Knowledge organization systems (KOS)

Knowledge organization systems (KOS) is a general term referring to, among other things, the tools that present the organized interpretation of knowledge structures. This meaning of the term correspond to "semantic tools". In a broader way KOS may be understood also as, for example, libraries, encyclopedias, disciplines and the social division of labor in society. 


Within research in digital libraries has the term KOS been used. Hodge (2000) writes: “The term knowledge organization systems as used in this report was coined by the Networked Knowledge Organization Systems Working Group at its initial meeting at the ACM Digital Libraries Õ98 Conference in Pittsburgh, Pennsylvania.”


“The term knowledge organization systems is intended to encompass all types of schemes for organizing information and promoting knowledge management. Knowledge organization systems include classification and categorization schemes that organize materials at a general level, subject headings that provide more detailed access, and authority files that control variant versions of key information such as geographic names and personal names. Knowledge organization systems also include highly structured vocabularies, such as thesauri, and less traditional schemes, such as semantic networks and ontologies. Because knowledge organization systems are mechanisms for organizing information, they are at the heart of every library, museum, and archive. “ (Hodge, 2000).


(Hodge, 2000) presents the following types of KOS recognizing that the list is not comprehensive: They are grouped into three general categories: term lists, which emphasize lists of terms often with definitions; classifications and categories, which emphasize the creation of subject sets; and relationship lists, which emphasize the connections between terms and concepts. What Hodge actually provides is a suggestion for a taxonomy of KOS:



Term Lists

Classifications and Categories

Relationship Lists

According to Hodge “KOSs have the following common characteristics that are critical to their use in organizing digital libraries.

The above listed examples may be said to represent KOS in a narrow meaning of that word. There are other kinds of KOS in this narrow understanding, which should also be considered:

First of all should bibliometric maps be included in the taxonomy because bibliometric knowledge organization has turned out to be an important research area that should be seen as one approach among others in KO.


KOS as defined by Hodge (2000) is only a subcategory of what can reasonably be termed KOS. KOS in the broader sense include:

KOS in the narrow sense defined by Hodge may also be termed semantic tools because they are essentially selections of concepts supplied with information about their semantic relations to other concepts and symbols.


One may discuss whether the kinds of KOS mentioned belong to the same field. Generally the list is not theoretically justified but just ad hoc. Encyclopedias are probably by many thought to belong to a different kind of tools governed by different principles compared to what has traditionally been studied in the field of KO. Eco (1984), however, argues that  there is no well-defined border between dictionaries and encyclopedias. The meaning of words cannot be defined in isolation from knowledge about the status of the subject field, to which they belong. If Eco is right this has implications for the theory of KO. The definition and classification of KOS is therefore connected to a theoretical clarification of approaches to knowledge organization.


The importance of a generic concept like KOS is that it inspire to consider common principles as well as principal differences. By considering, for example a bibliometric map as a kind of KOS we may ask: In what ways is it related to other kinds of KOS? In what ways does it differ from other kinds of KOS? In what ways does it perform supplementary functions?



Why is it important to consider such a generic term as "Knowledge organization systems" (KOS)?

The idea is that it is important to learn what such systems have in common and in what ways the different KOS differs from each other (corresponding to definition by species and genus (these terms are not just used about biological categories), i.e., describing first by a broader category, the genus, then distinguished from other items in that category by differentia. The differentiae of a species are the species' properties that other members of the genus do not have. In short, the genus is the broad category, the species is a type within that category, and the differentiae are the distinguishing characteristics of the species. (Even though this classic view of definition is being challenged by, for example, the so-called prototype theory, it still has important merits).


Such generic terms are about the expertise that you are supposed to acquire during your education within LIS. A person told me that she considered herself an expert on such KOS as, for example, thesauri, but not on, for example, encyclopedias. Such a statement expresses a view about the relation of different kinds of KOS and might imply that this generic concept is a bad one or too broadly defined here (or as now done, consider semantic tools a sub-category of KOS).


So, a question is, are the methods, that are useful for constructing thesauri also useful for constructing encyclopedias? A different theories and methodologies at play?  Generic concepts such as KOS is supposed to provide a general theory and general methodological principles. This is why generic concepts are important. Of course we should always keep our concepts open to revision and of course we should not just regard the similarities but also the differences. An academic course in Knowledge Organization should not, however, only teach some special kinds of KOS but should consider the general principles as far as possible. This is especially important in the digital environment where most knowledge organizing systems and processes have to be reconsidered.







Eco, U. (1984). Semiotics and the Philosophy of Language. Bloomington: Indiana University Press.


Hodge, G. (2000). Systems of Knowledge Organization for Digital libraries. Beyond traditional authority files. Washington, DC: the Council on Library and Information Resources.


Garshol, L M (2004) Metadata? Thesauri? Taxonomies? Topic maps! Making sense of it all. Journal of Information Science, 30 (4). 378-391. Available online at:


Gilchrist, A (2003). Thesauri, taxonomies and ontologies - an etymological note. Journal of Documentation 59(1), 7-18.


Gorman, M, (2000). From Card Catalogues to WebPACS: Celebrating Cataloguing in the 20th Century. A talk given at the Library of Congress Bicentennial Conference on Bibliographic Control for the New Millennium Washington, D.C., November 15th 2000.


Pidcock,  Woody (2003). What are the differences between a vocabulary, a taxonomy, a thesaurus, an ontology, and a meta-model? Retrieved 2008-02-29 from:


Tudhope, D. & Lykke Nielsen, M. (2006).  Introduction to special issue: Knowledge Organization Systems and Services. New Review of Hypermedia and Multimedia, 12(1), 3-9.

Zeng, M. L. & Chan, L. M. (2004). Trends and issues in establishing interoperability among knowledge organization systems. Journal for the American Society for Information Science and Technology, 55(5), 377-395.


Åström, F (2002) Visualizing Library and Information Science concept spaces through keyword and citation based maps and clusters. In: Bruce, Fidel, Ingwersen & Vakkari (Eds). Emerging frameworks and methods: Proceedings of the fourth international conference on conceptions of Library and Information Science (CoLIS4), pp 185-197. Greenwood Village: Libraries unlimited. Two figures: Bibliometric_MAP_LIS.PDF; Bibliometric_LIS_2.PDF



See also: Semantic tool






Birger Hjørland

Last edited: 29-02-2008






1. Why is it important to consider different kinds of Knowledge Organizing Systems (KOS) from an overall (comparative) perspective?


2. What is the relevance of considering KOS in the broader sense of the term in relation to Library and Information Science? (i.e. in relation to the construction and use of KOS in the narrow sense = semantic tools).


3. What do all semantic tools have in common? What important issues are involved in the construction, use and evaluation of any semantic tool?


4. How do different kinds of KOS (understood narrowly as semantic tools) differ. Play The KOS Matching Game.


5. In what ways differ ontologies from more traditional forms of KOS/semantic tools such as thesauri?


6. Will some kinds of KOS/semantic tools become outdated by the development of more advanced forms?