Web Ontology Language for Service OWLS Introduction OWLS

Web Ontology Language for Service (OWL-S)

Introduction • OWL-S – OWL-based Web service ontology – a core set of markup language constructs for describing Web services in unambiguous, computer-interpretable form

Tasks that OWL-S is expected to enable – Automatic Web service discovery • Automated location of web services that provides a particular service and adhere to requested constraints – Automatic Web service invocation • Automated execution of an identified web service by a computer program or agent – Automatic Web service composition and interoperation • Automatic selection, composition and interoperation of web services to perform some task

Three essential types of knowledge about a service 1. What does the service provide for prospective clients? • The answer to this question is given in the "profile" which is used to advertise the service. • To capture this perspective, each instance of the class Service presents a Service. Profile.

2. How is it used? • The answer to this question is given in the "process model“(also known as “service model”) • This perspective is captured by the Service. Model class. • Instances of the class (called Service class) use the property described. By to refer to the service's Service. Model.

3. How does one interact with it? • The answer to this question is given in the "grounding“ • A grounding provides the needed details about transport protocols. • Instances of the class Service have a supports property referring to a Service. Grounding

Three essential type of knowledge about a service

Service Profile • Describes services capabilities • Describes the services offered by the providers, and the services needed by the requesters.

Three basic types of information 1. What organization provides the service • Contact information that refers to the entity that provides the service

2. What function the service computes • Specified in terms of: – Inputs required by the service and outputs generated – Preconditions required by the service and expected effects that result from the execution of the service

3. A host of features that specify characteristics of the service • The category of a given service • The quality rating of the service (some services may be very good, reliable, and quick to respond) • An unbounded list of service parameters that can contain any type of information

1 2 3 Three types of information in Service Profile

Process Model • A process is intended as a specification of the ways a client may interact with a service • A process can have two sorts of purpose: – It can generate and return some new information. • Information production is described by the inputs and outputs of the process. – It can produce a change in the environment. • This transition is described by the preconditions (which must all hold in order for the process to be successfully invoked) and effects of the process

Inputs, Outputs Preconditions and Effects (IOPE) • Inputs – specify the information that the process requires for its execution. • Outputs – produced by the invocation of a process flow back to the client as a single message. • Preconditions – a condition that must be true just before to the execution of process. • Effects – describe conditions about the environment after process be executed.

Simple process • Simple processes are used as elements of abstraction. – A simple process may be used to provide: • The simple process is realized. By the atomic process – A simplified representation of some composite process • The simple process expands. To the composite process • Simple processes are not invocable (not associated with a grounding)

Atomic process • An atomic process corresponds to the behavior a service can perform. – Expects one message and returns one message in response. • Atomic processes are directly invocable (associated with a grounding) • Atomic processes have no sub-processes and execute in a single step.

Composite process • Composite processes are decomposable into other non-composite or composite processes • Their decomposition can be specified by using control constructs (next page) • A composite process is not a behavior of a service, but a set of behaviors the client can invoke by sending messages and receiving results.

Control Constructs • Sequence – A list of control constructs to be done in order. • Split – A bag of process components to be executed concurrently. Split completes as soon as all of its component processes have been scheduled for execution. • Split-Join – The process consists of concurrent execution of a bunch of process components with barrier synchronization. Split+Join completes when all of its components processes have completed.

• Any-Order – Allows the process components (specified as a bag) to be executed in some unspecified order but not concurrently. Execution and completion of all components is required. • Choice – Execution of a single control construct from a given bag of control constructs. Any of the given control constructs may be chosen for execution • If-Then-Else – Conditionally executes process components , depending on the value of a conditional expression.

• Iterate – Is an "abstract" class, serves as the common superclass of Repeat-While, Repeat-Until, and potentially other specific iteration constructs. • Repeat-While and Repeat-Until – Iterate until a condition becomes false or true, following the familiar programming language conventions.

Process Model

Service Grounding • Providing details on how to interoperate/access the service – Protocol, message formats, serialization, … – A mapping from an abstract specification to a concrete realization • How the abstract inputs and outputs of an atomic process are to be realized concretely as messages (which carry these inputs and outputs) – WSDL as a possible grounding approach – Exploiting the extensibility elements of WSDL

f 1(int a, b) int a=1, b=2; e. g. f 1(1, 2) Mapping between OWL-S and WSDL

How WSDL definitions refer to corresponding OWL-S declarations • wsdl. Version: – A URI that indicates the version of WSDL in use. • wsdl. Document: – A URI of a WSDL document to which this grounding refers. • wsdl. Operation: – The URI of the WSDL operation corresponding to the given atomic process.

• wsdl. Service, wsdl. Port (optional): – The URI of a WSDL service (or port) that offers the given operation. • wsdl. Input. Message: – An object containing the URI of the WSDL message definition that carries the inputs of the given atomic process. • wsdl. Input: – An object containing a mapping pairs, for a message part of the WSDL input message. Each pair is represented using an instance of Wsdl. Input. Message. Map.

• wsdl. Output. Message: – Similar to wsdl. Input. Message, but for outputs. • wsdl. Output: – Similar to wsdl. Input, but for outputs.