Ratio4TA Vocabulary Specification

Abstract

The Semantic Web applications produce ever changing interlinked data. The applications that utilize these data to obtain their results should provide explanations about how the results are obtained in order to ensure the effectiveness and increase the user acceptance of these applications. Justifications providing meta information about why a conclusion has been reached enable generation of such explanations. Ratio4TA (interlinked justifications for triple assertions) is a lightweight vocabulary for encoding justifications using named graphs.

The figure below shows the classes and properties ofRatio4TA.

Introduction

Justifications are generated by the reasoners that are distributed across the Web. Therefore, the related justifications distributed across the Web should have the possibility to express their relation. The Ratio4TA vocabulary allows explicitly expressing the antecedent dependency between justifications. The consumers of the justifications can determine the triples from which a given triple is inferred by exploiting the link structure of the linked justifications. In essence, linking justifications allow maintenance of related facts and justifications in a distributed setting.

Ratio4TA defines the Assertion class and the Justification class as named graphs by extending the rdfg:Graph class. An Assertion named graph contains an asserted triple. This allows making statements about the triple by referencing to the triple using the named graph identifier. A Justification named graph contains a group of triples that justify the assertion of a triple.

We use r4ta as the namespace prefix for the terms of Ratio4TA throughout this document.

Example

Here is an example justifying the assertion of a triple:

#graph for a triple 
aloc:t1 { 
    AcadWiki:Bob AcadWiki:birthPlace GeoWiki:UnitedKingdom.
}

#graph justifying the assertion of a triple 
aloc:j1 {
    aloc:j1 rdf:type Justification;
            r4ta:justifies aloc:t1;
            r4ta:antecedent AcadWiki:j4;
            r4ta:antecedent GeoWiki:j1.
    aloc:t1 rdf:type r4ta:InferredAssertion.
    aloc:t1 r4ta:inferredByRule aloc:pobRule.
}

Ratio4TA Description

Classes

Class: r4ta:Assertion

Represents an asserted triple.

Subclass Of	`rdfg:Graph`
In Range Of	`r4ta:justifies`

Class: r4ta:DirectAssertion

Represents a directly asserted triple that represents a ground facts.

Subclass Of	`r4ta:Assertion`

Class: r4ta:InferredAssertion

Represents an asserted triple that is inferred from other triples.

Subclass Of	`r4ta:Assertion`
In Domain Of	`r4ta:inferredByRule`

Class: r4ta:Justification

Represents a justification.

Subclass Of	`rdfg:Graph`
In Domain Of	`r4ta:justifies`, `r4ta:antecedent`
In Range Of	`r4ta:antecedent`

Class: r4ta:InferenceRule

Represents an inference rule that has been enforced to infer a triple. How rules will be encoded are not restricted to a particular encoding on purpose to accommodate different kinds of rule based systems distributed across the Web.

In Range Of	`r4ta:inferredByRule`

Properties

Property: r4ta:antecedent

The property associates a r4ta:Justification to an antecedent r4ta:Justification.

Domain:	`r4ta:Justification`
Range:	`r4ta:Justification`

Property: r4ta:inferredByRule

The property associates a r4ta:InferredAssertion to a r4ta:InferenceRule.

Domain:	`r4ta:InferredAssertion`
Range:	`r4ta:InferenceRule`

Property: r4ta:justifies

The property associates an r4ta:Justification to a r4ta:Assertion

Domain:	`r4ta:Justification`
Range:	`r4ta:Assertion`

External Classes and Properties

Classes: rdfg:Graph

Ratio4TA Vocabulary Specification 0.1

Namespace Document 6 February 2012