categoriza ons.Accordingly, it is possible to devise mathema cal mod-els that allow for transla ng from personal tag vocab-ularies (personomies) to the vocabulary shared by mostusers.

Folksonomy (Wikipedia, 2012)


.. Folksonomies: example

Top categories in the PT Wikipedia (those that don't have spaces):

375 Sociologia 383 Ponerinae395 Afro-brasileiros 404 Drilliidae413 Filosofia 415 Coleophoridae424 Psicologia 428 Terebridae445 Clathurellinae 445 Digimons445 Teuto-brasileiros 451 Apiaceae483 Asteroides 486 Luso-brasileiros492 Acaena 526 Rubiaceae537 Dolichoderinae 730 Agonoxenidae735 Acalypha 753 Mangeliinae762 Crambidae 787 Poaceae808 Coletâneas 824 Theraphosidae854 Myrmicinae 962 Fabaceae974 Formicidae 1065 Agrostis1096 Formicinae 1177 Aloe1328 Conus 1338 Ítalo-brasileiros1395 Asteraceae 1433 Coleophora1514 Arctiidae 1516 Alchemilla1689 Turridae 1879 Camponotus2163 Acer 2744 Acacia


.. Folksonomies: Pros and Cons

Pros:

doesn't require expert cataloguers, authorita ve sources orexpert users;capability of matching users' real needs and language:(inclusive --- includes everyone's words and vocabulary)controlled vocabularies are not prac cally and economicallyextensible;a low-investment bridge between personal classifica on andshared classifica on;easy to use and quick to classify big quan es of individuals;not all the limita ons of folksonomies are defects :-)


.. Folksonomies: Pros and Cons

Cons:

by itself, the vocabulary is flat;(there is no structure, just terms)not usable for small or few users collec ons;(sta s c methods significance is dependent on popula on size)without some technology help, vocabularies get inexact orambiguous;have a very low findability quo ent. They are great forserendipity and browsing but not aimed at a targeted approachor search;


.. Taxonomies


.. Taxonomies

Taxonomy is the science of iden fying and namingspecies, and arranging them into a classifica on. Thefield of taxonomy, some mes referred to as ``biologicaltaxonomy'', revolves around the descrip on and use oftaxonomic units, known as taxa. A resul ng taxonomyis a par cular classifica on, arranged in a hierarchicalstructure or classifica on scheme.

Taxonomy (Wikipedia, 2012)


.. Taxonomies

taxonomy [tækˈsɒnəmɪ]n.

(Life Sciences & Allied Applica ons / Biology)the branch of biology concerned with theclassifica on of organisms into groups based onsimilari es of structure, origin, etc.the prac ce of arranging organisms in this way.

the science or prac ce of classifica on.[from French taxonomie, from Greek taxis order + -nomy]

Collins English Dic onary – Complete and Unabridged© HarperCollins Publishers 1991, 1994, 1998, 2000, 2003


.. Taxonomies: How they work?

Used to par oning the world in disjunc ve classes or groups;Each group is, again, par oned in sub-classes or sub-groups;And sub-classes are par oned, and…

Individuals are classified in one leaf category;(a classifica on is a path in the tree)


.. Taxonomies: The typical example


.. Taxonomies: The example you use everyday

Main index (top level) of Universal Decimal Classifica on:

0 Generali es(now Science and knowledge. Organiza on. Computer Science.Informa on. Documenta on. Librarianship. Ins tu ons. Publica ons)

1 Philosophy. Psychology2 Religion. Theology3 Social Sciences4 Vacant5 Mathema cs and natural sciences6 Applied sciences. Medicine. Technology7 The arts. Recrea on. Entertainment. Sport8 Language. Linguis cs. Literature9 Geography. Biography. History


.. Taxonomies: The example you use everyday

8 Language. Linguis cs. Literature80 General ques ons […] linguis cs and literature. Philology81 Linguis cs and languages81-11 Schools and trends in linguis cs81-13 Methodology of linguis cs. Methods and means811 Languages811.1/.2 Indo-European Languages

811.3 Dead languages of unknown affilia on. Caucasian languages811.4 Afro-Asia c, Nilo-Saharan, Congo-Kordofanian, Khoisan languages811.5 Ural-Altaic, Palaeo-Siberian, Eskimo-Aleut, Dravidian and

Sino-Tibetan languages. Japanese. Korean…811.6 Austro-Asia c languages. Austronesian languages811.7 Indo-Pacific (non-Austronesian) languages. Australian languages811.8 American indigenous languages811.9 Ar ficial languages

82 Literature


.. Taxonomies: Class Task

0 Science and knowledge. Organiza on.Computer Science. Informa on…

1 Philosophy. Psychology

2 Religion. Theology

3 Social Sciences

5 Mathema cs and natural sciences

6 Applied sciences. Medicine. Technology

7 The arts. Recrea on. Entertainment.Sport

8 Language. Linguis cs. Literature

9 Geography. Biography. History Prolog Programming forAr ficial Intelligence,Prof Ivan Bratko


.. Taxonomies: Class Task5 Mathema cs, Natural Sciences51 Mathema cs

519 (no name, virtual class)519.6 Computa onal mathema cs.

