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OWL-S: Semantic Markup for Web Services

Baryannis George, METTesseris 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

Control flow of the service Service viewed as a process Data Flow Parameter bindings

Mapping from abstract to concrete (e.g. OWL-S to WSDL)

Inputs/Outputs to Messages Atomic processes to

operations

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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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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Service Profile In Detail (2/6)

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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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Service Profile In Detail (4/6)

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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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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., 2004 http://www.daml.org/services/owl-s/1.1/

OWL-S: Semantic Markup for Web Services v1.2 Prerelease, David Martin et al., 2006 http://www.ai.sri.com/daml/services/owl-s/1.2/

Web Service Description Languages, Presentation and report, George Tesseris