Proceedings of the Tenth International Conference on Conceptions of Library and Information Science, Ljubljana, Slovenia, June 16-19, 2019
Levels of information, and library and information science as a science of mentefacts
Introduction. This article recosiders some basic notions in library and information science, including those of work, knowledge organization system, information and library and information science itself, in light of the theory of levels of reality.
Method. This theory is briefly outlined, especially in its version by Nicolai Hartmann, which considers ideal being, matter, life, mind and spirit (culture) as major levels, and analyzes spirit into personal spirit, objective (social) spirit and objectivated (intellectual) spirit. Objectivated spirit has been further analyzed into artefacts and mentefacts in Gnoli (2018).
Analysis and results. Mentefacts is a notion of special relevance to library and information science. As suggested by commenters, works are mentefacts, although not the only type of them. For example, knowledge organization systems are also mentefacts, and should therefore be studied in all their three levels of personal, objective and objectivated spirit. Information as conceived by Floridi is a fundamental entity pertaining to all levels, rather than only to the level of mentefacts which is the focus of library and information science.
Conclusions. This suggests that theoretical foundations of library and information science should not rely exclusively on Floridi’s philosophy of information, but more on notions specific to the level of mentefacts, such as those of concept, argument, work, citation, bibliographic family, subject, knowledge organization system etc. To be distinguished from other disciplines, library and information science should be conceived as a science of mentefacts.
Levels of reality as represented in knowledge organization and library and information science
The theory of levels of reality (Poli, 2001) is an important philosophical reference in knowledge organization, which has inspired in more or less explicit ways classification structures as viewed by J.D. Brown, E.C. Richardson, H.E. Bliss, the Classification Research Group, I. Dahlberg and others (Kleineberg, 2017); the recent Integrative Levels Classification project takes its very name from it (Gnoli, 2017).
The theory formalizes an idea quite common in philosophy of science, that can be tracked back to at least Auguste Comte and Friedrich Engels: that a series of levels of organization can be identified in reality, each depending on lower levels for its existence, but also showing its own original properties that cannot be reduced to them. For example, the level of life depends on the lower level of matter, as living beings are formed with material atoms and molecules, but has such novel properties as metabolism, growth and death that make no sense at the level of matter itself. Major levels can in turn be analyzed into minor ones: for example, life includes the minor levels of genes, cells, organisms and natural populations.
The version most known in library and information science literature is the "theory of integrative levels", proposed by the biochemist Joseph Needham and formalized by the psychologist James K. Feibleman (1954), which has been received by the CRG within a scientifically-oriented milieu (see references in Gnoli, 2017 and in Kleineberg, 2017). By its application, natural phenomena can be arranged in a series of levels including particles, atoms, molecules, cells, organisms, populations, and societies.
Critical comments have argued that the theory would not be suitable to arrange human-related knowledge, such as social sciences and the humanities. However, an evolutionary ontology structured into levels can also be found in thinkers belonging to traditions very different from scientific materialism, like Pierre Teilhard de Chardin, a geologist and a priest. The most advanced study of levels of reality has been developed within the refoundation of modern philosophical ontology by Baltic German philosopher Nicolai Hartmann (Riga 1882-Göttingen 1950), whose relevance is recently being rediscovered through translations of his works and a series of conferences.
Hartmann's levels include, besides a material, an organic and a psychic level (called "strata" by him), also a further "spiritual" stratum which accounts for all the complex phenomena of human culture (Hartmann, 1940). Along with these strata that form "the real being", Hartmann also considers "the ideal being" covering such abstract entities as values, logic and mathematical structures, which in some writings he considers as a kind of pre-material foundational level:
The being stratum of physical matter, of spatial motion, of mechanism and of energy is not the lowest stratum. Further below, the realm of quantitative constitutes a lower and more elementary stratum; as such, it is not reality yet, but an inferior type of being -- so to speak unfulfilled -- an only ideal being, only essence without existence (Hartmann, 1931, section 15).
This level seems to be suitable to include the more recent notion of information meant as a general, foundational entity, as advocated more recently in "it from bit" views (see Gnoli and Ridi, 2014), in structural realism (French, 2017) and in Luciano Floridi's philosophy of information (see section 4).
Hartmann's ontology is reflected in the main classes of Dahlberg's Information Coding Classification, which start indeed with a class of formal entities, followed by those of energy and matter, cosmos and Earth, organic entities, humans, societies, economies and technologies, science and information products, and cultures (Ohly, 2018). Again, this scheme of levels received in knowledge organization is not limited to natural phenomena but also covers cultural ones.
