publications

@inproceedings{LuTe:ASWC09,
  author    = {Lina Lubyte and Sergio Tessaris},
  title     = {Supporting the Development of Data Wrapping
               Ontologies},
  booktitle = {Proceedings of the 4th Asian Semantic Web
               Conference (ASWC 2009)},
  editor    = {Asunción Gómez-Pérez and Yong Yu and Ying Ding},
  series    = {LNCS},
  volume    = {5926},
  year      = {2009},
  pages     = {31-45},
  publisher = {Springer}
  doi       = {http://dx.doi.org/10.1007/978-3-642-10871-6_3}
}

We consider the problem of designing data wrapping ontologies whose purpose is to describe relational data sources and to provide a semantically enriched access to the underlying data. Since such ontologies must be close to the data they wrap, the new terms that they introduce must be supported by data from the relational sources; i.e. when queried, they should return nonempty answers. In order to ensure non-emptiness, those wrapping ontologies are usually carefully handcrafted by taking into account the query answering mechanism. In this paper we address the problem of supporting an ontology engineer in this task. We provide an algorithm for verifying emptiness of a term in the data wrapping ontology w.r.t. the data sources. We also show how this algorithm can be used to guide the ontology engineer in fixing potential terms unsupported by the data. Finally, we present an implemented tool and an empirical study showing benefits of our approach.

@inproceedings{LuTe:DEXA09,
  author    = {Lina Lubyte and Sergio Tessaris},
  title     = {Automatic Extraction of Ontologies 
               Wrapping Relational Data Sources},
  booktitle = {Proceedings of the 20th International Conference
               on Database and Expert Systems Applications
               (DEXA 2009)},
  editor    = {S.S. Bhowmick and J. Küng and R. Wagner},
  series    = {LNCS},
  volume    = {5690},
  year      = {2009},
  pages     = {128-142},
  publisher = {Springer}
  doi       = {http://dx.doi.org/10.1007/978-3-642-03573-9_10}
}

Describing relational data sources (i.e. databases) by means of ontologies constitutes the foundation of most of the semantic based approaches to data access and integration. In spite of the importance of the task this is mostly carried out manually and, to the best of our knowledge, not much research has been devoted to its automatisation. In this paper we introduce an automatic procedure for building ontologies starting from the integrity constraints present in the relational sources.
Our work builds upon the wide literature on database schema reverse engineering; however, we adapt these techniques to the specific purpose of reusing the extracted schemata (or ontologies) in the context of semantic data access. In particular, we ensure that the underlying data sources can be queried through the ontologies and the extracted ontologies can be used for semantic integration using recently developed techniques in this area.
In order to represent the extracted ontology we adopt a variant of the DLR-Lite description logic because of its ability to express the mostly used modelling constraints, and its nice computational properties. The connection with the relational data sources is captured by means of sound views. Moreover, the adoption of this formal language enables us to prove that the extracted ontologies preserve the semantics of the integrity constraints in the relational sources. Therefore, there is no data loss, and the extracted ontology constitutes a faithful wrapper of the relational sources.

@inproceedings{LuTe:DL08,
  author    = {Lina Lubyte and Sergio Tessaris},
  title     = {Supporting the Design of Ontologies for Data
               Access},
  booktitle = {Proceedings of the 21st International Workshop on
               Description Logics (DL 2008)},
  year      = {2008}
}

The benefits of using an ontology over relational data sources to mediate the access to these data are widely accepted and well understood. However, building such ontologies is a time consuming and error-prone process. Recently this problem has been tackled by proposing a technique for automatically wrapping the relational data sources by means of an ontology. In this paper we address the problem of supporting the ontology engineer in the task of enriching of such ontologies. In fact, changes to the ontology can be unsupported by the underlying data sources; which means that it is likely that queries against the enriched ontology return empty answers. To avoid this problem the ontology must be carefully handcrafted, and we propose a first step towards the automatic support of this task. We provide an algorithm, based on query reformulation, for verifying emptiness of a term in the enriched ontology with respect to the data sources. Moreover, we show how this algorithm can be applied to guide the user in designing meaningful wrappers.

