o c e

ng re computational methods [21–30]. Practical computational modelling requires the use of times accompanied by instructions for obtaining the model definitions in electronic form. However, because each authorsoftware tools. To be useful as formal embodiments of our understanding of biological systems [31], computational models must be put into a form that can be communicated effectively between the software tools used to work with may use a different modelling environment (and model representation language), such definitions are often not straightforward to examine, test and reuse. If a researcher wishes to use a published model, the researcher typically must manually transcribe the model into a different format.. When simulators are no longer supported, models developed in those systems can become stranded and unusable. This has already happened on a number of occasions, with a resulting loss of usable models to the community. Continued innovation and development of new tools will only aggravate this problem unless the issue of standard formats is addressed. We developed the Systems Biology Markup Language (SBML) in an effort to address these problems. SBML is a format for representing computational models in a way that can be used by different software systems to communicate and exchange those models [32, 33]. By supporting SBML as an input and output format, different software tools can all operate on an identical representation of a model, removing opportunities for errors in translation and assuring a common starting point for analyses and simulations. The SBML project is not an attempt to define a universal language for representing quantitative models; the fluid an