Short paper: From streaming data to linked data. A case study with bike sharing systems

Current methods and tools that support Linked Data publication have mainly focused so far on static data, without considering the growing amount of streaming data available on the Web. In this paper we describe a case study that involves the publication of static and streaming Linked Data for bike sharing systems and related entities. We describe some of the challenges that we have faced, the solutions that we have explored, the lessons that we have learned, and the opportunities that lie in the future for exploiting Linked Stream Data

Enhancing Virtual Ontology Based Access over Tabular Data with Morph-CSV

Ontology-Based Data Access (OBDA) has traditionally focused on providing a unified view of heterogeneous datasets, either by materializing integrated data into RDF or by performing on-the fly querying via SPARQL query translation. In the specific case of tabular datasets represented as several CSV or Excel files, query translation approaches have been applied by considering each source as a single table that can be loaded into a relational database management system (RDBMS). Nevertheless, constraints over these tables are not represented; thus, neither consistency among attributes nor indexes over tables are enforced. As a consequence, efficiency of the SPARQL-to-SQL translation process may be affected, as well as the completeness of the answers produced during the evaluation of the generated SQL query. Our work is focused on applying implicit constraints on the OBDA query translation process over tabular data. We propose Morph-CSV, a framework for querying tabular data that exploits information from typical OBDA inputs (e.g., mappings, queries) to enforce constraints that can be used together with any SPARQL-to-SQL OBDA engine. Morph-CSV relies on both a constraint component and a set of constraint operators. For a given set of constraints, the operators are applied to each type of constraint with the aim of enhancing query completeness and performance. We evaluate Morph-CSV in several domains: e-commerce with the BSBM benchmark; transportation with a benchmark using the GTFS dataset from the Madrid subway; and biology with a use case extracted from the Bio2RDF project. We compare and report the performance of two SPARQL-to-SQL OBDA engines, without and with the incorporation of MorphCSV. The observed results suggest that Morph-CSV is able to speed up the total query execution time by up to two orders of magnitude, while it is able to produce all the query answers

Websogo: A global ontology for describing web sources

Based on the limitations raised by existing approaches in the context of the Semantic Web, we propose a formalism, Web Sources Global Ontology (WebSOGO), a data meta-model for the description of Web sources in terms of content, query-processing capabilities, service and navigation information. WebSOGO is formalized in the Object-Oriented paradigm using the Unified Modeling Language (UML). We also describe WebSOGO-S, a multi-layered system that will allow agents to discover, execute and compose Web sources through queries against a WebSOGO catalog of source ontologies. The UML specification of WebSOGO has been mapped to the Object-Relational (OR) model in Oracle; we define an Oracle cartridge with a list of types and methods that allow the specification of SQL queries against the WebSOGO catalog. By using the JDBC and ODBC drivers provided by Oracle, any agent or application will be able to contact WebSOGO-S

AVANTE: An architecture of CORBA components and XML Metadata for Web Based Instruction

Most current solutions for Web Based Instruction (WBI) use a centralized management model and a proprietary internal representation. The AVANTE Architecture is a WBI environment assembled using CORBA distributed components, implementing core services such as course management, user authentication, collaborative work, database access, presentation, and others. The AVANTE components conform to a 4-tiered model, with Client, Presentation, Management, and Low-Level Services component sublayers. Emergent XML standards for WBI describe all metadata definitions. Components at the Management layer manipulate JDBC-SQL data from the Low- Level Services Layer, and combine it with corresponding XML Schemas, instantiating course objects as new XML descriptions and component services. A filter-mapping service in the Presentation layer produces the dynamic HTML web pages needed for user interaction, processing these XML descriptions by applying one or more previously defined XSL stylesheets. A similar mechanism implements interface customization and remote service administration. The developed WBI system was deployed with open source software. Adding CORBA components easily achieves on-demand scalability. Future services include auditing, adaptive interfaces, grading, content development, and integration with existing systems

OnEQL: An Ontology Efficient Query Language Engine for the Semantic Web

Abstract. In this paper we describe the OnEQL system, a query engine that implements optimization techniques and evaluation strategies to speed up the evaluation time of querying and reasoning services in the Semantic Web. To identify execution plans that reduce the cost of evaluating a query, we developed a twofold optimization strategy that combines cost-based optimization and Magic Sets techniques. In the first stage, a dynamic programming-based algorithm is used to identify an ordering of predicates in the query that minimizes its estimated evaluation cost. In the second stage, Magic Sets techniques are used to push down query selections into the OnEQL ontology representation, in order to reduce the number of facts inferred during query evaluation. Additionally, we developed three physical operators that execute the sideways passing of bindings during the evaluation of the execution plan. To illustrate the advantages of this approach, we report the results of an experimental study over the most popular health ontologies.