Semantic Annotation for Process Models: - Department of Computer ...

54 CHAPTER 3. STATE OF THE ART
Ontologies referenced in the annotation are modeled in DAML, RDF-S, or OWL.
WSDL descriptions use XML Schema to provide the basic structure of the data to be
exchanged by Web services. Hence, a SchemaGraph is used as a common representation
format to facilitate the match between an ontology model and a XML Schema.
Through the SchemaGraph, pairs of comparable concepts from the ontology model and
WSDL descriptions are found. The semi-automatic annotation of MWSAF is accomplished
through Element Level Match and Schema Level Match between the comparable
ontology concepts and WSDL concepts. The element level match is the measure of the
linguistic similarity between two concepts based on their names. Some NLP techniques
are applied in the element level match, such as NGram, synonym matching,
abbreviation expansion, stemming, tokenization, etc. [159]. The schema level match is
the measure of structural similarity between two concepts. The structural similarity
is calculated by the geometric mean of sub-concept similiary and sub-concept match.
Sub-concepts of an ontology concept are the property concepts of the ontology class,
while sub-concepts of WSDL descriptions are the elements of a "complexType" entity
in the XML Schema. A ranking mechanism to find the best matching is employed after
a WSDL concept has been compared against all the concepts from the ontology.
3.4.6 SAWSDL (Semantic Annotations for WSDL and XML Schema)
SAWSDL [201] as a W3C recommendation is aimed to provide an annotation mechanism
to add semantics to WSDL descriptions and XML Schemas. The annotation mechanism
is accomplished through the extension attributes of WSDL and XML Schema
elements to reference concepts from semantic models. A semantic model could be any
machine-interpretable representations about an area of knowledge or some parts of the
world, e.g. ontologies or mapping documents. The extension attributes fit within the
WSDL 2.0, WSDL 1.1 and XML Schema, so that the annotations are embedded in
WSDL files and XML Schema. The semantic annotation results are supposed to be
used in the Web service publishing, discovery and composition. Moreover, the data
mapping of XML Schema types to and from an ontology by the annotation can be used
for invocation.
SAWSDL defines the extension attributes modelReference, liftingSchemaMapping
and loweringSchemaMapping. The first one is used to annotate a concept in
some semantic model to a WSDL or XML Schema component. The component include
XML Schema type definitions, element declarations, attribute declarations as
well as WSDL interfaces, operations, and faults. The latter two are added to XML
Schema element declarations and type definitions for specifying the URIs that reference
mapping definitions. liftingSchemaMapping defines how an XML instance in a
schema is transformed to data in a semantic model. Reversely, loweringSchemaMapping
denotes how data in a semantic model is transformed to XML instance data
[201]. The annotation attributes have prefix "sawsdl", e.g. sawsdl:modelReferece,
sawsdl:liftingSchemaMapping.
In the SAWSDL specification, multiple semantic annotations are allowed to be
associated with WSDL elements. No restriction is made on the ontology expression
language and mapping languages.