Information Technology Reference
In-Depth Information
Services as a Paradigm of Computation
Wolfgang Reisig, Jan Bretschneider, Dirk Fahland, Niels Lohmann,
Peter Massuthe, and Christian Stahl
Humboldt-Universitat zu Berlin, Institut fur Informatik
Unter den Linden 6, 10099 Berlin, Germany
{ reisig,bretschn,fahland,nlohmann,massuthe,stahl } @informatik.hu-berlin.de
Abstract. The recent success of service-oriented architectures gives rise
to some fundamental questions: To what extent do services constitute a
new paradigm of computation? What are the elementary ingredients of
this paradigm? What are adequate notions of semantics, composition,
equivalence? How can services be modeled and analyzed? This paper
addresses and answers those questions, thus preparing the ground for
forthcoming software design techniques.
Keyword: models of computation, services, SOA, open workflow nets.
1
The Demand for a New Paradigm of Computation
1.1
Shortcomings of the Classical Paradigm
The classical paradigm of computation characterizes the behavior of an infor-
mation processing system as a function, f : A user of the system supplies an
argument x and expects to eventually receive the result f ( x )fromthesystem.
Experience with distributed and reactive systems reveals the need for a more
comprehensive paradigm. Among the many arguments for a new paradigm, the
following may be the most striking one: A computation of a system does not nec-
essarily receive all its input in the initial state, nor does it withheld all its output
until it reaches a final state. Rather, a computation may start running with no
or a first portion of input, and it may provide output whenever generated. In
short, a computation may exchange messages with the systems' environment
during its course. Examples of such systems include operating systems, any kind
of technical control systems, and many forms of co-operating business processes.
It is not too dicult to capture this kind of behavior in the framework of con-
ventional programming, establishing communication of a program P with its
environment by help of special input and output procedures, variables shared
by P and its environment, and remote procedure calls. It took decades to ac-
knowledge that this property of computations is not just a minor aspect, but
that it affects (among other aspects, to be discussed elsewhere) our fundamental
understanding of computation.
Search WWH ::




Custom Search