The core of knowledge organization is usually considered to be part of library and information science, although some broader aspects of knowledge organization also concern knowledge in education, in society and in culture generally, e.g. university curricula or encyclopedias (Hjørland, 2016, section 4); in turn, some technical aspects of library and information science concern information services and practices not necessarily involving knowledge organization: so that the relationship between knowledge organization and library and information science can be thought as one of intersection rather than inclusion.
In any case, an important question is whether the theory of levels of reality can be fruitfully extended from knowledge organization to the whole of library and information science. In a previous paper (Gnoli, 2018), I have started to discuss the application of Hartmann's highest level of "spirit", as well as Karl Popper's "World 3", to the theory of information science. Of special interest is Hartmann's analysis of this level into three components, that he calls personal spirit that is the cultural background of each individual human, objective spirit that is culture as shared socially in communities, and objectivated spirit that is cultural products.
I have compared objectivated spirit with the concepts of artefacts and mentefacts, meant as material products and intellectual products respectfully, as discussed in previous sociology and library and information science literature. (Personal spirit in turn has bio-psychological bases in the lower neural level, which should also be considered in an integrated approach to information seeking, cf. Bates, 2002.)
The resulting scheme of levels that have a potential interest for library and information science theory (ignoring finer subdivisions) is thus as follows:
- forms (including information in the fundamental sense)
- matter (incl. structural information)
- life (incl. genetic information)
- mind (incl. neural information)
- spirit = culture
- personal spirit (incl. memory, learning)
- objective (social) spirit (incl. language, symbols)
- objectivated spirit
- artefacts (incl. designed objects, information and communication technologies, documents)
- mentefacts (incl. artworks, intellectual works)
Notice that, following the gravitational metaphor of levels resting each upon the lower ones, the scheme could be written in the reversed order, with forms at the bottom and mentefacts at the top.
The rest of this paper will compare this scheme with some basic notions of library and information science, including those of work, knowledge organization system and information. This is intended to enhance the understanding of which levels of reality the objects of library and information science lie at, and as a consequence which is the most appropriate collocation of library and information science itself.
Mentefacts and works
Reacting to my previous paper, both Dousa (personal communication, June 22, 2018) and Hjørland (2018) have appropriately commented that mentefacts cover the important library and information science notion of work, which is not mentioned in that paper. These observations stimulate us to confront the notion of work against the framework of levels.
Work is discussed in depth by Smiraglia (2001) as a basic concept in library and information science, together with the related concepts of text and document. The author reviews previous definitions of works as separated from the documents that carry them by Lubetzky, Verona, Domanovsky, Wilson and others. After discussing aspects of works, he concludes that:
A work is the intellectual content of a bibliographic entity. A work functions in the society in the same manner that a sign functions in language. A work has the characteristics of a Peircean symbol. Works that are assumed in the canon of their cultures are likely to generate families of derivative mutations. A work that has become to mutate may become a collaborative phenomenon over time. Certain limited bibliographic characteristics of literatures... can be used to predict which works... have entered the canon... Substantial change in ideational or semantic content results in the creation of a new, but related, work (Smiraglia, 2001, p. 129).
From this it is clear that, although works interact with the level of objective spirit as they "function in the society" in certain ways, they also have their own life at the higher level of objectivated spirit: indeed, they can become part of a canon and stimulate the origin of new works, these being processes that happen independently from the origin of a work by a specific author and social milieu. Dante's Comedy has a canonical role in Italian literature beyond Dante's biography and late-Middle-Ages Florence environment that have stimulated its composition at the time. In turn, it is probably inspired by representations of Heaven and Hell in previous Arabic literature -- which suggests that several works can belong to some broader collaborative phenomena such as bibliographic families or even traditions and myths. These, however, are not covered by Smiraglia, as his analysis only considers 'the intellectual content of a bibliographic entity', thus leaving out long-term and oral knowledge traditions.
In any case, Smiraglia's discussion of works makes it clear that works indeed have some properties of the level of objectivated spirit, consisting of artefacts and mentefacts. A similar idea is suggested by the BibFrame model, as well as IFLA's Library Reference Model, a harmonization of Functional Requirements for Bibliographic Records and various related conceptual models for authors and subjects (Žumer, 2017). In the Reference Model, a work is 'the intellectual or artistic content of a distinct creation'. It can have different expressions, for example in different media or languages; expressions in turn can be instantiated in various manifestations, like subsequent commented editions of one and the same text; which are published in many identical items (printed copies, digital files, etc.). Again, properties of documents inasmuch as artefacts, such as their publication date or number of pages, only refer to the layer of manifestations, while works as such are conceived as intellectual entities that are beyond their particular expressions and manifestations. Works are carried by documents, such as books, films or web pages, which themselves belong to the lower level of artefacts.
