Executable Modeling: Retrospective and Prospective
                                                            (Keynote)
                                                        Stephen Mellor
                                           Email: StephenMellor@StephenMellor.com



  Index Terms—Executable Models; Action Languages; UML                 can have confidence that the combined component works. We
                                                                       need this now we are connecting industrial control systems to
                          I. A BSTRACT
                                                                       the Internet. Composable execution units are needed to bring
   In the mid-Eighties, there were thirty object-oriented nota-        executable modeling to growing industrial applications.
tions and thirty object-oriented methods. These fell into three
main groups: sketches of software structure, depictions of soft-                              II. B IOGRAPHY
ware (usually with gaps to fill in the code) and what we now                                       Stephen Mellor is the Chief Tech-
call executable models. By the late-Nineties, there was one                                     nical Officer for the Industrial In-
notation and zero methods. Executable models were hard to                                       ternet Consortium, where he directs
find. The method wars were over. We (all) lost. Worse, models                                   the standards requirements and tech-
as graphical descriptions of code are “just documentation”,                                     nology and security priorities for
overhead that gets in the way of the real thing: code. The Agile                                the Industrial Internet. In that role,
Manifesto of 2001 elevates “working software” over models.                                      he coordinates the activities of the
But “software” can also mean executable models.                                                 several engineering, architecture, se-
   The difference between a programming language and an                                         curity and testbed working groups
action language is, as always, the level of abstraction. Pro-                                   and teams.
gramming languages are “aware” of data structures and threads                                      He is a well-known technology
of control. Action languages can abstract these away. Over                                      consultant on methods for the con-
more than a decade an action language has been added to UML                                     struction of real-time and embedded
and open-source implementations made available. Defined                                         systems, a signatory to the Agile
semantics are now on the horizon for state models. Perhaps             Manifesto, and adjunct professor at the Australian National
UML can be made executable after all.                                  University in Canberra, ACT, Australia. Stephen is the author
   That will help, but it’s not enough. We need our executable         of Structured Development for Real-Time Systems, Object
models to be composable so that when two components have               Lifecycles, Executable UML, and MDA Distilled.
been tested and the manner of their interactions tested too, we




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