Boris Vrdoljak

Data warehouse design from XML sources

A large amount of data needed in decision-making processes is stored in the XML data format, which is widely used for e-commerce and Internet-based information exchange. Thus, as more organizations view the web as an integral part of their communication and business, the importance of integrating XML data in data warehousing environments is becoming increasingly high. In this paper we show how the design of a data mart can be carried out starting directly from an XML source. Two main issues arise: on the one hand, since XML models semi-structured data, not all the information needed for design can be safely derived; on the other, different approaches for representing relationships in XML DTDs and Schemas are possible, each with different expressive power. After discussing these issues, we propose a semi-automatic approach for building the conceptual schema for a data mart starting from the XML sources.

Designing Web Warehouses from XML Schemas

Web warehousing plays a key role in providing the managers with up-to-date and comprehensive information about their business domain. On the other hand, since XML is now a standard de facto for the exchange of semi-structured data, integrating XML data into web warehouses is a hot topic. In this paper we propose a semi-automated methodology for designing web warehouses from XML sources modeled by XML Schemas. In the proposed methodology, design is carried out by first creating a schema graph, then navigating its arcs in order to derive a correct multidimensional representation. Differently from previous approaches in the literature, particular relevance is given to the problem of detecting shared hierarchies and convergence of dependencies, and of modeling many-to-many relationships. The approach is implemented in a prototype that reads an XML Schema and produces in output the logical schema of the warehouse.

Automated Integration of Heterogeneous Data Warehouse Schemas

A federated data warehouse is a logical integration of data warehouses applicable when physical integration is impossible due to privacy policy or legal restrictions. In healthcare systems federated data warehouses are a most feasible source of data for deducing guidelines for evidence-based medicine based on data material from different participating institutions. In order to enable the translation of queries in a federated approach, schemas of the federated warehouse and the local warehouses must be matched. In this paper we present a procedure that enables the matching process for schema structures specific to the multidimensional model of data warehouses: facts, measures, dimensions, aggregation levels and dimensional attributes. Similarities between warehouse-specific structures are computed by using linguistic and structural comparison. The calculated values are used to create necessary mappings.

CroMatcher: An ontology matching system based on automated weighted aggregation and iterative final alignment

In order to perform ontology matching with high accuracy, while at the same time retaining applicability to most diverse input ontologies, the matching process generally incorporates multiple methods. Each of these methods is aimed at a particular ontology component, such as annotations, structure, properties or instances. Adequately combining these methods is one of the greatest challenges in designing an ontology matching system. In a parallel composition of basic matchers, the ability to dynamically set the weights of the basic matchers in the final output, thus making the weights optimal for the given input, is the key breakthrough for obtaining first-rate matching performance. In this paper we present CroMatcher, an ontology matching system, introducing several novelties to the automated weight calculation process. We apply substitute values for matchers that are inapplicable for the particular case and use thresholds to eliminate low-probability alignment candidates. We compare the alignments produced by the matchers and give less weight to the matchers producing mutually similar alignments, whereas more weight is given to those matchers whose alignment is distinct and rather unique. We also present a new, iterative method for producing one-to-one final alignment of ontology structures, which is a significant enhancement of similar non-iterative methods proposed in the literature. CroMatcher has been evaluated against other state-of-the-art matching systems at the OAEI evaluation contest. In a large number of test cases it achieved the highest score, which puts it among the state-of-the-art leaders.

Word Sense Disambiguation as the Primary Step of Ontology Integration

The recommendable primary step of ontology integration is annotation of ontology components with entries from WordNet or other dictionary sources in order to disambiguate their meaning. This paper presents an approach to automatically disambiguating the meaning of OWL ontology classes by providing sense annotation from WordNet. A class name is disambiguated using the names of the related classes, by comparing the taxonomy of the ontology with the portions of the WordNet taxonomy corresponding to all possible meanings of the class. The equivalence of the taxonomies is expressed by a probability function called affinity function. We apply two different basic techniques to compute the affinity coefficients: one based on semantic similarity calculation and the other on analyzing overlaps between word definitions and hyponyms. A software prototype is provided to evaluate the approach, as well as to determine which of the two disambiguation techniques produces better results.

Integrating XML sources into a data warehouse

Since XML has become a standard for data exchange over the Internet, especially in B2B and B2C communication, there is an increasing need of integrating XML data into data warehousing systems. In this paper we propose a methodology for data warehouse design, when data sources are XML Schemas and conforming XML documents. Particular relevance is given to the conceptual and logical multidimensional design. A prototype tool has been developed to verify and support our methodology. Because of the semi-structured nature of XML data, not all the information needed for design can be safely derived from XML Schema. In these situations, XQuery statements are generated by the tool to examine XML documents. The functionality of the tool is explained on a real-life XML Schema that describes purchase orders.

Towards Dynamic Web Service Generation on Demand

The Web services technology enables communication, distributed computation and interoperability in heterogeneous environments. Although the technology is well specified and supported by the programming tools, it is still not widely used. Some of the main reasons are the difficulties which the end users have in searching an adequate Web service to get the required data. Even if found, the Web service rarely fit the exact needs. This paper presents a new framework for dynamical generation of the Web services from the heterogeneous data sources on users demand. The aim of the framework is to generate web services that are customized to the particular requirements. Apart from specifying the requirements in WSDL, the framework proposes the ontology for describing the available data

Automated weighted aggregation in an ontology matching system

Ontology matching is the process of finding semantic relationships between entities of different ontologies. It plays an important role in the integration of heterogeneous data sources. To find semantic correspondences between entities, various matchers can be used. When multiple matchers are integrated into a matching system, the issue of combining these matchers together and determining the importance of every basic matcher arises. In a parallel composition of basic matchers, several matchers are used independently and then their results are aggregated. In this paper, we propose a method for automatically determining weights of basic matchers in their parallel composition and the architecture of the matching system. An evaluation of the method is performed on case study examples concerning the matching of four ontology pairs and a comparison with other aggregation methods is given. Additionally, the architecture of the matching system based on our automatic weighted aggregation method is presented.

Automatically Specifying Parallel Composition of Matchers in Ontology Matching Process

Ontology matching plays an important role in the integration of heterogeneous data sources. In order to find semantic correspondences between entities of different ontologies, various matchers can be used. When multiple matchers are integrated into a matching system, the issue of combining these matchers together and determining the importance of every basic matcher arises. In a parallel composition of basic matchers, several matchers are used independently, and then their results are aggregated. In this paper we propose a method for automatically determining weights of basic matchers in their parallel composition. An evaluation of the method is performed on case study examples concerning the matching of three ontology pairs, and a comparison with other aggregation methods is given.

Automating the schema matching process for heterogeneous data warehouses

A federated data warehouse is a logical integration of data warehouses applicable when physical integration is impossible due to privacy policy or legal restrictions. In order to enable the translation of queries in a federated approach, schemas of the federated and the local warehouses must be matched. In this paper we present a procedure that enables the matching process for schema structures specific to the multidimensional model of data warehouses: facts, measures, dimensions, aggregation levels and dimensional attributes. Similarities between warehouse-specific structures are computed by using linguistic and structural comparison, where calculated values are used to create necessary mappings. We present restriction rules and recommendations for aggregation level matching, which builds the most complex part of the process. A software implementation of the entire process is provided in order to perform its verification, as well as to determine the proper selection metric for mapping different multidimensional structures.