The book is an introduction to object-oriented modeling and is dedicated to modeling the structures of object software systems. It is based on the principle "from model to code", which focuses the creative efforts at the stage of model synthesis. When the model is synthesized, the task is essentially solved and the code is needed to 'materialise' the solution found. The more formally the model is specified, the easier it is to display it in the software code. The book uses modeling tools, which are a combination of the unified modeling language UML and the OCL object restriction language, which are often the actual standard for developing software projects. The book is aimed at two categories of readers: (1) specialists studying object-oriented modeling as a means of developing formalised models of poorly formalised systems; (2) programmers starting to study object-oriented programming.