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Lightweight models for interpreting informal specifications

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Abstract

We explore the use of lightweight models, namely those in PROMELA/SPIN, by software engineers within the life cycle of software development. The primary goal is to improve the interpretation and understanding of an informal specification, not necessarily to validate the specification. We give details of an example involving an informal specification of an application protocol in telecommunications, namely the Request for Comments (RFC) standard for the Trivial File Transfer protocol (TFTP). We show how we were able to use this type of modelling in an iterative process, using tools that facilitate the process.

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Notes

  1. This scenario identified using the simple model in Fig. 3 has actually been the source of difficulties in several implementations of TFTP. For example, there is a documented bug in Sun Solaris 5, ID#1110881: "Tftp cannot get file of 16 MB over and up." This bug was due to an incorrect data type in a C include file (tftp.h). The type for the block number in the DATA and ACK messages was incorrectly defined as "short", which is a signed value, as opposed to "unsigned short". Because the block number was (incorrectly) signed, it would become "negative" in the logic of the software during the transfer of a file of more than 16 MB.

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Acknowledgements

I wish to thank the students of the winter 2001 semester of LOG540 Analyse et conception de logiciels de télécommunication at the ÉTS for their courage, patience and helpful feedback as pioneer students in our Software Engineering bachelor's program.

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Authors and Affiliations

  1. Electrical Engineering Department, École de technologie supérieure, 1100 rue Notre-Dame Ouest, Montréal, QC H3C 1K3, Canada

    Christopher P. Fuhrman

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  1. Christopher P. Fuhrman
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Correspondence to Christopher P. Fuhrman.

Appendix

Appendix

Promela source code for initial model (Fig. 12)

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Promela source code for refined model (Fig. 13)

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Fuhrman, C.P. Lightweight models for interpreting informal specifications. Requirements Eng 8, 206–221 (2003). https://doi.org/10.1007/s00766-002-0154-9

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