The existing information systems and their associated databases cannot accept the knowledge written in sentences in natural language. Based on the conceptual framework Node of Knowledge (NOK), a new system based on the NOK method is analysed and modelled. It will save textual knowledge from natural language sentences into its database (DBNOK) without loss of semantics. In addition, a system based on NOK method can also accept questions in the form of interrogative sentences of natural language, and based on the knowledge stored in DBNOK, provide answers to the questions. The aim of this paper is to enrich existing information systems and their databases with a system for the reception and representation of knowledge written in texts using simple sentences of natural language; i.e. with a system that is based on the conceptual framework of "Node of Knowledge". The integration of two systems allows the addition of new knowledge related to the data in the database of the existing information system without changing the existing database schema. The result of this expansion is an integral, semantically richer database. The paper defines the conceptual framework "Node of Knowledge". Rules for transformation of declarative and interrogative sentences in natural language into FNOK and QFNOK records are defined. Also, models of the system based on NOK method, algorithms for transformation of FNOK and QFNOK records into a relational database and an algorithm for creating answers are defined. A model of an integrated database, i.e. a database of the existing information system that is integrated with a system which allows entering knowledge expressed in sentences in natural language is developed. It is now possible to define questions in natural language which include knowledge of both systems. Queries are connected to both databases. In addition, it is possible to obtain answers to the set questions.