Papers by Dimitrios-Emmanuel Spanos
Materializing the Web of Linked Data
This book explains the Linked Data domain by adopting a bottom-up approach: it introduces the fun... more This book explains the Linked Data domain by adopting a bottom-up approach: it introduces the fundamental Semantic Web technologies and building blocks, which are then combined into methodologies and end-to-end examples for publishing datasets as Linked Data, and use cases that harness scholarly information and sensor data. It presents how Linked Data is used for web-scale data integration, information management and search. Special emphasis is given to the publication of Linked Data from relational databases as well as from real-time sensor data streams. The authors also trace the transformation from the document-based World Wide Web into a Web of Data. Materializing the Web of Linked Data is addressed to researchers and professionals studying software technologies, tools and approaches that drive the Linked Data ecosystem, and the Web in general.
7th Metadata and Semantics Research Conference (MTSR'13)
As far as digital repositories are concerned, numerous benefits
emerge from the disposal of thei... more As far as digital repositories are concerned, numerous benefits
emerge from the disposal of their contents as Linked Open Data (LOD). This leads more and more repositories towards this direction. However, several factors need to be taken into account in doing so, among which is whether the transition needs to be materialized in real-time or in asynchronous time intervals. In this paper we provide the problem framework in the context of
digital repositories, we discuss the benefits and drawbacks of both approaches and draw our conclusions after evaluating a set of performance measurements. Overall, we argue that in contexts with infrequent data updates, as is the case with digital repositories, persistent RDF views are more efficient than real-time
SPARQL-to-SQL rewriting systems in terms of query response times, especially when expensive SQL queries are involved.
International Journal of Ad Hoc and Ubiquitous Computing, 2012
As data proliferates at increasing rates, the need for real-time stream processing applications i... more As data proliferates at increasing rates, the need for real-time stream processing applications increases as well. In the same way that Data Stream Management Systems (DSMS) have emerged from the database community, there is now a similar concern in managing dynamic knowledge among the Semantic Web community. Unfortunately, early relevant approaches are, to a large extent, theoretical and do not present convincing evidence of their efficiency in real dynamic environments. In this paper, we present a framework for the effective, real-time processing of streaming data and we define and analyse in depth its key components. Our framework serves as a basis for the implementation of the SensorStream prototype, on which we run numerous performance and scalability measurements that outline its behaviour and demonstrate its suitability and scalability for solutions that require real-time information processing from distributed and heterogeneous data sources.
Semantic Web, 2012
Relational databases are considered one of the most popular storage solutions for various kinds o... more Relational databases are considered one of the most popular storage solutions for various kinds of data and they have been recognized as a key factor in generating huge amounts of data for Semantic Web applications. Ontologies, on the other hand, are one of the key concepts and main vehicle of knowledge in the Semantic Web research area. The problem of bridging the gap between relational databases and ontologies has attracted the interest of the Semantic Web community, even from the early years of its existence and is commonly referred to as the database-to-ontology mapping problem. However, this term has been used interchangeably for referring to two distinct problems: namely, the creation of an ontology from an existing database instance and the discovery of mappings between an existing database instance and an existing ontology. In this paper, we clearly define these two problems and present the motivation, benefits, challenges and solutions for each one of them. We attempt to gather the most notable approaches proposed so far in the literature, present them concisely in tabular format and group them under a classification scheme. We finally explore the perspectives and future research steps for a seamless and meaningful integration of databases into the Semantic Web.
17th International Workshop on Energy-Aware Communications, 2011
Decision making in decentralized and dynamic environments is challenging due to the continuous ch... more Decision making in decentralized and dynamic environments is challenging due to the continuous changes in the network topology and the absence of specific nodes that are responsible to take decisions. These challenges are increased in case of sensor networks deployments. In this paper, a novel approach is presented for realizing distributed data fusion and reasoning in wireless sensor networks. The approach is based on the storage and retrieval of data in stable overlay networks that abstract the physical network topology and the design of proper mechanisms for the semantic annotation of the available information in order to be used in the decision making process.
