This paper presents a Web-based environment for visualising and manipulating multiple ontology alignments at schema-level. While most solutions are limited to the visualisation of single alignments and are still provided as part of speci c standalone matching systems, we propose an open environment that is not bound to any speci c system. Within this graphical environment, users can manually create, suppress and edit correspondences and apply a set of operations on alignments ( ltering, merge, di erence, etc.). Evaluating multiple alignments, against a reference one, can also be carried out using classical evaluation metrics. In this demo, all these tasks will be demonstrated.
Ontology matching has become an essential task in the management of the
semantic heterogeneity problem in open environments. Diverse matching
approaches have been proposed in the literature [
In this paper, we present an extended version1 of VOAR (Visual Ontology
Alignment EnviRonment) [
The matching process takes two ontologies o and o0 as input and generates,
as output, a set of correspondences (i.e., an alignment) between them. Each
correspondence expresses the relation r (e.g., , w, etc.) between the entities e
and e0, with a con dence in the fact that the relation holds, typically in the [
One important aspect in alignment visualisation refers to the visualisation
of the ontologies themselves. VOAR adopts a commonly used technique that
consists in presenting the ontologies as indented trees, where indentation
represents the hierarchical relations between concepts (concepts and their
subconcepts can be expanded and retracted, in order to adjust the detail of information
shown). Although this kind of technique has advantages and disadvantages [
VOAR has been developed on the top of well-know and largely used APIs in the eld of ontology matching, such as the Alignment API4 and the OWL API5, and it is built with JavaServer Faces (JSF) technology, compatible with most current browsers. Alignments in VOAR can be manipulated through four main modules, which are brie y presented in the following.
Correspondence edition This module allows for manipulating the correspondences from one single working alignment. They can be added, suppressed or edited (e.g, the kind of relation or con dence can be modi ed). The user can select speci c ontology entities for visualising the correspondences involving them. A new correspondence can be created by selecting entities in both ontologies. In each tree, users can also lter out the entities whose naming and annotations (labels, comments) correspond to a search criteria, what is especially useful when dealing with large ontologies.
Alignment manipulation VOAR provides di erent ways for manipulating a single alignment as an `object', which can be combined together with other `objects'. The current set of available operations are: union (resulting in the merge
3 Here, we focus on the visualisation of concept hierarchies and alternative ways for visualising whole ontologies are being considered.
A GUI for visualising and manipulating multiple ontology alignments of alignments), intersection (where only correspondences occurring in all input alignments are kept), di erence (complement, where a subset of correspondences are removed from a given alignment). Auxiliary operations involve the possibility to trim correspondences under a given threshold and invert the direction of the alignment. These operations are available in the Alignment API and Alignment Server for a pair of alignments, in their native versions, and we have reused them here through the Alignment API. In VOAR, users can select multiple alignments at once and apply those operations on the current working alignment. Alignment evaluation Users can compare multiple alignments with respect to a reference alignment. Measures of precision, recall, and F-measure can be computed for each alignment. The implementations available in the Alignment API have been used for generating these evaluation metrics. VOAR allows the visualisation of the results in a tabular view and displays the status of each correspondence (true negative, false negative, true positive and true negative) through icons representing the entities involved in the given correspondence.
Alignment visualisation From a set of previously loaded or manually created alignments, this module allows for visualising multiple alignments together. The set of correspondences of a given alignment is represented by a di erent line colour. The user is able to con gure the properties of the correspondences to be shown (e.g., kind of relation and con dence threshold) and apply lters on those properties in order to visualise a subset of correspondences. Figure 1 presents the screenshot of the visualisation of three alignments generated by OAEI systems (Aroma, LogMap and RiMOM) on the real Benchmark test case 3046.
This paper has presented an extended version of VOAR, a web-based
environment for visualising and manipulating ontology alignments at schema level. The
major contribution of this new version is the possibility of visualising multiple
alignments together. It allows for better comparing and analysing alignments
(i.e., parts of the ontologies which are covered for most alignments and those
which are not, consensus between alignments, etc.). As future work, we plan to
take into account the visualisation of properties and entities at instance-level.
We intend as well to provide an evaluation on its usability. Finally, we plan to
deal with the scalability of VOAR in terms of the visualisation of large
ontologies and to evaluate how it satis es a set of requirements [