UML (Unified Modeling Language, [3]) is the most recently created modelling language of object-oriented systems which covers the entire functional design process and comprises a variety of formalisms adapted to the engineer's way of thinking, hierarchical model refinement and design re-use. However, UML based design environments do not support yet the assurance of the quality of service during the design processes. Dependability, performance and conformance to the initial specification are properties that usually require specialised expert groups to be checked and validated. UML, as a language intended to be understood also by machines and tools, should support automatic model-based analysis and validation of the above properties. Our project HIDE (High-Level Integrated Design Environment for Dependability) aims at analysing dependability attributes (reliability, availability and safety) by means of transformations from UML descriptions to stochastic and concurrency semantics models. To do this, the necessary model parameters and design structures important for dependability analysis have to be identified, necessary extensions of UML defined and the approach and algorithm of the transformations elaborated. In the current phase of the project, we focus on the early dependability modelling based on high-level, structural descriptions. Modelling in the early design phases allows comparing different solutions, to select the most suitable one, and to highlight problems in the design. Modelling of complex systems consisting of a large number of hardware and software components and including also redundancy structures may introduce complexity problems. A feasible approach is to start with simple, high-level models and make them more and more complex by refining the critical parts of the system. Accordingly, we are focusing on a subset of UML consisting of the static structure diagrams (class, object, component and deployment diagrams). Redundancy structures providing fault tolerance are restricted to class-level ones, i.e. a distinguished controller object is used to coordinate the objects (usually variants) providing services in a redundant way [4]. Note that these redundancy structures may be available for the designer in the form of predefined library elements or schemes. Behavioural diagrams are not considered, they are used only in the case of controllers to derive the (static) relations of the objects being co-ordinated. The formalism of the target dependability model is a timed transition Petri-net.