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WSMO Choreography Model
WSMO choreography deals with the interactions of the Web service from
the client's perspective. We base the description of the behavior of a single
service exposed to its client on the basic ASM model. WSMO choreography
interface descriptions inherit the core principles of such ASMs, which can be
summarized as follows: (1) they are state-based, (2) they represent a state by
a signature, and (3) they model state changes by transition rules that change
the values of functions and relations defined by the signature of the algebra
(which, in our context, is a nonempty set of ontologies).
In order to define the signature we use a WSMO ontology, i.e. definitions
of concepts, their attributes, and relations and axioms over these. Instead of
dynamic changes of function values as represented by dynamic functions in
ASMs, we allow the dynamic modification of instances and attribute values in
the state ontology. Note that the choreography interface describes the interac-
tion with respect to a single instance of the choreography. The key extension
compared with the basic ASMs described above is that the machine signature
is defined in terms of a WSMO ontology (or possibly more than one), and the
logical language used for expressing conditions is WSML. This leads us to the
notion of evolving ontologies (derived from the notion of evolving algebras, the
name initially used for ASMs), since the choreography ASM in fact changes
the values of concepts and relations within ontologies.
Taking the ASM methodology as a starting point, a WSMO choreography
consists of three elements, which are defined as follows:
Class
choreography
hasNonFunctionalProperties
type
nonFunctionalProperties
hasStateSignature
type
stateSignature
hasTransitionRules
type
transitionRules
The set of
nonfunctional properties
that can be attached to a capability is
presented in Section 6.5. The
state signature
defines the state ontology used
by the service, together with the definition of the types of modes that the
concepts and relations may have.
State Signature
The signature of the machine is defined by (1) importing an ontology which
defines the state signature over which the transition rules are executed, (2) an
optional set of OO mediators if the imported state ontologies are heterogenous,
(3) a set of statements defining the modes of the concepts and relations, and
(4) a set of update functions. The default mode for concepts of the imported
ontologies which are not listed explicitly in the mode statements is static.
Note it is not allowed to assign either “in” or “out” to concepts which have
explicitly defined any instance data in the imported ontologies by the state
signature. The definition of the state signature is expressed as follows:
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