The subject of this thesis is the development of the object-oriented design process model framework. The proposed framework should be used as an open toolbox, independently of the design task class and the design process phase. In such an approach, every occurrence, relation and other real-world 'things' from the domain of the design process are attempted to be modelled as objects. It is assumed that the object-oriented methodologies can provide more appropriate and flexible ways of software system modelling than the other techniques. The design process is here viewed as a sequence of transitions from an initial state of data, constraints and goals to a final state: a complete description of the mechanical artefact being designed. These transitions are allocated to individual participants or teams, and individual or integrated computational tools or models. The main results of this research are identification and description of the basic structural, relational and behavioural entities of the design process model. The proposed model is built upon following basic structural entities: design parameter, product description object (any type of document), product structure object (part), interface to external software tool, action, designer (as an ""actor"" in the process) and the design task. These entities are modelled as the basic classes of the object-oriented design process model. The complex network of relations between design process model entities is analysed as a central issue of the presented research. It turned out that a very large and complex object network could be efficiently modelled and managed in an object database environment. Thus, a design process model is built using a ""bottom up"" approach in which the basic structural entities and the network of relations are used as a building blocks for more complex entities which model and control the design process flow. A design process is represented with design plan - a collection of nodes and their connections in a directed graph. The connections between nodes represent the information flow and/or the preplanned execution paths. Possible design plan topologies, the plan generation and exploitation issues are discussed, as well as the possibilities of implementing dynamic changes while the plan is being executed. A design plan node models one step of the design process, including: checking of preconditions, list of actions, checking the postconditions and deciding about the next step. Preconditions and postconditions include sets of constraints and rules. Constraints and rules include references to design parameters and attributes of all classes of objects that constitute the design process model. The structure of the proposed model is documented in the UML language, using "Rational Rose 2000" software tool. An example of ""real world" implementation is realised in POET object database.