Models of knowledge bases

A model is a consistent set of formal elements that describe an entity. The model helps in solving a number of problems, for example, creating interfaces between a system and a person, and a rough estimate of the system's efficiency.
A domain model (DM) is a part of the real world, displayed as a class or set of classes of real objects.
The construction of the subject area (SbA) model is based on the concept of ontology (the science of being, the science of the nature of things and the relationship between them). From the standpoint of artificial intelligence, the term ontology can be used to define a certain mechanism, a method that is used to describe the SbA, in particular, the basic concepts of this area, their properties and relationships between them. In other words, the ontology consists of the SbD objects divided into clusters according to certain criteria, their definitions and attributes, as well as the inference rules associated with them. The ontology is encoded in such a way that objects and properties are available to software agents.
There is no clear boundary between the knowledge base and the ontology of the SbA. Ontologies can be used to represent knowledge about SbA concepts and hypothesized relationships between them, as well as to describe the content of Web pages. In addition, ontologies can be used to build knowledge bases not only for expert systems, but also for any other applications.

An ontology is a formal specification of a shared conceptualization that takes place in some context of an SbA. At the same time, by conceptualization we will mean, in addition to the collection of concepts, also all information related to concepts - properties, relations, restrictions, axioms and statements about concepts necessary for describing and solving problems in the selected SbA.
The ontology of an SbA defines a formal approximation of conceptualization. In the ontology, that part of the conceptualization is fixed, which depends on the view of the world in relation to a particular area of ​​interest.
Informally, ontology consists of terms and rules for the use of these terms, limiting their meanings within a particular area. At the formal level, an ontology is a system consisting of a set of concepts and a set of statements about these concepts, on the basis of which classes, objects, relationships, functions and theories can be built.
Since there may be different understandings of the same terms in each area, the ontology defines the agreement on the meaning of the terms and is an intermediary between the human-oriented and machine-oriented levels of information presentation. An ontology exists within the framework of agreements between members of the community, for example, between users of some information system. Conceptual (or ontological) modeling deals with the question of how to describe the domain in a declarative, reusable way, the corresponding type dictionaries, how to limit the use of this data, assuming an understanding of what can be inferred from this description.
From this definition it also follows that special cases of ontologies are a simple dictionary, a thesaurus (in which the number of relations between terms is limited).
The ontology model of an SbA consists of a hierarchy of SbA concepts, links between them, and laws that operate within this model.
The following classification features of ontologies are distinguished:
according to the purpose of development;
in the form of presentation;
by owner or user;
by language of description;
by type of relationship;
by area of ​​application.
One of the most popular systems for working with ontologies, created at Stanford University (USA) is Protégé. According to the developers of the Protégé system, all SbA concepts are divided into classes, subclasses, instances. Instances can be either a class or a subclass, and they are described by a frame.
However, the most sophisticated editors and tools cannot perform a meaningful analysis of the ObD and a creative synthesis of ontological structures without the intervention of a cognitive scientist.