Search by property
This page provides a simple browsing interface for finding entities described by a property and a named value. Other available search interfaces include the page property search, and the ask query builder.
List of results
- Adaptive Integration of Distributed Semantic Web Data + (An adaptive framework has been presented f … An adaptive framework has been presented for executing queries over multiple SPARQL endpoints that differs from existing approaches which use static query optimisation techniques. Many SPARQL web services are currently available and the number of them is growing. The work presented in this paper is a framework for executing queries over federations of such services. The framework proposed in this paper, which allows adaptive query processing over dynamically constructed predicate tables to be performed in conjunction with the construction of the predicate tables, was shown to perform relatively well in unpredictable environments where source query failures may occur. The prototype implemented was evaluated using real data, showing some advantage in terms of response times of adaptive over non-adaptive methods using a subset of DBPedia..aptive methods using a subset of DBPedia..)
- D2RQ – Treating Non-RDF Databases as Virtual RDF Graphs + (D2RQ offers a flexible, easy-to-use access mechanism to non-RDF databases. It allows the integration of legacy databases into the data access architecture currently standardized by the W3C Data Access Working Group)
- Querying Distributed RDF Data Sources with SPARQL + (DARQ offers a single interface for queryin … DARQ offers a single interface for querying multiple, distributed SPARQL end-points and makes query federation transparent to the client. One key feature of DARQ is that it solely relies on the SPARQL standard and therefore is compatible to any SPARQL endpoint implementing this standard. Using service descriptions provides a powerful way to dynamically add and remove endpoints to the query engine in a manner that is completely transparent to the user. To reduce execution costs we introduced basic query optimization for SPARQL queries. Our experiments show that the optimization algorithm can drastically improve query performance and allow distributed answering of SPARQL queries over distributed sources in reasonable time. Because the algorithm only relies on a very small amount of statistical information we expect that further improvements are possible using techniques. An important issue when dealing with data from multiple data sources are differences in the used vocabularies and the representation of information. In further work, we plan to work on mapping and translation rules between the vocabularies used by different SPARQL endpoints. Also, we will investigate generalizing the query patterns that can be handled and blank nodes and identity relationships across graphs.and identity relationships across graphs.)
- Querying over Federated SPARQL Endpoints : A State of the Art Survey + (Federation query over SPARQL Endpoints mad … Federation query over SPARQL Endpoints made a significant progress in the recent years. Although a number of federation frameworks have already been developed, the field is still relatively far from maturity. Based on our experience with the existing federation frameworks, the frameworks mostly focus on source selection and join optimization during query execution. In this work, we have presented a list of federation frameworks over SPARQL Endpoints along with their features. According to this list, the user can have considerations to choose the suitable federation framework for their case. We have classied those framework into three categories: i) framework interprets SPARQL 1.1 query to execute federation SPARQL query covering VALUES and SERVICE operator; ii) framework handles SPARQL 1.0 query and has responsibility to find relevant source for a query and join incoming result from SPARQL Endpoints; and iii) framework accepts SPARQL 1.0 and translate the incoming query to SPARQL 1.1 format. Based on the current generation of federation frameworks surveyed in this paper, it still requires further improvements to make frameworks more effective in a broader range of applications. We suggested several features that could be included in the future developments. Finally, we point out challenges for future research directions.challenges for future research directions.)
- Analysing Scholarly Communication Metadata of Computer Science Events + (In summary, we made the following observat … In summary, we made the following observations: With the number of submissions to the top conferences having tripled on average in the last three decades, acceptance rates are going down slightly. Most of those conferences that are A- or A*-rated today have a long continuity. In summary, we made the following observations: With the number of submissions to the top conferences having tripled on average in the last three decades, acceptance rates are going down slightly. Most of those conferences that are A- or A*-rated today have a long continuity. Geographical distribution is not generally relevant; some good conferences take place in the same location; others cycle between continents. Good conferences always take place around the same time of the year. This might mean that the community got used to them being important events. Some topics have attracted increasing interest recently e.g., database topics thanks to the `big data' trend. This might be confirmed by further investigations into more recent, emerging events in such fields.re recent, emerging events in such fields.)
