TY - JOUR
T1 - A new mechanism for exception handling in concurrent control systems.
AU - Beek, van, D.A.
AU - Rooda, J.E.
PY - 1996
Y1 - 1996
N2 - The most difficult aspect of concurrent discrete-event control is the handling of errors.
Most present day languages for concurrent control system specification do not provide
adequate mechanisms for exception handling, which is a major limitation on their effectiveness.
In this paper, a new mechanism for exception handling in concurrently executing discrete-event control processes is treated, which simplifies the complex task of robust control system specification. The mechanism is based on constraint monitors, and can be used in conjunction with known mechanisms for exception handling in sequential programs.
Constraints and constraint monitors are new concepts which are essential for dealing
with exceptions in control systems. The constraints of a statement are conditions which
must be valid throughout the execution of the statement. Constraint monitors are used
to specify the constraints of a statement in a structured way, leading to programs in
which the code for normal operation is separated from the code for exception handling.
During the execution of the statement, the specified constraints are monitored at all
encountered interaction points. If a constraint violation is detected, an exception is
raised.
In this way, the invariants of a process remain valid, finalization obligations of statements
are executed, deadlock in the case of exception occurrences is prevented, and
exceptions are not raised in processes in which no constraints have been violated. Constraint monitors are explained using a CSP-like language to which exception handling
constructs have been added. The constructs have been chosen in such a way, that the
resulting syntax and semantics are simple and especially suitable for the specification
of robust control systems. The mechanism is finally illustrated by an example of the
specification of a control system.
AB - The most difficult aspect of concurrent discrete-event control is the handling of errors.
Most present day languages for concurrent control system specification do not provide
adequate mechanisms for exception handling, which is a major limitation on their effectiveness.
In this paper, a new mechanism for exception handling in concurrently executing discrete-event control processes is treated, which simplifies the complex task of robust control system specification. The mechanism is based on constraint monitors, and can be used in conjunction with known mechanisms for exception handling in sequential programs.
Constraints and constraint monitors are new concepts which are essential for dealing
with exceptions in control systems. The constraints of a statement are conditions which
must be valid throughout the execution of the statement. Constraint monitors are used
to specify the constraints of a statement in a structured way, leading to programs in
which the code for normal operation is separated from the code for exception handling.
During the execution of the statement, the specified constraints are monitored at all
encountered interaction points. If a constraint violation is detected, an exception is
raised.
In this way, the invariants of a process remain valid, finalization obligations of statements
are executed, deadlock in the case of exception occurrences is prevented, and
exceptions are not raised in processes in which no constraints have been violated. Constraint monitors are explained using a CSP-like language to which exception handling
constructs have been added. The constructs have been chosen in such a way, that the
resulting syntax and semantics are simple and especially suitable for the specification
of robust control systems. The mechanism is finally illustrated by an example of the
specification of a control system.
U2 - 10.1016/S0947-3580(96)70033-X
DO - 10.1016/S0947-3580(96)70033-X
M3 - Article
VL - 2
SP - 88
EP - 100
JO - European Journal of Control
JF - European Journal of Control
SN - 0947-3580
ER -