Systems biology approach to investigate biological phenomena seems to be very promising because it is capable to capture one of the fundamental properties of living organisms, i.e. their inherent complexity. It allows for analysis biological entities as complex systems of interacting objects. The first and necessary step of such an analysis is building a precise model of the studied biological system. This model is expressed in the language of some branch of mathematics, as for example, differential equations. During the last two decades the theory of Petri nets has appeared to be very well suited for building models of biological systems. The structure of these nets reflects the structure of interacting biological molecules and processes. Moreover, on one hand, Petri nets have intuitive graphical representation being very helpful in understanding the structure of the system and on the other hand, there is a lot of mathematical methods and software tools supporting an analysis of the properties of the nets. In this paper a Petri net based model of the hemojuvelin-hepcidin axis involved in the maintenance of the human body iron homeostasis is presented. The analysis based mainly on T-invariants of the model properties has been made and some biological conclusions have been drawn.

No abstract

Completeness is one of the main quality attributes of requirements specifications. If functional requirements are expressed as use cases, one can be interested in event completeness. A use case is event complete if it contains description of all the events that can happen when executing the use case. Missing events in any use case can lead to higher project costs. Thus, the question arises of what is a good method of identification of events in use cases and what accuracy and review speed one can expect from it. The goal of this study was to check if (1) HAZOPbased event identification is more effective than ad hoc review and (2) what is the review speed of these two approaches. Two controlled experiments were conducted in order to evaluate ad hoc approach and H4U method to event identification. The first experiment included 18 students, while the second experiment was conducted with the help of 82 professionals. In both cases, accuracy and review speed of the investigated methods were measured and analyzed. Moreover, the usage of HAZOP keywords was analyzed. In both experiments, a benchmark specification based on use cases was used. The first experiment with students showed that a HAZOP-based review is more effective in event identification than ad hoc review and this result is statistically significant. However, the reviewing speed of HAZOP-based reviews is lower. The second experiment with professionals confirmed these results. These experiments showed also that event completeness is hard to achieve. It on average ranged from 0.15 to 0.26. HAZOP-based identification of events in use cases is an useful alternative to ad hoc reviews. It can achieve higher event completeness at the cost of an increase in effort.

No abstract

No abstract