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The Hard Real-Time Unified Modeling Language (HRT-UML) method, and the supporting toolset, aims at providing a comprehensive solution to the modeling of hard real-time and dependable systems and their early verification, according to rigorous techniques based on formal theories, such as schedulability analysis and simulation, formal verification and quantitative evaluation of dependability attributes.


Extending UML for HRT and dependability support

  • Experience shows that the design of Hard Real-Time systems needs methodologies suitable for the modeling and analysis of aspects related to time, schedulability, performance, and RAMS (Reliability, Availability, Maintainability, Safety). In the context of the European Aerospace community a reference for the modeling of hard real time systems was the Hard Real-Time-HOOD (HRT-HOOD) method, recommended by the European Space Agency (ESA) for the development of on-board systems. Meanwhile, in recent years the Unified Modeling Language (UML) has been gaining very large acceptance in a wide range of domains, all over the world, becoming a de-facto international standard.
    HRT-UML defines a customized version of UML to express and improve the HRT-HOOD methodology. The resulting design method, together with its support toolset, permits static scheduling analysis of the system and also caters for automated generation of consistent code. A relevant aspect of HRT-UML is the integration of design activities with selected methods for the development of dependable systems. The approach is to assist the designer by offering an appropriate design methodology and a support toolset, that integrates dependability validation techniques based on formal verification of system behavioral properties by model-checking, modeling of dependability aspects and well established techniques for quantitative assessment of system dependability attributes, automatic translations from the design to the mathematical models and the analysis tools that are most appropriate for the different kinds of validation, the SPIN model-checker and the Möbius behavior modeling tool.
    Support is offered by HRT-UML also for the development of systems with control aspects, by integrating major lifecycle activities such as functional control design made with Simulink, with software/hardware architecture design and validation through analysis and co-simulation.

Key Features HRT-UML features include: 

  • software design taking into account both functional and timing requirements; 

  • design verification using rigorous techniques 

  • schedulability analysis and simulation or formal model-checking 

  • quantitative evaluation of RAMS properties 

  • combined simulation of control aspects 

  • generation of consistent code 

  • Ada 95

  • Ada 95 compliant with Ravenscar Profile

  • C for standard OSEK/VDX RTOSs

HRT-UML Design Principles
The focus of an HRT design is not the definition of classes but rather the set of objects that compose the system and their interconnections. Interacting objects are organized in a structure according to the following principles:

  • Object Modeling Prevalence

  • Multiple Static Instances

  • Hierarchical Decomposition 

  • User-Provider Relationships

In this way, HRT-UML enables: 

  • easy decomposition of the software architecture into design objects having internal parts that communicate with each other and with the outside environment, 

  • explicit recognition of the typical activities of real-time systems such as cyclic and sporadic threads, protected resources

  • association of timing and dependability properties to objects, so as to enable schedulability and dependability analysis.

The HRT-UML run-time platform is developed entirely in Java and can be installed on Windows and Linux based systems. Portable Java technology, makes it possible to migrate to other open systems with a only limited effort.

Developed through R&D projects co-funded by the Italian Space Agency and the EC, HRT-UML evaluation and enhancements activities were supported by the European Space Agency Research and Technology Centre. HRT-UML has already been widely employed by representative industries from the European Space software community.

Mazzini S., D’Alessandro M., Di Natale M., Domenici A., Lipari G., Vardanega T. “HRT-UML: taking HRT-HOOD into UML”, Proceedings of 8th Conference on Reliable Software Technologies Ada Europe, 2003.

Mazzini S., Latella D., Viva D., “PRIDE: an Integrated Software Development Environment for Dependable Systems”, Proc. of the DASIA Conference, 2004

Mazzini S., D’Alessandro M., Di Natale M., Vardanega T., “Component-Based Real-Time Design: Mapping HRT-HOOD to UML”, Proceedings of 30th Euromicro Conference, 2004.

Mazzini S., Favaro J., Puri S., Bavaro M., “Software Methodological and Tool Support for Embedded Control Systems”, Proc. of the “Adaptability Techniques for Control System Software” session of the IFAC Conference, 2005.