- Towards a Knowledge Graph Representing Research Findings by Semantifying Survey Articles + (In this article, we presented SemSur, a Se … In this article, we presented SemSur, a Semantic Survey Ontology, and an approach for creating a comprehensive knowledge graph representing research findings. We see this work as an initial step of a long-term research agenda to create a paradigm shift from document-based to knowledge-based scholarly communication. Our vision is to have this work deployed in an extended version of the existing OpenResearch.org platform. We have created instances of three selected surveys on different fields of research using the SemSur ontology. We evaluated our approach involving nine researchers. As we see in the evaluation results, SemSur enables successful retrieval of relevant and accurate results without users having to spend much time and effort compared to traditional ways. This ontology can have a significant influence on the scientific community especially for researchers who want to create a survey article or write literature on a certain topic. The results of our evaluation show that researchers agree that the traditional way of gathering an overview on a particular research topic is cumbersome and time-consuming. Much effort is needed and important information might be easily overlooked. Collaborative integration of research metadata provided by the community supports researchers in this regard. Interviewed domain experts mentioned that it might be necessary to read and understand 30 to 100 scientific articles to get a proper level of understanding or an overview of a topic or sub-topics. A collaboration of researchers as owners of each particular research work to provide a structured and semantic representation of their research achievements can have a huge impact in making their research more accessible. A similar effort is spent on preparing survey and overview articles.on preparing survey and overview articles.)
- A Semantic Web Middleware for Virtual Data Integration on the Web + (In this contribution a mediator-based syst … In this contribution a mediator-based system for virtual data integration based on SemanticWeb technology has been presented. The system is primarily developed for sharing scientific data, but because of its generic architecture, it is supposed to be used for many other Semantic Web applications. In this paper query federation based on SPARQL and Jena/ARQ has been demonstrated in detail and several concepts for query optimization which is currently on the agenda have been discussed. Additional contributions can be expected after the implementation of additional features mentioned before.n of additional features mentioned before.)
- From Relational Data to RDFS Models + (In this paper we have introduced FDR2 – a … In this paper we have introduced FDR2 – a technique that enables us to link relational and RDF/S data models. According to FDR2 a relational schema is automatically created to explicate the structure and internal relationships between elements of a relational collection of data. Explication of virtual relations allows the user to construct a relational schema specific RDMap by defining relationships between concepts from the relational schema and a domain ontology. The actual relational data are automatically expressed in RDF according to the generated relational schema. Run-time integration is achieved by applying an RDFS reasoner to merge the above-mentioned components into a single RDFS model and to deduct necessary entailments. A resulting run-time model allows to access the relational data with queries termed according to the domain ontology. FDR2 is purely RDF/S-based and does not require any additional software components except an RDFS reasoner.ftware components except an RDFS reasoner.)
- Relational.OWL - A Data and Schema Representation Format Based on OWL + (In this paper we have shown how to represe … In this paper we have shown how to represent schema and data items originally stored in relational database systems using our own OWL ontology. Relational.OWL enables us to semantically represent the schema of any relational database. This representation itself can be interpreted, due to the properties of OWL Full, as a novel ontology. Based on the latter ontology, we can now semantically represent the data stored in this specific database. The advantage of this representation technique is obvious: Both, schema and data changes can automatically be transferred to and processed by any remote database system, which is able to understand knowledge representation techniques used within OWL. Misunderstandings are impossible.Besides the refinement and completion of the concrete schema representation, we consider on how to adopt our technique to other types of database systems. Similar solutions can easily be found for Object-Oriented Databases, Hierarchical Databases like IMS, or its hybrid the modern and more common X.500 or LDAP Directory Systemsore common X.500 or LDAP Directory Systems)
- Querying the Web of Data with Graph Theory-based Techniques + (In this paper we present a novel graph the … In this paper we present a novel graph theory-based approach for improved performance and scalability of distributed SPARQL query processing. We propose several key techniques adopted in the distributed SPARQL query engine that we developed (GDS). First, an extended MST algorithm which supports arbitrary SPARQL queries and provides better performance. Second, a simplified cost model using run-time statistics that lows requirement of service descriptions but provides good cost estimations. Third, a combination of semi-join and bind-join along with local cache that reduce network tracffic. We also compare our approach with DARQ and FedX in terms of performance and scalability. The results suggest that graph theory-based approach using lightweight service descriptions can provide better performance and scalability over other approaches Although these results are encouraging, the potential of graph theory-based approach can be developed further. First, GDS applies MST-based algorithm to BGPs rather than the whole query. BGPs are optimized separately even they are from the same query (i.e. UNION and OPTIONAL queries). In the future we aim to work on representing the whole query as a single graph and therefore provide better optimization for queries having multiple BGPs. Second, GDS does not take advantage of FILTER in optimization, which would further improve performance. Third, accurate and detailed service descriptions matters. The more accurate statistics we have, the more optimal query plan we get. Currently collecting quality service descriptions are not feasible on a large scale since most SPARQL endpoints do not provide service descriptions. However, this situation is improving as more and more approaches coming up. For example, SPARQL 1.1 aggregation features enable us to collect service descriptions more efficiently, and VoiD encourages SPARQL endpoints to publish service descriptions as well. Fourth, aggregation features in the upcoming SPARQL 1.1 (e.g. BINDINGS) can also save much efforts of our approach. In addition to these improvements, we are planning to explore the co-reference issue in the Linked Data cloud. From the perspective of distributed SPARQL queries, this issue is getting worse as more data are published , and we plan to address this issue by using our Virtual Graph approach.issue by using our Virtual Graph approach.)
