Introduction

OWL-S API provides a Java API for programmatic access to create, read, write, and execute OWL-S (formerly known as DAML-S) described atomic as well as composite services.

The library provides a basic ProcessExecutionEngine that can execute atomic processes (a.k.a. atomic service) using WSDL, Java, or UPnP groundings, and composite processes (a.k.a. composite service) that use control constructs such as Choice, Sequence, AnyOrder, Split, and Split-Join. Execution of processes that consist of conditional control constructs such as IfThenElse, RepeatUntil, or RepeatWhile is also supported. Furthermore, execution of processes can be monitored by means of ProcessExecutionMonitor.

Languages that are supported to express conditions (for specifying conditional control constructs as well as process preconditions) are SWRL and SPARQL. The API is designed to be extensible so that other (logical) formalisms can be integrated, which come with their own evaluation procedure. The API is distributed together with the OWL-DL reasoner Pellet. Other reasoners can be integrated, see subsequent section about Jena.

The class structure of the API has been designed to closely match the definitions of OWL-S ontologies, specifically OWL-S version 1.2 and 1.1. The names for packages, interfaces and methods in Java are chosen to match the names of ontologies, classes and properties in OWL-S ontologies. There are some exceptions to this rule where simpler or more descriptive names are chosen to make programming easier. For example, the method in Service class to get the associated Profile is named as getProfile rather than getPresents as the property name service:presents in OWL-S ontology suggests.

Furthermore, the API provides almost complete support for standard RDF and OWL management tasks such as adding, removing and querying triples. The basic Java abstractions provided (which are extended by all OWL-S specific abstractions) are OWLObject, OWLEntity, and OWLIndividual. They come with access methods to get the value of any OWL property (no matter if annotation, object, or data property). It is also possible to access the underlying data model (which is based on Jena right now). However, the underlying data model is not statically accessible from the API interfaces (i.e., casts are required for accessing the Jena model or resources), because one design goal of the API was to be agnostic regarding underlying OWL libraries so that they may be exchanged, for instance, by the OWL API. Finally, all reasoner implementations that provide integration with Jena can be used.

OWL-S Version Conformance

As of the 3.x codeline, the API supports OWL-S version 1.2 by default. The previous 2.x codeline supports OWL-S 1.1 by default. Services described using OWL-S 1.0 can be automatically translated to OWL-S 1.1. Note that support for OWL-S 1.1 and 1.0 has been deprecated. The translation mechanism is currently not actively maintained. Support for version 1.0 and 1.1 may be removed completely in the future.

Limitations

  • Support for SWRL built-in atoms is not completely implemented. The following built-ins are supported: equal, notEqual, lessThan, lessThanOrEqual, greaterThan, greaterThanOrEqual, add, subtract, multiply, divide.

Acknowledgments

OWL-S API was originally developed and maintained by the mindswap group in collaboration with Fujitsu Labs of America, College Park. Its development and maintenance is continued as part of the OSIRIS Next open service infrastructure project at University of Basel by Thorsten Möller, Database and Information Systems Group.

Mailing List

You may still subscribe and send your questions and comments to the OWL-S mailing list on mindswap and see the archives here.