Validation
The most common reasoner operation which can't be exposed through additional triples in the inference model is that of validation. Typically the ontology languages used with the semantic web allow constraints to be expressed, the validation interface is used to detect when such constraints are violated by some data set.
A simple but typical example is that of datatype ranges in RDFS. RDFS allows us to specify the range of a property as lying within the value space of some datatype. If an RDF statement asserts an object value for that property which lies outside the given value space there is an inconsistency.
To test for inconsistencies with a data set using a reasoner we use the InfModel.validate() interface. This performs a global check across the schema and instance data looking for inconsistencies. The result is a ValidityReport object which comprises a simple pass/fail flag (ValidityReport.isValid()) together with a list of specific reports (instances of the ValidityReport.Report interface) which detail any detected inconsistencies. At a minimum the individual reports should be printable descriptions of the problem but they can also contain an arbitrary reasoner-specific object which can be used to pass additional information which can be used for programmatic handling of the violations.
For example, to check a data set and list any problems one could do something like:
Model data = FileManager.get().loadModel(fname);
InfModel infmodel = ModelFactory.createRDFSModel(data);
ValidityReport validity = infmodel.validate();
if (validity.isValid()) {
System.out.println("OK");
} else {
System.out.println("Conflicts");
for (Iterator i = validity.getReports(); i.hasNext(); ) {
System.out.println(" - " + i.next());
}
}
The file testing/reasoners/rdfs/dttest2.nt declares a property bar with range xsd:integer and attaches a bar value to some resource with the value "25.5"^^xsd:decimal. If we run the above sample code on this file we see:
Conflicts
- Error (dtRange): Property http://www.hpl.hp.com/semweb/2003/eg#bar has a typed range Datatype[http://www.w3.org/2001/XMLSchema#integer -> class java.math.BigInteger]that is not compatible with 25.5:http://www.w3.org/2001/XMLSchema#decimal
Whereas the file testing/reasoners/rdfs/dttest3.nt uses the value "25"^^xsd:decimal instead, which is a valid integer and so passes.
Note that the individual validation records can include warnings as well as errors. A warning does not affect the overall isValid() status but may indicate some issue the application may wish to be aware of. For example, it would be possible to develop a modification to the RDFS reasoner which warned about use of a property on a resource that is not explicitly declared to have the type of the domain of the property.
A particular case of this arises in the case of OWL. In the Description Logic community a class which cannot have an instance is regarded as "inconsistent". That term is used because it generally arises from an error in the ontology. However, it is not a logical inconsistency - i.e. something giving rise to a contradiction. Having an instance of such a class is, clearly a logical error. In the Jena 2.2 release we clarified the semantics of isValid(). An ontology which is logically consistent but contains empty classes is regarded as valid (that is isValid() is false only if there is a logical inconsistency). Class expressions which cannot be instantiated are treated as warnings rather than errors. To make it easier to test for this case there is an additional method Report.isClean() which returns true if the ontology is both valid (logically consistent) and generated no warnings (such as inconsistent classes).
[返回] 中文XML论坛 - 专业的XML技术讨论区 →
W3CHINA.ORG讨论区 - Web新技术讨论 → 『 Semantic Web(语义Web)/描述逻辑/本体 』 → 检查本体一致性
(订阅本版)
2008/7/17 11:39:00
新浪微博
检查本体一致性