Data Management in the Semantic Web, 2011
The increasing availability of small-size sensor devices during the last few years and the large ... more The increasing availability of small-size sensor devices during the last few years and the large amount of data that they generate has led to the necessity for more efficient methods regarding data management. In this chapter, we review the techniques that are being used for data gathering and information management in sensor networks and the advantages that are provided through the proliferation of Semantic Web technologies. We present the current trends in the field of data management in sensor networks and propose a three-layer flexible architecture which intends to help developers as well as end users to take advantage of the full potential that modern sensor networks can offer. This architecture deals with issues regarding data aggregation, data enrichment and finally, data management and querying using Semantic Web technologies. Semantics are used in order to extract meaningful information from the sensor's raw data and thus facilitate smart applications development over large-scale sensor networks. * Corresponding author: E-mail address: tzafeir@cn.ntua.gr, Phone: +302107722425 A. Zafeiropoulos, D.E. Spanos, S. Arkoulis et al. 98
Cognitive radio-aided wireless sensor networks for emergency response
Measurement …, 2010
Abstract A lot of research effort has been put into wireless sensor networks (WSNs) and several m... more Abstract A lot of research effort has been put into wireless sensor networks (WSNs) and several methods have been proposed to minimize the energy consumption and maximize the network's lifetime. However, little work has been carried out regarding WSNs deployed ...
International Journal of Web Engineering and Technology, 2010
After several years of research, the fundamental Semantic Web technologies have reached a high ma... more After several years of research, the fundamental Semantic Web technologies have reached a high maturity level. Nevertheless, the average Web user has not yet taken advantage of their full potential. In this paper, we introduce the Semantic Web bottleneck, analyse the main problems that preserve it and suggest ways to overcome it. In particular, we discuss the issues involved in deploying, maintaining and using semantically rich Web applications, decomposing this process into two primal ones: publishing and exploiting semantic content. We analyse the role of key players such as the Web industry, the search engines, the academia, the Web user, and the Web engineers that essentially materialise and use these technologies. A roadmap is provided in order for the Semantic Web to gain further acceptance, based on three major axes: simplicity, mainly entailed by automation, integration with the existing technologies and practices, and adoption by the Web industry driving forces.
The Second International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies, 2008. UBICOMM '08., 2008
In this paper, we present a three-layer flexible architecture which intends to help developers an... more In this paper, we present a three-layer flexible architecture which intends to help developers and end users to take advantage of the full potential that modern sensor networks can offer. The proposed architecture deals with issues regarding data aggregation, data enrichment and finally, data management and querying using semantic Web techniques. Semantics are used in order to extract meaningful information from the sensorpsilas raw data and thus facilitate smart applications development over large-scale sensor networks. We describe an open, standards-based, modular architecture which is based on the current standardization efforts of the open geospatial consortium (OGC) and extends them to support semantic Web techniques comprising a core of reusable components and interfaces for supporting different types of services, through Web technologies.
Journal of Web Engineering, 2008
In this paper we discuss the problem of mapping relational database contents and ontologies. The ... more In this paper we discuss the problem of mapping relational database contents and ontologies. The motivation lies in the fact that during the latest years, the evolution in Web Technologies rendered the addition of intelligence to the information residing on the Web a necessity. We argue that the addition of formal semantics to the databases that store the majority of information found in the Web is important, in order to make this information searchable, accessible and retrievable. The key technologies towards this direction are the Semantic Web and the ontologies. We analyze in this paper the approaches that have so far been presented in order to exploit the prospects that such collaboration promises. We set the theoretical and practical boundaries of the mapping problem, we delve into the tools that altogether comprise today's state of the art, and we provide a discussion about the benefits and the drawbacks of the existing approaches. We discuss the feasibility and viability of applying the mappings in real world applications as well as the directions that the evolution of current implementations should follow. We conclude by presenting the requirements that should be met in order to provide a more powerful next generation of mapping frameworks.
International CAiSE Workshop on Web Information Systems Modeling (WISM’06), 2006
This paper introduces an approach to mapping relational database contents to ontologies. The curr... more This paper introduces an approach to mapping relational database contents to ontologies. The current effort is motivated by the need of including into the Semantic Web volumes of web data not satisfied by current search engines. A graphical tool is developed in order to ease the mapping procedure and export enhanced ontologies linked to database entities. Moreover, queries using semantic web query languages can be imposed to the database through its connection to an ontology. Using Protégé, we were able to map ontology instances into relational databases and retrieve results by semantic web query languages.
Uploads
Papers by Dimitrios-Emmanuel Spanos
emerge from the disposal of their contents as Linked Open Data (LOD). This leads more and more repositories towards this direction. However, several factors need to be taken into account in doing so, among which is whether the transition needs to be materialized in real-time or in asynchronous time intervals. In this paper we provide the problem framework in the context of
digital repositories, we discuss the benefits and drawbacks of both approaches and draw our conclusions after evaluating a set of performance measurements. Overall, we argue that in contexts with infrequent data updates, as is the case with digital repositories, persistent RDF views are more efficient than real-time
SPARQL-to-SQL rewriting systems in terms of query response times, especially when expensive SQL queries are involved.