Numerical Analysis

SDUM

Prolog Programming forAr ficial Intelligence,Prof Ivan Bratko



0 Science and knowledge. Organiza on.Computer Science. Informa on…00 Prolegomena. Fundamentals of

knowledge and culture.Propaedeu cs004 Computer science and technology.

Compu ng. Data processing004.4 So ware

004.42 Computer programming.Computer programs

UAProlog Programming forAr ficial Intelligence,Prof Ivan Bratko





Compu ng. Data processing004.4 So ware

004.43 Computer Languages

IPP






Compu ng. Data processing004.8 Ar ficial intelligence

UAlg



.. Taxonomies: Pros and Cons

Pros:

rigid tree, makes it easy to process;suitable for some areas (like life classifica on);the hierarchy helps searching for terms (abstrac on);

Cons:

rigid tree, makes it difficult to classify;(different people classify objects differently)the structure is defined by some authority group;(for example, the UDC Consor um)forces the subdivision of the world;(categories are single-parental)as a workaround, people classify in more than one category;(so, the rigid tree Pro gets a Con)


.. Thesauri


.. Thesauri

A thesaurus is a reference work that lists words groupedtogether according to similarity of meaning (contain-ing synonyms and some mes antonyms), in contrast toa dic onary, which contains defini ons and pronuncia-ons.

Thesauri (Wikipedia, 2012)


.. Thesauri

In Informa on Science, Library Science, and Informa onTechnology, specialized thesauri are designed for infor-ma on retrieval. They are a type of controlled vocabu-lary, for indexing or tagging purposes. Such a thesauruscan be used as the basis of an index for online material.[…]Unlike a literary thesaurus, these specialized thesauritypically focus on one discipline, subject or field of study.



.. Thesauri: How they work!

Thesauri for informa on retrieval are typically con-structed by informa on specialists, and have their ownunique vocabulary defining different kinds of terms andrela onships.

Terms are the basic seman c units for conveying con-cepts. They are usually single-word nouns, since nounsare the most concrete part of speech. […] When a termis ambiguous, a ``scope note'' can be added to ensureconsistency, and give direc on on how to interpret theterm.

``Term rela onships'' are links between terms. These re-la onships can be divided into three types: hierarchical,equivalency or associa ve.

Thesauri (Wikipedia, 2012)Alberto Simões Classifica on Systems


Hierarchical rela onships are used to indicate termswhich are narrower and broader in scope. A ``BroaderTerm'' (BT) or hyperonym is a more general term. Recip-rocally, a ``Narrower Term'' (NT) or hyponym is a morespecific term.BT and NT are reciprocals; a broader term necessarilyimplies at least one other term which is narrower. BTand NT are used to indicate class rela onships, as wellas part-whole rela onships (meronyms and holonyms).




Example of a thesaurus with hierarchical rela ons.

Feline

NT Cat

NT Panther

Cat

BT Feline

Panther

BT Feline

NT Pink Panther

Pink Panther

BT Panther



The equivalency rela onship is used primarily to con-nect synonyms and near-synonyms. `Ùse'' (USE) and`Ùsed For'' (UF) indicators are used when an autho-rized term is to be used for another, unauthorized,term. Unauthorized terms are o en called `èntry vo-cabulary'', `èntry points'', ``lead-in terms'', or ``non-preferred terms'', poin ng to the authorized term (alsoreferred to as the ``preferred term'' or ``descriptor'') thathas been chosen to stand for the concept.




Example of a thesaurus with equivalency rela ons.

Parliament

USE European Parliament

Parliament of Europe

USE European Parliament

European Parliament

UF Parliament

UF Parliament of Europe



Associa ve rela onships are used to connect two re-lated terms whose rela onship is neither hierarchicalnor equivalent. This rela onship is described by the in-dicator ``Related Term'' (RT). Associa ve rela onshipsshould be appliedwith cau on, since excessive use of RTswill reduce specificity in searches.Consider the following: if the typical user is searchingwith term "A", would they also want resources taggedwith term "B"? If the answer is no, then an associa verela onship should not be established.




Example of a thesaurus with associa ve rela ons.

Douro Porto

BT River BT Portugal

RT Porto

RT Gaia Portugal

NT Porto

River NT Gaia

NT Douro

City

Gaia NT Gaia

BT Portugal NT Porto

Note RT is not symmetrical. a RT b ̸⇒ b RT a.


