Knowledge model

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A representation of knowledge used to understand and communicate an aspect of knowledge in the real world. Note: In the literature, a Knowledge Model often refers to the way a knowledge domain may be described by Knowledge Organization Systems. For these types of techniques, please refer to knowledge representation.


Numerous knowledge models exist to describe different important aspects of knowledge for the purposes of understanding and communication. A number of models which are commonly used in describing knowledge are described here. The models emphasize different elements of knowledge and represent them at different levels of complexity.

In the same way that an automotive vehicle may be described in terms of many dimensions such as:

  1. Materials: Metal, Rubber, Glass etc.
  2. Components: Wheels, Engine, Passenger compartment, etc.
  3. Colours : Black, Red, Grey etc.

So also can Knowledge be described in terms of a number of different dimensions such as:

  1. Domains – technical, organisational, societal etc.
  2. States – Explicit, implicit, tacit etc.
  3. Levels – Know-why, know-how, know-what etc.
  4. Representations – Documents, models, pictures etc.
  5. Categories – Good practices, lessons, standards etc.
  6. Artefacts – Buildings, tools, equipment, etc.

Some models illustrate only the major components of knowledge, others also illustrate systems, subsystems and even processes. This article describes some of those that have been used in IAEA publications in an ascending order of complexity.

The models can be classified into two major groups.

  1. Component models: where knowledge is described as being composed of two or more parts
  2. Hierarchical models: where knowledge can be processed into different types with increasing rarity, value and quality

Component models

Tacit-Explicit spectrum models

Expanding on the idea originally published by M. Polanyi [1], it is useful to identify three types of knowledge: Explicit, tacit and implicit. Each requires different approaches to its management.

  • Explicit is Knowledge that has been articulated or has already been codified in some form
  • Implicit is Implicit knowledge is held in a person’s mind; it is the knowledge which has not yet been captured or transferred in any form. Knowledge that people carry in their heads.
  • Tacit is The knowledge wholly embodied in the individual and is rooted in practice, experience, intuition and individual skills that is difficult or even impossible to recall, articulate and thus to transfer.

The models cover the spectrum from tacit knowledge (Fig. 1), i.e. the knowledge that resides within a person, and explicit knowledge, that has been articulated or has already been codified in some form.

A simplified, but popular model is the Iceberg model (Fig. 2), which depicts the relationship between explicit and tacit knowledge - the implicit knowledge is subsumed under tacit knowledge, a simplification often found in the literature.

In some more detailed models, explicit knowledge is further divided into codified and non-codified explicit knowledge, referring to knowledge which is already codified, or knowledge which could be codified. However, this distinction is not often made and of limited usefulness.

The Three Worlds Model of Karl R. Popper

A broad foundation in understanding knowledge has been laid by the philosopher Karl Popper [2] with his Three World Model (Fig. 3):

  • World 1 (existence and reality) is the physical universe. It consists of the actual truth and reality that we try to represent, such as energy, physics, and chemistry. While we exist in this world, we do not always perceive it and then represent it correctly.
  • World 2 (subjective knowledge) is the world of our subjective personal perceptions, experiences, and cognition. It is what we think about the world as we try to map, represent, and anticipate or hypothesis in order to maintain our existence in an every changing place. Personal knowledge and memory form this world, which are based on self-regulation, cognition, consciousness, dispositions, and processes. Note that Polanyi's theory of tacit and explicit knowledge is based entirely within this world.
  • World 3 (objective knowledge) is the sum total of the objective abstract products of the human mind. It consists of such artifacts as books, tools, theories, models, libraries, computers, and networks. It is quite a diverse mixture. While knowledge may be created and produced by World 2 activities, its artifacts are stored in World 3, for example a claw-hammer, Maslow's hierarchy of needs, and Goedel's proof of the incompleteness of arithmetic. Popper also includes genetic heredity (if you think about it, genes are really nothing more than a biological artifact of instructions).


A priori, a posteriori knowledge model

A priori knowledge is independent of experience (theoretical knowledge).

A posteriori knowledge is dependent on experience or empirical evidence (practical knowledge).

See also:

Hierarchical models

Data, information, knowledge, (wisdom) model

Raw data become information in the context of creation, information becomes knowledge in the context of use, meaning that a human agent with the appropriate background is required. Sometimes, the data, information, knowledge model is extended with the level of wisdom, as knowledge may eventually lead to wisdom (

Know-how, Know-why, Know-what models

This is sometimes referred to as the knowledge level model. Know-how usually refers to Know-howThis means Skill Know-what is Know-what Know-why refers to Know-why. A simple example to illustrate this is the need for different types of knowledge when jumping into deep water. Know-how is the ability to swim, know-what is knowing what arm and leg actions are required as they may be presented in a written instruction manual on swimming. Know-why may include an understanding of Archimede's principle and Newton's third law.

This model can be extended to include other aspects of knowledge by adding know-who, know-when, know-where.

Proficiency, codification, diffusion model

Knowledge has three attributes whose values can be managed by knowledge management. These three attributes are:

  1. level of proficiency (P)
  2. level of codification (C)
  3. level of diffusion (D)

Proficiency refers to how much of a particular capability a person or team has. It is the degree of mastery of a skill or area of knowledge. Codification refers to the transformation of knowledge into a human-readable format. Diffusion refers to the number of people who hold knowledge in any given area and the means to spread that knowledge.

Domains knowledge model

All knowledge can be subdivided onto knowledge domains. Each is the content of a particular field or area of knowledge. In knowledge management, domains are often modeled by means of Knowledge Organization Systems, and are particularly useful for organizing knowledge repositories and knowledge portals.

Declarative, procedural knowledge model

Declarative, also descriptive knowledge or propositional knowledge, is the type of knowledge that is, by its very nature, expressed in declarative sentences or indicative propositions. This distinguishes descriptive knowledge from what is commonly known as "know-how", or procedural knowledge (the knowledge of how, and especially how best, to perform some task), and "knowing of", or knowledge by acquaintance (the knowledge of something's existence). (Wikipedia,


[1] Polanyi, M. (1958): Personal Knowledge: Towards a Post-Critical Philosophy. University of Chicago Press, Chicago

[2] Popper, K. (1972): Objective Knowledge: An Evolutionary Approach, Oxford Univ Pr; Auflage: Revised. (9. November 1972)

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