1. The Hard Real-Time Unified Modeling Language (HRT-UML) method provides a comprehensive solution to the modeling of Hard Real Time systems. HRT-UML incorporates all the advantages of the HRT-HOOD method and improves the HRT-HOOD design concepts by converging to a more powerful and expressive standard UML modeling notation. HRT-UML allows the user:  to design the system taking into account functional requirements  to design the system taking into account timing requirements  to analyse the schedulability of the system  to generate a consistent mapping into the implementation

2. Merging the UML and HRT-HOOD methods The experience shows that the design of Hard Real-Time systems needs methodologies suitable for the modeling and analysis of aspects related to time, schedulability and performance. In the context of the European Aerospace community a reference method for design is Hierarchical Object Oriented Design (HOOD) and in particular its extension for the modeling of hard real time systems, Hard Real-Time- Hierarchical Object Oriented Design (HRT-HOOD), recommended by the European Space Agency (ESA) for the development of on-board systems. On the other hand in recent years the Unified Modeling Language (UML) has been gaining a very large acceptance in a wide range of domains, all over the world, becoming a de-facto international standard. In the aerospace domain the common opinion is that UML, as a general notation, is not suitable for Hard Real Time systems, even if its importance is recognized as a standard and as a technological trend in the near future. HRT-UML replaces the HRT-HOOD method with a customized version of UML, that incorporates the advantages of both standards and complements the weak points. This approach has the clear advantage of making HRT-HOOD converge on a more powerful and expressive modeling notation. Contact: Silvia Mazzini Intecs HRT S.p.A. Via Gereschi 34 56127 Pisa — Italy Tel +39 050 545 282 Fax +39 050 545 200 silvia.mazzini@pisa.intecs.it HRT-UML Design Principles A HRT-UML project is composed of a set of interacting objects which are organized in a structure according to several principles:  Structural Decomposition objects may be decomposed into other objects, so that the system can be represented as an include graph or parent-child hierarchy of objects  User-Provider relations objects may use services of other objects, so that the system can be represented as a use graph or user-provider hierarchy of objects  Object Nested Notation includes the operation compartment to avoid users to use class diagrams to describe the system and an optional compartment showing the object decomposition to allow users better understand the system topology;  Multiple Static Instances objects may have the same structure and properties but differ in their attribute values and state evolution. Tool Features  Specialized graphical editing: graphical representation of the topological structure of the system and transparent object structural decomposition  XMI standard compliancy: projects saving is based on the standard UML exchange text format (XMI/XML).  Code generation: production of Ada 95 code using customizable templates.  Schedulability analysis: support for timing simulation and worst case schedulability analysis. The HRT-UML tool is fully implemented in Java, assuring portability across platforms.