Nektarios Gioldasis

Ontology mapping and SPARQL rewriting for querying federated RDF data sources

The web of data consists of distributed, diverse (in terms of schema adopted), and large RDF datasets. In this paper we present a SPARQL query rewriting method which can be used to achieve interoperability in semantic information retrieval and/or knowledge discovery processes over interconnected RDF data sources. Formal mappings between different overlapping ontologies are exploited in order to rewrite initial user SPARQL queries, so that they can be evaluated over different RDF data sources on different sites. The proposed environment is utilized by an ontology-based mediator system, which we have developed in order to provide data integration within the Semantic Web environment.

SPARQL-RW: transparent query access over mapped RDF data sources

The Web of Data is an open environment consisting of very large, inter-linked RDF datasets from various domains (e.g., DBpedia, GeoNames, ACM, PubMed, etc.) accessed through SPARQL queries. Establishing interoperability in this environment has become a major research challenge. This paper presents Sparql--Rw (SPARQL--ReWriting), a framework which provides transparent query access over mapped RDF datasets. The Sparql--Rw provides a generic method for SPARQL query rewriting, with respect to a set of predefined mappings between ontology schemas. To this end, it supports a set of rich and flexible mapping types and it is proved to provide semantics preserving queries.

Querying XML Data with SPARQL

SPARQL is today the standard access language for Semantic Web data. In the recent years XML databases have also acquired industrial importance due to the widespread applicability of XML in the Web. In this paper we present a framework that bridges the heterogeneity gap and creates an interoperable environment where SPARQL queries are used to access XML databases. Our approach assumes that fairly generic mappings between ontology constructs and XML Schema constructs have been automatically derived or manually specified. The mappings are used to automatically translate SPARQL queries to semantically equivalent XQuery queries which are used to access the XML databases. We present the algorithms and the implementation of SPARQL2XQuery framework, which is used for answering SPARQL queries over XML databases.

Towards a Mediator Based on OWL and SPARQL

We propose a framework that supports a federated environment based on a Mediator Architecture in the Semantic Web. The Mediator supports mappings between the OWL Ontology of the Mediator and the other ontologies in the federated sites. SPARQL queries submitted to the Mediator are decomposed and reformulated to SPARQL queries to the federated sites. The evaluated results return to the Mediator. In this paper we describe the mappings definition and encoding. We also discuss briefly the reformulation approach that is used by the Mediator system that we are currently implementing.

The SPARQL2XQuery interoperability framework

In the context of the emergent Web of Data, a large number of organizations, institutes and companies (e.g., DBpedia, Data.gov, GeoNames, PubMed) adopt the Linked Data practices. Utilizing the Semantic Web (SW) technologies, they publish their data and offer SPARQL endpoints (i.e., SPARQL-based search services). On the other hand, the dominant standard for information exchange in the Web today is XML. Additionally, many international standards (e.g., Dublin Core, MPEG-7, METS, TEI, IEEE LOM) in several domains (e.g., Digital Libraries, GIS, Multimedia, e-Learning) have been expressed in XML Schema. The aforementioned have led to an increasing emphasis on XML data, accessed using the XQuery query language. The SW and XML worlds and their developed infrastructures are based on different data models, semantics and query languages. Thus, it is crucial to develop interoperability mechanisms that allow the Web of Data users to access XML datasets, using SPARQL, from their own working environments. It is unrealistic to expect that all the existing legacy data (e.g., Relational, XML, etc.) will be transformed into SW data. Therefore, publishing legacy data as Linked Data and providing SPARQL endpoints over them has become a major research challenge. In this direction, we introduce the SPARQL2XQuery Framework which creates an interoperable environment, where SPARQL queries are automatically translated to XQuery queries, in order to access XML data across the Web. The SPARQL2XQuery Framework provides a mapping model for the expression of OWL–RDF/S to XML Schema mappings as well as a method for SPARQL to XQuery translation. To this end, our Framework supports both manual and automatic mapping specification between ontologies and XML Schemas. In the automatic mapping specification scenario, the SPARQL2XQuery exploits the XS2OWL component which transforms XML Schemas into OWL ontologies. Finally, extensive experiments have been conducted in order to evaluate the schema transformation, mapping generation, query translation and query evaluation efficiency, using both real and synthetic datasets.