Among the relationships modeled in the Reference Model is the subject relationship (also known as aboutness) between a work and real things (res in Research Model terminology). It is a remarkable fact that this relationship is between res and work, rather than bewteen res and expression or manifestation. That is, the intellectual content of a work is considered to be quite stable, irrespective of its particular instantiations. Although new editions and comments may involve some evolution of the content, its aboutness it estimated to remain basically the same, as a work is originally conceived to express a certain view of reality according to a certain core argumentation. If the work is originally about, say, good and evil in life illustrated in metaphorical ways, it will remain so even in later expressions and manifestations.
The suggestion that works are mentefacts (carried by artifacts) thus appears to be quite correct. Now, which exactly is the relationship between works and mentefacts? Can we simply equate the notion of work with that of mentefacts?
This hypothesis would entail not just that all works are mentefacts, but also that all mentefacts are works. It will be refutated in case it is possible to identify some entities that are mentefacts but not works.
Mentefacts have been described by Eubank, Bidney, Huxley and authors belonging to the Classification Research Group with various examples, although no formal definition is provided (see bibliographical reconstruction in Gnoli, 2018). Eubank's original discussion of mentefacts claims that
[l]anguage as a body of mental concepts (as distinguished from its artifactual form on the written or printed page) comes under this head. The great body of knowledge which the race has accumulated through the centuries belongs here also, as do the systems of thought, the great codes of morals, the great mythologies and philosophies of the world (Eubank, 1932, p. 356-357).
For Bidney (1953, p. 130) mentefacts include language, traditions, literature, moral/aesthetic ideals and intellectual instruments of scientific research. To their continuator Huxley (1955, p. 17-18),
[i]n addition to symbols and works of art, [they] include rituals and formal celebrations, beliefs and superstitions, mythology and theology, tradition and history, philosophy and science. They include the totality of accumulated and available factual knowledge as well as the organized formulations of knowledge provided by mathematics and logic, scientific theories, and philosophical ideas; and finally the assumptions and attitudes that characterize a culture, including the vitally important epistemological premises on which its thinking is conducted.
Some years later, Kyle introduced the term in classification research, claiming to have invented it without reference to the previous authors, to express 'the category of abstract entities such as digit, numeral, equation, maths; letter, alphabet, grammar, syntax, language; value judgment, ethical system, philosophy, etc.' (Kyle, 1965, p. 302).
All these authors provide wider lists of examples, which include works only in an implicit way ('body of knowledge', 'literature'), and rather focus on such broader phenomena as cultural traditions, beliefs, philosophical systems and scientific theories. Works are only part of this corpus, rather than being equivalent to mentefacts. For example, the theory of gravitation is a mentefact that is dealt with in a multiplicity of works.
Some examples, especially by Kyle, also mention entities even smaller than works, like numerals or letters. This was in the context of CRG's application of integrative levels to the classification of cultural entities, so that a sequence of increasing organization could be identified also within them. Numerals and words may be simple units that can be combined to construct increasingly complex mentefacts, like ideas, works, and systems of thought.
Of particular interest to us is Huxley's mention of 'the organized formulations of knowledge provided by mathematics and logic, scientific theories, and philosophical ideas', as this suggests that knowledge organization itself belongs to the level of mentefacts. In this case, its basic units could be concepts, as argued by Dahlberg (1974). In this sense, concepts should be taken not just as notions in the mind of an individual person, but as culturally shared constructions. This leads us to consider the organization of concepts into a knowledge organization system as a mentefact, too.
Knowledge organization systems as mentefacts
Knowledge organization systems are synthetic representations of views of a domain, or of the whole of knowledge, in the form of systems of relationships between concepts. Each knowledge organization system is a model of reality in a special form. It is widely acknowledged that different knowledge organization systems can model reality in different ways according to more or less explicit theoretical assumptions. Indeed, Hjørland (2015) has shown that there is a strict relationship between theories and knowledge organization systems; his paper is even titled 'Theories are knowledge organizing systems'. Now, theories are usually expressed through linear texts, while knowledge organization systems are through schedules and schemes, suggesting that they are different entities. Still, both indeed belong to the level of mentefacts, as the quotes above also suggest.
