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method will be presented to the teacher as main result, and the results of the other methods
will be presented as an alternative. Another feature of this agent will be also to provide
actual statistics on the performance of each of the calculating methods, as the "weakest'' of
them goes out of service until new and better performing methods are added to the
Evaluator agent. This monitoring of the methods' behavior becomes really significant when
the so-called genetic algorithms are added, which we are still working on - as it is known,
they can be "trained'' and thus their effectiveness can change. In this process a knowledge
base is developing for each specific subject, which supports the methods in their work.
5. Calculus of context aware systems - CCA
Context-awareness requires applications to be able to adapt themselves to the environment
in which they are being used such as user, location, nearby people and devices, and user's
social situations. In this section we use small examples to illustrate the ability of CCA to
model applications that are contextaware.
5.1 Syntax of processes and capabilities
This section introduces the syntax of the language of CCA. Like in the π-calculus
[Milner,1999], [Sangiorgi,2001], the simplest entities of the calculus are names . These areused
to name for example ambients, locations, resources and sensors data. We assume a
countably-infnite set of names, elements of which are written in lower-case letters, e.g. n, x
and y . We let denote a list of names and || the arity of such a list. We sometimes use as a
set of names where it is appropriate. We distinguish three main syntactic categories:
processes P , capabilities M and context expressions κ .
The syntax of processes and capabilities is given in Table 1 where P , Q and R stand for
processes, and M for capabilities. The first five process primitives (inactivity, parallel
composition, name restriction, ambient and replication) are inherited from MA
[Cardelli,2000]. The process 0 does nothing and terminates immediately. The process P | Q
denotes the process P and the process Q running in parallel. The process ( υn ) P states that
the scope of the name n is limited to the process P . The replication ! P denotes a process
which can always create a new copy of P . Replication was first introduced by Milner in the
π-calculus [Milner,1999]. The process n [ P ] denotes an ambient named n whose behaviours
are described by the process P . The pair of square brackets `[' and `]' outlines the boundary
of that ambient. This is the textual representation of an ambient. The graphical
representation of that ambient is:
The graphical representation highlights the nested structure of ambients.
CCA departs from MA and other processes calculi such as [Zimmer,2005], [Bucur,2008],
[Bugliesi,2004] with the notion of context-guarded capabilities , whereby a capability is guarded
by a context-expression which specifes the condition that must be met by the environment
of the executing process. A process prefxed with a context-guarded capability is called a
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