1. OWL-S: Semantic Markup for Web Services
Baryannis George, MET
Tesseris George, MET
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OWL-S
Stands for Web Ontology Language for Services
An OWL ontology/language to formally describe Web services
Began as part of the DARPA DAML project, formerly known as DAML-S
Currently in version 1.1 / 1.2 Prerelease
WSDL supports only syntactic web service descriptions
Only syntactic support for discovery, invocation and composition
Web Service usage and integration needs to be supported manually
OWL-S provides a semantic layer for web service description using ontologies
Ontologies provide machine-understandable semantics
Semantics deals with meaning/content
More effective web service discovery, invocation, composition and interoperation
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OWL-S Upper Ontology
Capabilities description
Service requirements
Quality of Service
Classification in Service taxonomies
Mapping from abstract to concrete (e.g. OWL-S to WSDL)
Inputs/Outputs to Messages
Atomic processes to operations
Control flow of the service
Service viewed as a process
Data Flow
Parameter bindings
Cardinality constraints
Service described by at most one ServiceModel
ServiceGrounding associated by exactly one Service
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Service Profile
Service Profile
Provider information
contact information
Functional description
inputs and outputs
preconditions and effects
Service features
Category and QoS
Unbounded list of parameters (max response time, geographic availability etc.)
Two main uses:
Advertisement of Web Services capabilities (non-functional properties, QoS, Description, classification, etc.)
Request of Web services with a given set of capabilities
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Service Model
Service Model
Describes how a service works: internal processes of the service in addition to inputs, outputs, preconditions and results
Three types of processes:
Atomic: single interaction, directly invokable
Composite: decomposable into other processes (composite or not)
Simple: either abstract views of atomic processes or simplified views of composite processes
Defines the control structure of composite processes
Sequence, Split, Split+Join, Any-Order, Choice, If-Then-Else, Iterate, Repeat-While, Repeat-Until
Facilitates
Web service invocation
Composition of Web services
Monitoring of interaction
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Service Grounding
Service Grounding
Specifies how to access the service (protocol and message formats, serialization, transport and addressing)
Service Model + Grounding give everything needed for using the service
One possible grounding approach is to build upon WSDL to define message structure and physical binding layer
WsdlGrounding subclass that maps to specific elements in the WSDL specification such as operations, ports and messages
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7. Service Profile In Detail (1/6)
serviceName
A name for the service that can be used as an identifier
textDescription
A brief description of the service (what the service offers, what it requires etc.)
contactInformation
provides a mechanism of referring to individuals responsible for the service. The range of this property is unspecified within OWL-S, but can be restricted to some other ontology (e.g. Actor class)
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8. Service Profile In Detail (2/6)
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9. Service Profile In Detail (3/6)
hasParameter
ranges over a Parameter instance of the Process ontology. Inputs and Outputs are kinds of Parameters
hasInput
specifies one of the inputs of the service
hasOutput
specifies one of the outputs of the service
hasPrecondition
specifies one of the
preconditions of the service
hasResult
specifies one of the results
of the service. It specifies
under what conditions the
outputs are generated
(postconditions). Also, the
Result specifies what domain
changes are produced
during the execution of the
service. (effects)
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10. Service Profile In Detail (4/6)
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11. Service Profile In Detail (5/6)
serviceParameter
an expandable list of properties, instances of the class ServiceParameter.
serviceParameterName: the name of the actual parameter
sParameter: points to the value of the parameter within some OWL ontology.
serviceCategory
refers to an entry in some ontology or taxonomy of services. Instance of the class ServiceCategory
categoryName: the name of the actual category
taxonomy: a reference to the taxonomy scheme.
value: points to the value in a specific taxonomy
code: code associated to a taxonomy.
serviceClassification
defines a mapping from a Profile to an OWL ontology of services (NAICS specification)
serviceProduct
defines a mapping from a Profile to an OWL ontology of products (UNSPSC specification)
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12. Service Profile In Detail (6/6)
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Why OWL instead of RDFS
The goal behind OWL-S is for web sites to be able to employ a standard ontology for declaring and describing services
The authors state that “the ontology structuring mechanisms of OWL provide an appropriate, Web-compatible representation language framework” that allows them to achieve their goal
Some OWL characteristics that were necessary for OWL-S are:
Cardinality constraints
Classes expressions involving unionOf, disjointUnionOf, intersectionOf, or complementOf
Inference: constructs such as inverseOf, and disjointWith are used in the declaration of properties
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References
OWL-S: Semantic Markup for Web Services v1.1, David Martin et al.,
OWL-S: Semantic Markup for Web Services v1.2 Prerelease, David Martin et al.,
Web Service Description Languages, Presentation and report, George Tesseris
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