- Avalanche: Putting the Spirit of the Web back into Semantic Web Querying + (In this paper we presented Avalanche , a n … In this paper we presented Avalanche , a novel approach for querying the Web of Data that (1) makes no assumptions about data distribution, availability, or partitioning, (2) provides up-to-date results, and (3) is flexible since it assumes nothing about the structure of participating triple stores. Specifically, we showed that Avalanche is able to execute non-trivial queries over distributed data-sources with an ex-ante unknown data-distribution. We showed two possible utility functions to guide the planning and execution over the distributed data-sources—the basic simple model and an extended model exploiting join estimation. We found that whilst the simple model found some results faster it did find less results than the extended model using the same stopping criteria. We believe that if we were to query huge information spaces the overhead of badly selected plans will be subdued by the better but slower plans of the extended utility function. To our knowledge, Avalanche is the first Semantic Web query system that makes no assumptions about the data distribution whatsoever. Whilst it is only a first implementation with a number of drawbacks it represents a first important towards bringing the spirit of the web back to triple-stores—a major condition to fulfill the vision of a truly global and open Semantic Web.n of a truly global and open Semantic Web.)
- RDB2ONT: A Tool for Generating OWL Ontologies From Relational Database Systems + (In this paper, an algorithm and tool for g … In this paper, an algorithm and tool for generating OWL ontologies from relational database systems is presented. The tool, RDB2ONT, helps the domain experts to quickly generate and publish OWL ontologies describing the underlying relational database systems while preserving their structural constraints. The generated ontologies are constructed using a set of vocabularies and structures defined in schema that describes relational database systems on the web so they guarantees that user applications can work with data instances that conformed to a set of known vocabularies and structures. The generated ontologies provide a standardized and meaningful way for describing the underlying relational database systems so they “bridge” the semantic gaps between the ontologies describing relational database systems and/or the ontologies describing other data sources on the web such as flat-files, semi-structures, etc. Concepts in OWL ontologies can be defined at multiple levels of granularities thus the generated OWL ontologies can be used to address the semantic heterogeneity problem at multiple levels. Evolutions of database systems in large-scale environments are inevitable so by using the RDB2ONT tool, OWL ontologies can be re-generated with little effort from the domain experts thus speed up the process of facilitating data in the underlying relational database systems with other data sources on the web. Although the generated OWL ontologies provide the explicit meaning of concepts and their semantic relationships between related concepts, there are still many open research questions that need to be addressed. One of the questions is how to merge the generated OWL ontologies into an integrated OWL ontology so that common views of concepts can be achieved? This would allow users to pose queries on the common views of concepts rather than the concepts defined in the individual ontologies.epts defined in the individual ontologies.)
- Unveiling the hidden bride: deep annotation for mapping and migrating legacy data to the Semantic Web + (In this paper, we have described deep anno … In this paper, we have described deep annotation, an original framework to provide semantic annotation for large sets of data. Deep annotation leaves semantic data where it can be handled best, viz. in database systems. Thus, deep annotation provides a means for mapping and reusing dynamic data in the Semantic Web with tools that are comparatively simple and intuitive to use. To attain this objective we have defined a deep annotation process and the appropriate architecture. We have incorporated the means for server-side markup that allows the user to define semantic mappings by using OntoMat-Annotizer to create Web presentation-based annotations 12 and OntoMat-Reverse to create schema-based annotations. An ontology and mapping editor and an inference engine are then used to investigate and exploit the resulting descriptions either for querying the database content or to materialize the content into RDF files. In total, we have provided a complete framework and its prototype implementation for deep annotation.totype implementation for deep annotation.)
