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AI-Trader
Introduction
The continuous merging of numerous local computer
networks has resulted in an open distributed system. In this
environment services are freely offered and requested. New service
providers are constantly emerging and advertising their products in
this electronic market place, while others are leaving the system. The
resulting fluctuation of service offers adds to the complexity of an
open distributed system. It is impossible for a user to gain a
complete overview of the services currently offered. The dynamics and
size of such an environment implies, that the knowledge about its
structure decreases proportional with the increase in time.
Several institutions work on technology
independent standards which define frameworks for open distributed
systems. For example the International Organization for
Standardization (ISO) and the International Telecommunication
Union, Telecommunication Standardization Sector (ITU-T) have
developed the Reference Model for Open Distributed Processing
(RM-ODP). The RM-ODP describes an architecture which supports the
distribution, interoperability and portability of software components.
Furthermore the RM-ODP demands the support of a trading
function which assists in the search for services. All
participating parties in an open distributed system assume the roles
of service providers and service requesters, which
have no a priori knowledge about each other. In particular
they are not linked statically to each other, but rather dynamically
when the need arises.
In the RM-ODP the trading of services is based on
a mediation process. During the mediation of services another
party assumes the role of a trader, whose task is to match
service offers and requests (see Figure 1). According to the RM-ODP a
mediation process is divided into several steps. First a service
provider exports its service offer with the trader. At a later point
in time a service requester tries to import a particular service. If
the trader finds a matching service offer, which has previously been
exported, it responds a reference to the service requester pointing to
the appropriate provider. After a successful mediation process the
service requester and provider are bound to each other and start to
interact.
Figure 1: RM-ODP trader model
The notion of a type system is essential
for the discussion of a mediation process. For one thing a type system
defines a type specification language, which allows the specification
of services in open distributed systems. Furthermore a type system
defines rules, which allow the association of service offer and
request, both represented as type specifications. The type
specification language of the RM-ODP focuses on operational aspects of
a type specification, i.e. how a service is accessible from a
programming point of view. Within a global system, where programmers
as well as application users are exposed to the mediation process, the
selection of type specifications is of equal importance. This
emphasizes the need for semantic service type specifications, which
allow the description of services with identical operational
interfaces but different qualitative characteristics.
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