The UML is an influential and widespread notation for high-level modelling
of information processing system. UML statechart diagrams are a graphical
language to describe system behaviour. They constitute one of the most
intensively used formalisms comprised by the UML. However, statechart
diagrams are lacking concepts for describing real-time, performance,
dependability and QoS characteristics at a behavioural level.
In this tutorial, we present a QoS-oriented extension of UML statechart
diagrams, called StoCharts. StoCharts enhance the basic statechart
formalism with two distinguished features, both being simple and easy to
understand, yet powerful enough to model a sufficiently rich class of
stochastic decision processes. This is illustrated by a selection of case
studies performed using StoCharts. We review the main ingredients of
StoCharts and explain different approaches to evaluate QoS requirements
satisfied by a collection of StoCharts. In particular we emphasize how a
rigid formal semantics makes it possible to employ stochastic model
checking to verify QoS requirements.