.. Thesauri: a simple example

Quality Asia

ChinaFood Safety Contamination

Food Food Contamination

BT

NT

BT

NT

RT RT

USE

USE

Extract of Food Safety relationships in AGROVOC


.. Thesauri: Pros and Cons

Pros:

More flexible than Taxonomies;(does not require a tree, work as a graph)Have other types of rela onship than simple hierarchy;There is an ISO standard that documents their correct use;Standard defines mathema cal proper es for rela onships;

Cons:

Standardized types of rela onship are kind of limited;(same rela on for hyperonyms and meronyms)(non-hierarchical rela on is too vague: related)No support for rela onships with non-terms (features);


.. Ontologies


.. Ontologies

Ontology is the philosophical study of the nature of be-ing, existence, or reality as such, as well as the basic cat-egories of being and their rela ons. Tradi onally listedas a part of the major branch of philosophy known asmetaphysics, ontology deals with ques ons concerningwhat en es exist or can be said to exist, and how suchen es can be grouped, related within a hierarchy, andsubdivided according to similari es and differences.

Ontology (Wikipedia, 2012)


.. Ontologies

In computer science and informa on science, an ontol-ogy formally represents knowledge as a set of conceptswithin a domain, and the rela onships between thoseconcepts. It can be used to reason about the en eswithin that domain and may be used to describe the do-main.

Ontology: informa on science (Wikipedia, 2012)


.. Ontologies

Contemporary ontologies share many structural simi-lari es, regardless of the language in which they areexpressed. Most ontologies describe individuals (in-stances), classes (concepts), a ributes, and rela ons.



.. Ontologies

Individuals are the instances or objects (the basic or``ground level'' objects).


Unlike any of the other classifica on systems, Ontologies clearlyinclude the individuals (or objects being classified) in the structure.


.. Ontologies

Individuals are the instances or objects (the basic or``ground level'' objects).


Unlike any of the other classifica on systems, Ontologies clearlyinclude the individuals (or objects being classified) in the structure.


.. Ontologies

Classes are sets, collec ons, concepts, […] or kinds ofthings.


Classes are the concepts used in Thesauri and Taxonomy. They can besuper-classes, including sub-classes, or can just include individuals(low level classes, leafs if we were talking about taxonomies).


.. Ontologies

Classes are sets, collec ons, concepts, […] or kinds ofthings.


Classes are the concepts used in Thesauri and Taxonomy. They can besuper-classes, including sub-classes, or can just include individuals(low level classes, leafs if we were talking about taxonomies).


.. Ontologies

A ributes are aspects, proper es, features, characteris-cs, or parameters that objects (and classes) can have.


A ributes are proper es of individuals or classes. If the individual is abook on a library, a property can be the number of pages, the tle,the author. For a class, like ``mammal'', an a ribute can be areference to its fur.


.. Ontologies

A ributes are aspects, proper es, features, characteris-cs, or parameters that objects (and classes) can have.


A ributes are proper es of individuals or classes. If the individual is abook on a library, a property can be the number of pages, the tle,the author. For a class, like ``mammal'', an a ribute can be areference to its fur.


.. Ontologies

Rela ons are ways in which classes and individuals canbe related to one another.


Rela ons are similar to the rela ons used in Thesauri, but unlikethem, there isn't a list of valid rela ons. They can be the commonhierarchical rela ons, or the rela on `èat'' rela ng animals with theanimals they eat.


.. Ontologies

Rela ons are ways in which classes and individuals canbe related to one another.


Rela ons are similar to the rela ons used in Thesauri, but unlikethem, there isn't a list of valid rela ons. They can be the commonhierarchical rela ons, or the rela on `èat'' rela ng animals with theanimals they eat.


.. Ontologies

Func on terms: complex structures formed from certainrela ons that can be used in place of an individual termin a statement.


Suppose you are adding Portuguese rivers to an Ontology. One candefine a simple macro to add some default rela ons to the river:

River(name)∼=

Term → nameIs a → riverIs at → Portugal


.. Ontologies

Func on terms: complex structures formed from certainrela ons that can be used in place of an individual termin a statement.


Suppose you are adding Portuguese rivers to an Ontology. One candefine a simple macro to add some default rela ons to the river:

River(name)∼=

Term → nameIs a → riverIs at → Portugal


.. Ontologies

Restric ons: formally stated descrip ons of what mustbe true in order for some asser on to be accepted as in-put.


We can force that a capital of a country it a city:

add (X capital-of Y) iff X is-a City


.. Ontologies

Restric ons: formally stated descrip ons of what mustbe true in order for some asser on to be accepted as in-put.


We can force that a capital of a country it a city:

add (X capital-of Y) iff X is-a City


.. Ontologies

Rules: statements in the form of an antecedent-consequent sentence that describe the logical inferencesthat can be drawn froman asser on in a par cular form.