Knowledge organization systems include components from the personal and social levels: they originate from individual living minds and from certain discourse communities, thus have roots in personal and objective spirit, like all mentefacts have. At the same time, they are not completely determined by these. Rather, they are cultural products that, once produced, have an autonomous existence.
As for its personal component, a knowledge organization system is originally conceived in the mind of its authors, for example the personal spirit of the young Melvil Dewey when working in the library of Amherst College. Also, its content is affected by social factors: for example, the prevalence of Christian culture in the American society of the time, which has led to allocation of eight out of nine subclasses of religion (210/280) to Christianity and only one (290) to all other religions.
Once conceived in individual minds and in a social context, the knowledge organization system can then be written and published. It thus also becomes an artefact, with its particular properties -- the kind of edition, its typographical layout, its translation, distribution, etc. In lack of a suitable organization, it may be poorly known and be at risk of being applied unfrequently and eventually lost, like the history of some high-quality classification systems unfortunately shows. Still, once they are known widely enough, these systems can also be considered as for their intrinsic qualities, leading to acknowledge that, say, such a technical property as a faceted structure is more advanced and performing than the enumerative structure of other systems, despite the more powerful distribution of the latter.
A good knowledge organization system, then, not only reflects the cognitive skills of their creators' personal spirit, as emphasized in a psychological approach, and the cultural perspectives of its creators, as emphasized in social epistemology and domain analysis (Hjørland, 2017). It also needs to prove to be a relatively sound and stable model of knowledge, being corroborated and improved through interaction with external critical factors.
For example, criticism of a knowledge organization system may focus on a check for its consistency in the ordering and combination of concepts. If the same concept, say "tale", has a different position and a different notation in anthropology and in literature, this may lead to inconsistencies in display and retrieval. One such criticism was Jason Farradane's formulation of the principle of unique definition: a concept should be defined at one single place, then reused consistently in other classes.
Criticism may lead to changes in new editions of the knowledge organization system, irrespective of its personal and social origins (the Dewey Decimcal Classification scheme is updated by editorial commitees well after Dewey's death, and is now used in many countries other than 19th century Christian America). Clearly, this kind of knowledge organization system evolution is not due so much to change in authors' knowledge and worldview, as it is to the effectiveness of the knowledge organization system's own properties (e.g. decimal positional notation), that may prove capable of adapting to continuous updates or not. Even more radical criticisms, e.g. against the very conception of a discipline-based structure, could be a challenge to the knowledge organization system's general fitness. Now, properties like decimal notation and disciplinary structure are mentefactual properties, which lie at the level of objectivated spirit.
Intellectual criticism is the particular form of selection to which mentefacts are subject, in the same way as organisms are subject to natural selection by their environment, personal knowledge is subject to selection by individual experience, and social paradigms are subject to selection by public acceptance. Each of these levels evolves under the pressure of a specific form of selection (Gnoli and Ridi, 2014). Indeed, entities at the level of mentefacts, like concepts, works, theories and knowledge organization systems, can all be viewed as conjectures about reality, that can be refuted or corroborated when facing new data, thus evolving in certain ways (Popper, 1969). This process is relatively independent from their personal and social origins, as we have argued for the case of a knowledge organization system. To take an example from a different field, a mathematical theory that has enjoyed a wide social success for some time may later be proven to be wrong after further analysis by new researchers, eventually leading to its refutation.
Just like theories, knowledge organization systems inasmuch as mentefacts should be studied not only in psychological or in socio-epistemological terms, but as a class of objects in their own right, that can be analyzed according to the emergent properties of mentefacts. Indeed, Dahlberg (2013, reported in Ohly, 2018) described knowledge organization as science of science, that is a science dealing with the structure of knowledge as a human product.
Information and the nature of library and information science
As knowledge organization is often considered to be part of library and information science, or at least intersecting it, a related issue is the definition of library and information science as a discipline. What exactly are the object and scope of library and information science? How is library and information science connected to the different levels of reality?
Bawden and Robinson (2018) support Floridi’s philosophy of information as the best foundation for library and information science. Information and data are meant by Floridi in a very basic sense, as fundamental aspects of all reality, 'concrete points of lack of uniformity in the fabric of being' (Floridi, 2011, p. 367). As it has been mentioned in section 1, this corresponds to the basic level of forms or Hartmann's ideal being.
