13,510 research outputs found
On a Graph-Based Semantics for UML Class and Object Diagrams
In this paper we propose a formal extension of type graphs with notions that are commonplace in the UML and have long proven their worth in that context: namely, inheritance, multiplicity, containment and the like. We believe the absence of a comprehensive and commonly agreed upon formalisation of these notions to be an important and, unfortunately, often ignored omission. Since our eventual aim (shared by many researchers) is to give unambiguous, formal semantics to the UML using the theory of graphs and graph transformation, in this paper we propose a set of definitions to repair this omission. With respect to previous work in this direction, our aim is to arrive at more comprehensive and at the same time simpler definitions.\u
Generating natural language specifications from UML class diagrams
Early phases of software development are known to be problematic, difficult to manage and errors occurring during these phases are expensive to correct. Many systems have been developed to aid the transition from informal Natural Language requirements to semistructured or formal specifications. Furthermore, consistency checking is seen by many software engineers as the solution to reduce the number of errors occurring during the software development life cycle and allow early verification and validation of software systems. However, this is confined to the models developed during analysis and design and fails to include the early Natural Language requirements. This excludes proper user involvement and creates a gap between the original requirements and the updated and modified models and implementations of the system. To improve this process, we propose a system that generates Natural Language specifications from UML class diagrams. We first investigate the variation of the input language used in naming the components of a class diagram based on the study of a large number of examples from the literature and then develop rules for removing ambiguities in the subset of Natural Language used within UML. We use WordNet,a linguistic ontology, to disambiguate the lexical structures of the UML string names and generate semantically sound sentences. Our system is developed in Java and is tested on an independent though academic case study
Superbubble evolution in disk galaxies, I. Study of blow-out by analytical models
Galactic winds are a common phenomenon in starburst galaxies in the local
universe as well as at higher redshifts. Their sources are superbubbles driven
by sequential supernova explosions in star forming regions, which carve out
large holes in the interstellar medium and eject hot, metal enriched gas into
the halo and to the galactic neighborhood. We investigate the evolution of
superbubbles in exponentially stratified disks. We present advanced analytical
models for the expansion of such bubbles and calculate their evolution in space
and time. With these models one can derive the energy input that is needed for
blow-out of superbubbles into the halo and derive the break-up of the shell,
since Rayleigh-Taylor instabilities develop soon after a bubble starts to
accelerate into the halo. The approximation of Kompaneets is modified in order
to calculate velocity and acceleration of a bubble analytically. Our new model
differs from earlier ones, because it presents for the first time an analytical
calculation for the expansion of superbubbles in an exponential density
distribution driven by a time-dependent energy input rate. The time-sequence of
supernova explosions of OB-stars is modeled using their main sequence lifetime
and an initial mass function. We calculate the morphology and kinematics of
superbubbles powered by three different kinds of energy input and we derive the
energy input required for blow-out as a function of the density and the scale
height of the ambient interstellar medium. The Rayleigh-Taylor instability
timescale in the shell is calculated in order to estimate when the shell starts
to fragment and finally breaks up. Analytical models are a very efficient tool
for comparison to observations, like e.g. the Local Bubble and the W4 bubble
discussed in this paper, and also give insight into the dynamics of superbubble
evolution.Comment: 18 pages, 11 figure
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