Editing X-machine (section)

=== Communicating X-Machine (CXM) ===
The earliest proposal for connecting several X-machines in parallel is Judith Barnard's 1995 ''Communicating X-machine'' (''CXM'' or ''COMX'') model,<ref
  name="BTWM95">J. Barnard, C. Theaker, J. Whitworth and M. Woodward (1995) 'Real-time communicating X-machines for the formal design of real-time systems', in ''Proceedings of DARTS '95, Universite Libre, Brussels, Belgium, 9–11 November 2005''</ref><ref
  name="Bar96">J. Barnard (1996)
  ''COMX: A methodology for the formal design of computer systems using Communicating X-machines''. 
  PhD Thesis, Staffordshire University.</ref>
in which machines are connected via named communication channels (known as ''ports''); this model exists in both discrete- and real-timed variants.<ref
  name="AldBarn97">A. Alderson and J. Barnard (1997)
  'On Making a Crossing Safe',
  ''Technical Report SOCTR/97/01'', School of Computing, Staffordshire University.
  [http://citeseer.ist.psu.edu/alderson97making.html (Citeseer)]
</ref>  Earlier versions of this work were not fully formal and did not show full input/output relations.

A similar Communicating X-Machine approach using buffered
channels was developed by Petros Kefalas.<ref name="KEK00a">E. Kehris, G. Eleftherakis and P. Kefalas (2000) 'Using X-machines to model and test discrete event simulation programs', ''Proc. 4th World Multiconference on Circuits, Systems, Communications and Computers'', Athens.</ref><ref name="KEK00b">P. Kefalas, G. Eleftherakis and E. Kehris (2000) 'Communicating X-machines: a practical approach for modular specification of large systems', ''Technical Report CS-09/00, Department of Computer Science'', City College, Thessaloniki.</ref>  The focus of this work was on expressiveness in the composition of components.  The ability to reassign channels meant that some of the testing theorems from Stream X-Machines did not carry over.

These variants are discussed [[Communicating X-Machine|in more detail]] on a separate page.