According to Floridi's onto-centric ethics, any information is valuable in itself (Floridi, 2010). However, value can increase as information is organized in increasingly higher levels (Gnoli, 2015). While genetic information, neural information, socially-shared information, technologically-transmitted information and recorded information all are denoted by same term, they have different properties and undergo different evolutionary processes (Gnoli and Ridi,2014). Information in the library and information science sense usually means information contents as organized and recorded in documents (mentefacts recorded in artefacts), or in the personal knowledge of users looking for documents, hence has a narrower meaning than it has in Floridi's philosophy.
A consequence of this seems to be that, while Floridi’s philosophy can indeed be relevant to library and information science, it can be as well to other disciplines dealing with information at different levels, such as genetics (life level), neurobiology (mind level) or information and communication technology (artefacts level). In this respect, the philosophy of information in the basic sense does not seem to have any exclusive relationship with library and information science.
A more specific foundation for library and information science should then be researched at its own particular level, the level of mentefacts. Otherwise, there is a danger that 'others outside the discipline will continue to be the main contributors. This includes a lack of focus on the content aspects of information' (McGuirk, 2009, citing Weissinger, 2005). For example, the material aspects of documents inasmuch as artefacts, like bindings and paper types or file storing and interfaces, are not the core focus of library and information science but are studied by such sciences as, respectively, bibliology and computer science. Library and information science itself, together with such related disciplines as archive science and museology, should be defined as a science of mentefacts. In particular, while artwork mentefacts are studied by architecture, art and literary criticism, library and information science deals with intellectual works.
As we have seen, properties of works are represented, among other sources, in the Library Reference Model. Works have authors, titles, time of production. These properties are indeed described in bibliographies and catalogues, although mixed with such properties of expressions and manifestations as place and time of publication or number of pages. Works have internal structures, such as articulation into parts and sections, and relationships among them. Notably, works (rather than their expressions and manifestations) have subjects, that is they are about certain phenomena treated under certain perspectives. Here is where the strict connection between knowledge organization and library and information science can be found: indeed, real phenomena are ordered by knowledge organization systems, both directly (as in biological taxonomies) and as treated inside works (as in bibliographic classifications). Finally, works are connected with other works which can inspire them, comment about them, cite them, and so on.
The existence of such networks of relationships among works suggests that library and information science yet needs to acknowledge a further, more general class of mentefactual entities, to which myths, traditions, scientific trends and whole knowledge systems probably belong. Indeed, descriptions of the level of mentefacts by earlier authors include this idea, although not in a formalized way yet.
Systems of concepts, beliefs, theories and disciplines are studied in cultural history, in philosophy of science and in knowledge organization taken in the broad sense. With these sciences library and information science could form an alliance, with its focus on the particular mentefactual units that consist in works, as well as on relationships among works and relationships between works and real phenomena.
Riccardo Ridi (Ca' Foscari University of Venice) and two anonymous reviewers have provided useful comments to improve earlier versions of this paper.
About the author
Claudio Gnoli is librarian, researcher in in knowledge organization, teacher of professional courses and active in professional journals and associations. He works at Science and Technology Library, University of Pavia. He can be contacted at firstname.lastname@example.org.
- Bates, M. J. (2002). Toward an integrated model of information seeking and searching. New review of information behaviour research 3, 1-15. Retrieved from https://pages.gseis.ucla.edu/faculty/bates/articles/info_SeekSearch-i-030329.html. (Archived by the Internet Archive at https://web.archive.org/web/20190805101026/https://pages.gseis.ucla.edu/faculty/bates/articles/info_SeekSearch-i-030329.html
- Bawden, D. & Robinson, L. (2018). Curating the infosphere: Luciano Floridi's philosophy of information as the foundation for library and information science. Journal of documentation 74(1), 2-17.
- Bidney, D. (1953). Theoretical anthropology. New York: Columbia University.
- Dahlberg, I. (1974). Grundlagen universaler Wissensordnung. Pullach: Verlag Dokumentation.
- Dahlberg, I. (2013). Desiderate für die Wissensorganisation. In: Ohly, H.P., Wissen – Wissenschaft – Organisation: Proceedings der 12. Tagung der Deutschen ISKO (pp. 12-21). Würzburg: Ergon.
- Eubank, E. E. (1932), The concepts of sociology: a treatise presenting a suggested organization of sociological theory in terms of its major concepts. Boston-New York: Heath.
- Feibleman, J. K. (1954). Theory of integrative levels. The British Journal for the Philosophy of Science 5(17), 59-66.