- Querying the Web of Interlinked Datasets using VOID Descriptions + (In this paper, we have introduced a query … In this paper, we have introduced a query federation engine called WoDQA that discovers related datasets in a VOID store for a query and distributes the query over these datasets. The novelty of our approach is exhaustive dataset selection mechanism which includes analysis of triple pattern relations and links between datasets besides analyzing datasets for each triple pattern. WoDQA focuses on discovering relevant datasets and eliminating irrelevant ones using a rule-based approach introduced in this paper. Our approach requires query the dataset, reflect actual content of the dataset completely and accurately, and include linksets between datasets to select datasets ectively. WoDQA allows users to construct raw queries without the need to know how query will divide into sub-queries and where sub-queries are executed. Query results are complete under the assumption of available, accurate and complete VOID descriptions of datasets. The initial version of WoDQA which is introduced in this paper has some disadvantages arising from query federation approach which WoDQA builds upon. As mentioned previously, follow-your-nose has some problems such as missing results and large document retrieval. Similar problems may occur for query federation. Firstly, to find complete results to queries, it is required that metadata of all datasets must be well-defined and accurate. But, to provide such an accurate dataset metadata an automated mechanism which continuously updates the metadata is required. However, even there would be a tool which implements this requirement, providing accurate dataset metadata via such a tool is the responsibility of dataset publishers. Another problems of query federation are high latency and low selectivity of datasets which are similar to retrieval of large documents in follow-your-nose. Query optimization can be a solution for these problems of query federation. Grouping triple patterns to lter more triples on an endpoint can prevent high latency (required processing time) and changing query evaluation order according to dataset selectivity statistics can prevent retrieving large result sets. To make WoDQA functioning in the wild, optimization step of query federation is required to be implemented. We plan to incorporate triple pattern selectivity into query reorganization using VOID properties about statistics. On the other hand, we could not make an evaluation of our approach in this paper, since VOID documents in current VOID stores are not well-dened. Since SPARQL endpoint denitions, linkset descriptions or vocabularies are missing in most of VOID documents, we could not nd a chance to execute comprehensive scenarios. Developing a tool which extracts well-dened VOID descriptions of datasets, and by this means evaluating our approach is a required future work to confirm applicability of WoDQA on linked open data. Also, evaluating the analysis cost of WoDQA for a large VOID store will be possible when well-dened VOIDs are constructed.ble when well-dened VOIDs are constructed.)
- LogMap: Logic-based and Scalable Ontology Matching + (In this paper, we have presented LogMap, a … In this paper, we have presented LogMap, a highly scalable ontology matching tool with built-in reasoning and diagnosis capabilities. LogMap's features and scalability behaviour make it well-suited for matching large-scale ontologies. LogMap, however, is still an early-stage prototype and there is plenty of room for improvement.d there is plenty of room for improvement.)
- DataMaster – a Plug-in for Importing Schemas and Data from Relational Databases into Protégé + (In this paper, we have presented the DataM … In this paper, we have presented the DataMaster Protégé plug-in, which allows a user to import schema structures and data from relational databases accessible through JDBC. We have presented the four ontologies that can be used to represent the database structure and the table data and finally we have given a short overview of the different import options available in the DataMaster plug-in.tions available in the DataMaster plug-in.)
- Cross: an OWL wrapper for teasoning on relational databases + (In this paper, we have proposed the ODBC m … In this paper, we have proposed the ODBC model, a formalization of relational databases focusing on their logic model. We have then presented a transformation of that model into OWL, a DL-based language designed for the Semantic Web. This transformation is implemented by the Cross open-source prototype, which effectively introduces the interesting notion of semantic values. We proved that the knowledge-based produced by this transformation is consistent if and only if the source database state is weakly legal (i.e. legal but regarding foreign key constraints). Taking advantage of that result, we have shown how that transformation can prove useful for the purpose of analysing legacy RDBs, enhancing existing RDBs with additional constraints, and integrating them in the SW.nstraints, and integrating them in the SW.)
- SLINT: A Schema-Independent Linked Data Interlinking System + (In this paper, we present SLINT, an effici … In this paper, we present SLINT, an efficient schema-independent linked data interlinking system. We select important predicates by predicate’s coverage and discriminability. The predicate alignments are constructed and filtered for obtaining key alignments.We implement an adaptive filtering technique to produce candidates and identities. Compare with the most recent systems, SLINT highly outperforms the precision and recall in interlinking. The performance of SLINT is also very high when it takes around 1 minute to detect more than 13,000 identity pairs.to detect more than 13,000 identity pairs.)
- Accessing and Documenting Relational Databases through OWL Ontologies + (In this paper, we presented a completely a … In this paper, we presented a completely automated approach to map relational databases and ontologies. The system proposed is capable of extracting an ontological view of the relational schema, and to enable SPARQL access to the relational data source by means of a query rewriting mechanism. The same approach can be used to efficiently store relational ontologies on a RDBMS; moreover, the mapping we devised is completely based on OWL with no need to resort to a new formalism. The impact of this system has been discussed considering three main applications: (i) publishing of relational data in an ontological format, (ii) documentation of relational schemas by means of ontological annotations, and (iii) efficient relational storage for data-intensive ontologies.nal storage for data-intensive ontologies.)