@inproceedings{RodrLC:IIMAS08,
  author    = {Mariano Rodriguez-Muro and Lina Lubyte and
               Diego Calvanese},
  title     = {Realizing Ontology Based Data Access: A Plugin
               for Protégé},
  booktitle = {Proceedings of the Workshop on Information
               Integration Methods, Architectures, and Systems
               (IIMAS 2008), in conjunction with ICDE 2008,
               Cancún, México, April 11-12, 2008},
  year      = {2008},
  pages     = {286-289},
  ISBN      = {978-1-4244-2162-6}
  publisher = {IEEE Computer Society}
  doi       = {http://dx.doi.org/10.1109/ICDEW.2008.4498333}
}

In Ontology-Based Data Access (OBDA), the aim is to use an ontology to mediate the access to data sources. We present a plug-in for the standard ontology editor \protege that allows users to model ontologies with mappings to data sources in order to perform OBDA. We argue that our plug-in, together with an OBDA-Enabled reasoner, allows users to build, test, and deploy OBDA Systems in academic or industrial settings.

@inproceedings{Lub:PIKM07,
  author    = {Lina Lubyte},
  title     = {Reusing Relational Sources for Semantic
               Information Access},
  booktitle = {Proceedings of the First Ph.D. Workshop in CIKM,
               PIKM 2007, Sixteenth ACM Conference on Information
               and Knowledge Management, CIKM 2007, Lisbon,
               Portugal, Novermber 9, 2007},
  editor    = {Aparna S. Varde and Jian Pei},
  year      = {2007},
  pages     = {9-16}
  publisher = {ACM}
  doi       = {http://doi.acm.org/10.1145/1316874.1316877}
}

The rapid growth of available data arises the need for more sophisticated techniques for semantic access to information. It has been proved that using conceptual model or ontology over relational data sources is necessary to overcome many problems related with accessing the structured data. However, the task of wrapping the data residing in a database by means of an ontology is mainly done manually.
The research we are carrying out studies the reuse of relational sources in the context of semantics-based access to information. This problem is tackled in two phases: (i) extracting semantics hidden in the relational sources by wrapping them by means of an ontology, (ii) understanding the methodology for semantic extension of such ontologies. In this paper we focus on the first sub-problem and present an automatic procedure for extracting from a relational database schema its conceptual view. The semantic mapping between the database and its conceptualization is captured by associating views over the data source to elements of the extracted ontology. To represent the extracted conceptual model we use an ontology language, rather that a graphical notation, in order to provide precise formal semantics. Our approach uses heuristics based on ideas of standard relational schema design and normalization. Under this we formally prove that our technique preserves the semantics of constraints in the database. Therefore, there is no data loss, and the extracted model constitutes a faithful wrapper of the relational database.

@inproceedings{LuTe:DL07,
  author    = {Lina Lubyte and Sergio Tessaris},
  title     = {Extracting Ontologies from Relational Databases},
  booktitle = {Proceedings of the 20th International Workshop on
               Description Logics (DL 2007)},
  editor    = {Diego Calvanese and Enrico Franconi and Volker
	       Haarslev and Domenico Lembo and Boris Motik and
	       Sergio Tessaris and Anni-Yasmin Turhan},
  year      = {2007},
  pages     = {387-395},
  ISBN      = {978-88-6046-008-5}
}

The use of a conceptual model (or an ontology) to describe relational data sources has been proved to be extremely useful to overcome many important data access problems. However, the task of wrapping relational data sources by means of an ontology is mainly done manually. In this paper we introduce an automatic procedure for extracting a conceptual view from a relational database. The semantic mapping between the database schema and its conceptualisation is captured by associating views over the data source to elements of the extracted conceptual model. To represent the conceptual model we use an ontology language, rather that a graphical notation, in order to provide a precise formal semantics. In particular we adopt a variant of the DLR-Lite description logic because of its nice computational properties, and ability to express the mostly used modelling constraints. In order to uncover the connections between relational schema and the conceptual model, the heuristics underlying the ontology extraction process are based on ideas of standard relational schema design and normalisation. In fact, we assume that the relational source is in third normal form. Under this assumption we can formally prove that the conversion preserves the semantics of the constraints in the relational database. Therefore, there is no data loss, and the extracted model constitutes a faithful wrapper of the relational database.