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duce any ad hoc elements that would be questionable if they were to be
included into a standard proposal.
•
Maximality
. ASMs are expressive enough to model any aspect around com-
putation.
•
Formality
. ASMs provide a rigid framework to express dynamics.
In the following, we present a short overview of ASMs and then address
the core conceptual model for WSMO choreographies.
Basic Abstract State Machines
Abstract state machines, formerly known as evolving algebras [58], provide a
means to describe systems in a precise manner using a semantically well-
founded mathematical notation. The core principles are the definition of
ground models and the design of systems by refinements. Ground models
define the requirements and operations of the system, expressed in mathemat-
ical form. Refinements allow the expression of the classical divide-and-conquer
methodology for system design in a precise notation, which can be used for
abstraction, validation, and verification of the system at any given stage in
the development process.
Abstract state machines can be divided into two main categories, namely
basic ASMs and multiagent ASMs. The former express the behavior of a
system within a given environment. Multiagent ASMs express the behavior
of the system in terms of multiple entities that are collaborating to achieve
a functionality. For the description of the behavior of a single party, we are
interested only in basic ASMs.
A basic ASM is defined in terms of a state signature plus a finite set of
transition rules, which are executed in parallel. It may involve nondetermin-
istic behavior. Finite state machines can be viewed as a special case of such
basic ASMs. The state signature for a classical ASM usually consists simply
of a set of static and dynamic functions, which can be locally updated by
update rules. Dynamic functions can be classified into four other categories,
namely,
controlled
,
monitored
(or
in
),
interaction
(or
shared
), and
out
.Con-
trolled functions are directly updatable by the rules of a machine
M
only.
Thus, they can be neither read nor updated by the environment. Monitored
functions can only be updated by the environment and read by the machine
M
, and hence constitute the externally controlled part of the state. Shared
functions can be read and updated by both the environment and the rules of
the machine
M
. Out functions can be updated and read by the environment,
but remain unreadable by
M
. Furthermore, ASMs define
derived functions
.
These are functions that are updatable by neither the machine nor the envi-
ronment but are instead defined in terms of other static and dynamic (and
derived) functions.
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