- Floridi, L. (2010). Information: a very short introduction. Oxford: Oxford University Press.
- Floridi, L. (2011). The philosophy of information. Oxford: Oxford University Press.
- French, S. (2017). The structure of the world: metaphysics and representation. Oxford: Oxford University Press.
- Gnoli, C. (2015). The value added of organized information: from Floridi to Bennett. Paper presented at ISKO UK biennial conference, London, 13-14 July 2015: Knowledge organization: making a difference. Retrieved from https://web.archive.org/web/20181112053504/http://www.iskouk.org/sites/default/files/Gnoli-PaperISKO-UK2015.pdf.
- Gnoli, C. (2017). Classifying phenomena, part 2: Types and levels. Knowledge organization 44(1), 37-54.
- Gnoli, C. (2018). Mentefacts as a missing level in theory of information science. Journal of documentation 74(6), 1226-1242.
- Gnoli, C. & Ridi, R. (2014). Unified Theory of Information, hypertextuality and levels of reality. Journal of documentation 70(3), 443-460.
- Hartmann, N. (1931). Sistematiche philosophie in eigener Darstellung. In Schwarz, H. (Ed.), Deutsche systematische Philosophie nach ihren Gestaltern, Vol. 1. Berlin: Junker und Dünnhaupt.
- Hartmann, N. (1940). Die Aufbau der realen Welt: Grundriss der allgemeinen Kategorienlehre. Berlin: De Gruyter.
- Hjørland, B. (2015). Theories are knowledge organizing systems, Knowledge organization, 42 (2), 113-128.
- Hjørland, B. (2016). Knowledge organization. In Hjørland, B. & Gnoli, C. (Eds.), ISKO encyclopedia of knowledge organization. Retrieved from http://www.isko.org/cyclo/knowledge_organization. Version 1.0 in Knowledge organization 43(6), 475-484. (Archived by the Internet Archive at https://web.archive.org/web/20190805100737/https://www.isko.org/cyclo/knowledge_organization.htm)
- Hjørland, B. (2017). Domain analysis. In Hjørland, B. & Gnoli, C. (Eds.), ISKO encyclopedia of knowledge organization. Retrieved from http://www.isko.org/cyclo/domain_analysis. Version 1.0 in Knowledge organization 44(6), 436-464. (Archived by the Internet Archive at https://web.archive.org/web/20190805100635/https://www.isko.org/cyclo/domain_analysis.htm)
- Hjørland, B. (2018). The foundation of information science: one world or three? A discussion of Gnoli (2018). Journal of documentation 75 (1), 164-171.
- Huxley, J. S. (1955). Guest editorial: Evolution, cultural and biological, Yearbook of anthropology,1955 2-25. Retrieved from http://www.jstor.org/stable/3031134. (Archived by the Internet Archive at https://web.archive.org/web/20190805100535/https://www.jstor.org/stable/3031134)
- Kleineberg, M. (2017). Integrative levels. In Hjørland, B. & Gnoli, C. (Eds.), ISKO encyclopedia of knowledge organization. Retrieved from http://www.isko.org/cyclo/integrative_levels. Version 1.0 in Knowledge organization 44(5), 349-379.
- Kyle, B. R. F. (1965). Review of Atherton, Pauline (Ed.), Classification research: Elsinore, Denmark, 14-18 September 1964: Proceedings of the Second International Study Conference, Munksgaard, Copenhagen, 1965. Journal of documentation, 21 (4), 301-303.
- Ohly, H. P. (2018). Ingetraut Dahlberg. In Hjørland, B. & Gnoli, C. (Eds.), ISKO encyclopedia of knowledge organization. Retrieved from http://www.isko.org/cyclo/dahlberg. (Archived by the Internet Archive at https://web.archive.org/web/20190805100348/https://www.isko.org/cyclo/dahlberg.htm)
- Poli, R. (2001). The basic problem of the theory of levels of reality. Axiomathes 12(3-4), 261-283.
- Popper, K. R. (1969). Conjectures and refutations. London: Routledge and Kegan Paul.
- Žumer, M. (2017). IFLA Library Reference Model (LRM): harmonization of the FRBR family. In Hjørland, B. & Gnoli, C. (Eds.), ISKO encyclopedia of knowledge organization. Retrieved from http://www.isko.org/cyclo/lrm. Version 1.1 in Knowledge organization 45(4), 310-318. (Archived by the Internet Archive at https://web.archive.org/web/20190805100209/https://www.isko.org/cyclo/lrm)