This paper examines and analyzes approaches for constructing network of terms as an ontological subject domain model. In particular, new approaches and rules for determining the syntax and semantic links between terms in the text and the directions of these links between nodes in undirected networks of terms constructed from terms of a thematic text corpus, are proposed and researched. Also, one of the methods for creating terminological ontologies . the algorithm for building the thematic networks of natural hierarchies of terms based on analysis of texts corpora - is considered and used to build a directed network of words and phrases (separate unigrams, bigrams and threegrams). The wellknown fairy tale "The story of Little Red Riding Hood" is provided as examples to demonstrate an accuracy of the proposed rules. The Python programming language and its separate functions of a specialized add-in - the module NLTK (Natural Language Toolkit open source library) is used to create the software realization of the proposed and considered approaches and methods. Using the software for modelling and visualization of graphs - Gephi, the built directed networks of terms were visualized for better visual perception. The proposed approach can be used for automatically creating terminological ontologies of subject domains with the participation of experts. Also, the research result can be used to create personal search interfaces for users of information retrieval systems and also can be used in navigation systems in databases. It should help users of such systems simplify the process of searching the relevant information.

Keywords: Subject Domain, Terminological Ontology, Network of Terms, Horizontal Visibility Graph, Network of Natural Hierarchies of Terms, Syntax and Semantic Links, Undirected Network, Directed Network.