iSPN: An integrated environment for modeling using stochastic Petri nets

Interaction with computers has come a long way since the archaic textual interfaces There is now substantial literature on computer interaction HCI a research subject widely recognized as a vital component of successful computer ap plications But when we evaluate HCIs currently available on analytical modeling packages we real ize the enormous gap perceived between their in terfaces and modern HCI trends The developers of analytic modeling packages need to deliver ben e cial services to the user and deliver them in a usable way This paper suggests an approach of delivering this next generation of modeling tools with improved HCI The approach is followed in the development of an integrated environment for modeling using Stochastic Petri Nets named iSPN Careful consideration was given to the design and implementation of iSPN to facilitate the creation of SPN models iSPN increases the power of SPNP the Stochastic Petri Net Package by providing a means of rapidly developing stochastic reward nets SRNs the model type used for input In put to SPNP is speci ed using CSPL C based SPN Language but iSPN removes this burden from the user by providing an interface for graphical repre sentation of the model The use of Tcl Tk in designing iSPN makes this application portable to all platforms Supported by grants from the Lord Foundation by a Duke University Research Instrumentation award and by a core project of the Center for Advanced Computing and Communication ySupported in part by a GTE Fellowship manager database DATA BASE control control/data nomenclature: iSPN translator output graphical browse examples Petri net credits display welcome display SPNP control SPNP editor modeling environments Figure iSPN main software modules Development Strategy iSPN mimics the look and feel of real le cabinet drawers by using windows with title tabs to ease the sorting of overlapping windows The HCI design model of iSPN is based on modern premises that design should i be user centred and involve users as much as possible so that they can in uence it ii integrate knowledge and expertise from the di erent disci plines that contribute to HCI design and iii be highly iterative so that testing can be done to check that the design does indeed meet users requirement Designing the HCI of iSPN based on the established premises is ensured by the appropriate selection of design model We use the one proposed by Hix and Harston known as the star life cycle see Figure This life cycle w as selected particularly because it encourages iter ation The central point of the star design cycle is evaluation which is viewed as relevant at all stages of the life cycle and not just at the end of the HCI development as traditional software product developments suggest All aspects of systems de velopment are subjected to constant evaluation by users and by experts Another reason for the selec tion of the star life cycle is its natural orientation on being supportive of both top down and bottom up de velopment A feature extremely important in iSPN since the development of some of its components starts from the underlying modeling tools such as SPNP and progresses upward towards the user while the specialized interfaces e g for the net work appli cation follow exactly the opposite direction Yet another contributing reason is that the star life cy cle also stresses rapid prototyping and an incremen tal approach towards the nal product The rapid prototyping approach adopted in iSPN deals directly with the problem of needing to check that the users requirements are being met by the design at di erent stages New design ideas can be exercised and commented on by users before a gre at deal of expensive development work is com pleted Besides the prototyping approach helps the HCI designers to cope with the problem of un derstanding requirements conceptual design/ formal design evaluation task analysis/ functional analysis prototyping implementation requirements specification Figure The star life cycle Software organization The major components of the iSPN interface see Figure are a Petri net editor which allows graph ical input of the stochastic Petri nets and an exten sive collection of visualization routines to analyze output results of SPNP and aid fo r debugging Each module corresponds to a page in the software