In the other hand, if we trust who is edi ng an ontology, we canclassify automa cally it as a city, and its country as a…country:

X capital-of Y⇒X is-a City ∧ Y is-a Country


.. Ontologies

Rules: statements in the form of an antecedent-consequent sentence that describe the logical inferencesthat can be drawn froman asser on in a par cular form.


In the other hand, if we trust who is edi ng an ontology, we canclassify automa cally it as a city, and its country as a…country:

X capital-of Y⇒X is-a City ∧ Y is-a Country


.. Ontologies

Axioms: asser ons (including rules) in a logical form thattogether comprise the overall theory that the ontologydescribes in its domain of applica on.


Differs from Rules in the aspect as axioms are tests to guarantee theontology structure. They are not used to infer new rela ons. Theyassert.


.. Ontologies

Axioms: asser ons (including rules) in a logical form thattogether comprise the overall theory that the ontologydescribes in its domain of applica on.


Differs from Rules in the aspect as axioms are tests to guarantee theontology structure. They are not used to infer new rela ons. Theyassert.


.. Ontologies

Events: the changing of a ributes or rela ons.


Similar to rules, but react to events. For example, if the user adds afeature sta ng that an individual lays eggs, classify it as an oviparous.

Note that the division in Rules, Axioms and Events is not universal,and depend quite a lot in the applica on that is used to support theontology.


.. Ontologies

Events: the changing of a ributes or rela ons.


Similar to rules, but react to events. For example, if the user adds afeature sta ng that an individual lays eggs, classify it as an oviparous.

Note that the division in Rules, Axioms and Events is not universal,and depend quite a lot in the applica on that is used to support theontology.


.. Ontologies: Example 1


.. Ontologies: Example 2


.. Ontologies: Pros and Cons

Pros:

More flexible than Thesauri;(graph with ad-hoc rela onships)Lots of formalisms and standards (OWL, SKOS, …);Lots of tools to edit (like Protégé);Languages for querying and comple on (like SPARQL);

Cons:

As a classifica on approach, requires an authority for itsdefini on, just like Taxonomies or Thesauri.Complexity: not everybody is able to create a detailed ontology.


.. Further Reading

Folksonomies:

Folksonomy Coinage and Defini onhttp://vanderwal.net/folksonomy.html

Folksonomies: A User-Driven Approach to Organizing Contenthttp://www.uie.com/articles/folksonomies/

Folksonomies: power to the peoplehttp://www.iskoi.org/doc/folksonomies.htm

Folksonomies: Tidying up Tags?http://www.dlib.org/dlib/january06/guy/01guy.html

Folksonomies - Coopera ve Classifica on and Communica onThrough Shared Metadatahttp://www.adammathes.com/academic/

computer-mediated-communication/folksonomies.html


http://vanderwal.net/folksonomy.html

http://www.uie.com/articles/folksonomies/

http://www.iskoi.org/doc/folksonomies.htm

http://www.dlib.org/dlib/january06/guy/01guy.html

http://www.adammathes.com/academic/computer-mediated-communication/folksonomies.html

http://www.adammathes.com/academic/computer-mediated-communication/folksonomies.html

.. Further Reading

Taxonomies:

Taxonomyhttp://en.wikipedia.org/wiki/Taxonomy

Perspec ves on Taxonomy, Classifica on, Structure andFind-abilityhttp://www.serviceinnovation.org/included/docs/

kcs_taxonomy.pdf

Universal Decimal Classifica onhttp://www.udcc.org/udcsummary/php/index.php

Thesauri:

Thesaurushttp://en.wikipedia.org/wiki/Thesaurus

Thesaurus principles and prac cehttp://www.willpowerinfo.co.uk/thesprin.htm


http://en.wikipedia.org/wiki/Taxonomy

http://www.serviceinnovation.org/included/docs/kcs_taxonomy.pdf

http://www.serviceinnovation.org/included/docs/kcs_taxonomy.pdf

http://www.udcc.org/udcsummary/php/index.php

http://en.wikipedia.org/wiki/Thesaurus

http://www.willpowerinfo.co.uk/thesprin.htm

.. Further Reading

Ontologies:

Ontology (informa on science)http://en.wikipedia.org/wiki/Ontology_

(information_science)

Protégé Ontology Editorhttp://protege.stanford.edu/

OWL Web Ontology Languagehttp://www.w3.org/TR/owl-features/

SPARQL Query Language for RDFhttp://www.w3.org/TR/rdf-sparql-query/


http://en.wikipedia.org/wiki/Ontology_(information_science)

http://en.wikipedia.org/wiki/Ontology_(information_science)

http://protege.stanford.edu/

http://www.w3.org/TR/owl-features/

http://www.w3.org/TR/rdf-sparql-query/

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Classification Systems

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