The XML and Semantic Web Worlds: Technologies, Interoperability and Integration: A Survey of the State of the Art

In the context of the emergent Web of Data, a large number of organizations, institutes and companies (e.g., DBpedia,ACM, IEEE, IBM, NASA,BBC,etc.) adopt the Linked Data practices and publish their data utilizing Semantic Web (SW) technologies. On the other hand, the dominant standard for information exchange in the Web today is XML. Many international standards (e.g., Dublin Core, MPEG-7,METS, TEI, IEEE LOM,etc.) have been expressed in XML Schema resulting to a large number of XML datasets. The SW and XML worlds and their developed infrastructures are based on different data models, semantics and query languages. Thus, it is crucial to provide interoperability and integration mechanisms to bridge the gap between the SW and XML worlds.

A Service Oriented Architecture for Managing Operational Strategies

In this paper we present a case study where an e-business platform (OPERATIONS) has to be built in order to manage the operational strategies of a high volume coastal company. The platform is intended to support multiple operational scenarios that have to be executed when emergency situations or sudden changes of scheduled events unfold. In order to properly integrate all the involved parties that may take part in such a scenario, the system must support multiple interaction patterns according to the communication channel and the device that is used. Thus, its design must take into account multi-channel delivery of functionality and information. The design of the system follows a Service Oriented Architecture (SOA) in order to properly integrate back-office data sources and legacy systems with new required application extensions providing a complete e-business platform. The core business logic tier of the system is a Process Oriented Platform (POP) that is able to dynamically generate the appropriate workflows, to orchestrate the constituent services and to execute complex operational scenarios interacting with involved users and systems in a multi-channel fashion. Finally, appropriate knowledge bases have been defined to support the storage, evaluation, and evolution of the executed scenarios and to provide valuable Business Activity Monitoring information to the company’s administration.

SPARQL2XQuery 2.0: Supporting Semantic-based queries over XML data

The dominant standards in multimedia content and service description, namely the MPEG-7 and the MPEG-21, have been expressed in XML Schema syntax. In addition, ontologies that capture the semantics of these standards have been developed using the semantic web languages. Since different communities in the industry and the academia work and are familiar with the Semantic Web environment or the XML environment, a Schema mapping framework and a Query mapping framework are needed that will allow querying multimedia content and service descriptions in a uniform way in both the XML and Semantic Web environments. We present in this paper SPARQL2XQuery 2.0, a framework that allows expressing semantic queries on top of XML data through the translation of SPARQL queries in XQuery syntax. SPARQL2XQuery 2.0 may work with both existing ontologies and with automatically produced ones, formed according to our XS2OWL 2.0 transformation model. XS2-OWL 2.0 exploits the OWL 2.0 semantics and supports the new XML constructs introduced by XML Schema 1.1.

Rich metadata and context capturing through CIDOC/CRM and MPEG-7 interoperability

It is now accepted that powerful retrieval of multimedia data can be achieved with the integration of semantic and contextual metadata that relate to multimedia objects. In the case of objects related to culture and history there is a wealth of related information stored in Digital Libraries. CIDOC/CRM is a new, rapidly adopted standard in the field of cultural heritage that provides a very powerful model for encoding cultural heritage knowledge. In this paper we propose that knowledge is extracted and encoded in MPEG-7 multimedia object descriptions in an automatic manner so that the multimedia objects are augmented with very rich metadata descriptions coming from Digital Libraries. We analyze the mapping problem between CIDOC/CRM and MPEG-7 and we present the algorithms and a software system that supports this mapping.

A Knowledge Management Platform for Supporting Digital Business Ecosystems based on P2P and SOA technologies

We consider a digital business ecosystem environment where SMEs cooperate and compete. We aim to provide to each SME and the ecosystem with knowledge management mechanisms to support their needs for information, service findings and recommendations. We present the design and implementation of a platform that supports the knowledge management needs in this environment. We describe the business related knowledge managed by the knowledge base (KB), as well as the architectural components and the core services supported by the KB infrastructure. Since the SMEs are independent and their KB contents are evolving we adopted a P2P framework for the cooperation of SMEs. We present the P2P framework and we outline the knowledge discovery and replication mechanisms supported by the implementation. The knowledge management mechanisms described in this paper form the infrastructure for knowledge management of the Digital Business Ecosystem IP project of EU.