The ESSaRel project is committed to developing modelling techniques and corresponding tools
for the quantitative analysis of safety, reliability and availability of embedded systems. It was founded in 2002
by Bernhard Kaiser as a student project at the chair for Software Engineering and Quality Management
(Prof. Dr. Liggesmeyer). Later it emerged to a continuous research and tool development project and in 2005 it
was moved to Fraunhofer IESE, Kaiserslautern, where the development
is continued at the TU Kaiserslautern, department (AG)
Software Engineering: Dependability.
Centred around the core technologies fault tree analysis and probabilistic state based models we
have eleborated and integrated models that particularly fit the software aspects of modern embedded systems, integrating
smoothly with the software engineering process. The construction of tools for industrial application in tight cooperation
with our industrial partners is an integral part of our research activities. UWG3 is an industry-proven fault tree analysis
tool, its successor ESSaRel is additionally able to integrate different models (fault trees, Markov chains) and will support
the novel state/event fault tree (SEFT) approach in the future.
The concepts developed so far comprise Component fault trees (CFT)
the integration of CFT and Markov chain models, and State/event fault trees (SEFT)
CFT are a concept for assigning arbitrary parts of fault trees to technical components and to model them separately, even if
they are no independent subtrees. The components are joined by input and output ports and can be stored in libraries or XML
files along with other component data for later reuse. The component concept also makes quantitative evaluation more efficient.
The expressive power of CFT is the same as of traditional fault trees, but the trees are extended to acyclic
directed graphs, allowing consistent handling of repeated events. By adding Markov models as subcomponents to CFT, the resulting
hybrid models are able to represent multimodal and degrading failure behaviour. The (hybrid) CFT concept has been integrated
into our tools ESSaRel and UWG3.
SEFT extend the expressive power of fault trees by a notion of states and events, allowing the modelling
of state dependencies and temporal relations of events not possible in classical fault trees. Models from software engineering
tools can be integrated into safety or reliability analysis. Implementation of SEFT inside the ESSaRel framework is ongoing.
We offer our tools free of charge for universities and research institutes and for
evaluation purposes; if you consider commercial application please contact us.
The UWG3 tool
UWG3 is a user-friendly Windows-based fault tree analyser. It offers both quantitative (failed states probabilities and
failure rates) and qualitative (cut set listing) evaluation, based on fast BDD algorithms. The tool development started in
2002 as a student project at the Hasso Plattner Institute, sponsored by Siemens AG
and DaimlerChrysler AG. The initial mission was to create a successor for the fault tree analyser UWG2, a non-public tool
used by Siemens corporation.
Since quality and ergonomics were the predominant goals we decided to write the new version UWG3
from scratch (in C# language, based on Microsoft's .NET framework). UWG3 (like ESSaRel) fully incorporates the component/CFT approach.
Development by components makes large projects much easier to manage. The state-of-the-art Windows user interface distinguishes
ESSaRel and UWG3 from most other tools developed in a research context. Since 2003 UWG3 has been used in several industrial
projects at Siemens, proving its intuitive handling from the start. Since 2004 the second release is available for download,
offering a set of new features. The use of UWG3 for research, teaching and evaluation is free of charge.