The Information Management Group

IMG Seminar 20th June 2012

Pay-as-you-go Ranking of Schema Mappings using Query Logs

Presenter: Ruhaila Maskat

Time 13.00 20th June 2012

Venue: Atlas 1, Kilburn Building

Abstract

Data integration systems typically make use of mappings to capture the relationships between the data resources to be integrated and the integrated representations presented to users. Manual development and maintenance of such mappings is time consuming and thus costly. Pay-as-you-go approaches to data integration support automatic construction of initial mappings, which are generally of rather poor quality, for refinement in the light of user feedback. However, automatic approaches that produce these mappings typically lead to the generation of multiple, overlapping candidate mappings. To present the most relevant set of results to user queries, the mappings have to be ranked. We proposed a ranking technique that uses information from query logs to discriminate among candidate mappings. The technique is evaluated in terms of how quickly stable rankings can be produced, and to investigate how the rankings track query patterns that are skewed towards specific sources.

Diversity of Reason: Equivalence Relations over Description Logic Explanations

Presenter: Samantha Bail

Time 13.00 30th May2012

Venue: Atlas 1, Kilburn Building

Abstract

Given the high expressivity of modern ontology languages, such as OWL, there is the possibility for great diversity in the logical content of ontologies. Informally, this can be seen by the constant evolution of reasoners to deal with new sorts of content and the range of optimisations reasoners need in order to be competitive. More formally, the fact that many naturally occurring entailments have multiple justifications (i.e., minimal entailing subsets) indicates that ontologies often overdetermine their consequences, indicating a diversity in supporting reasons. However, the multiplicity of justifications might be due mostly to diverse material, not formal, grounds for an entailment. That is, the logical form of these multiple reasons could be less diverse than their numbers suggest. In this talk, we introduce and explore several equivalence relations over justifications for entailments of OWL ontologies. These equivalence relations range from strict isomorphism to a looser notions which cover similarities between justifications containing different concept expressions or possibly different numbers of axioms. We present the results of a survey of a corpus of ontologies from the bio-medical domain and find that large numbers of justifications can often be reduced to a significantly smaller set of justifications which are isomorphic with respect to one of the given definitions.

IMG Seminar 10th May 2012

Resilient Sensor Network Query Processing Using Logical Overlays

Presenter: Alan Stokes

Time 11.00 10th May2012 (note unusual day and time)

Venue: Atlas 1, Kilburn Building

Abstract

The typical nodes used in mote-level wireless sensor networks (WSNs) are often brittle and severely resource-contrained. In particular, nodes are often battery-powered, thereby making energy depletion a significant risk. when changes to the connectivity graph occur as a result of node failure, the overall computation may collapse unless it is capable of adapting to the new WSN state. Sensor network query processors (SNQPs) construe a WSN as a distributed, continuous query platform where the streams of sensed values constitute the logical extents of interest. Crucially, they make assumptions about the connectivity graph of the WSN at compile time that are liekly not to hold for the lfietime of the compiled query evalutation plan (QEP) the SNQP generates. Today I will present how we address the problem of extending the lifetime of an evaluating QEP in the event of node failures with a description of how this approach has been implemented in an existing SNQP and show experimental results that indicate a significant increase in the overall lfietime of a query whilst incurring small runtime adaptation costs.

IMG Seminar 18th January 2012

Non-Visual Interaction with Graphs

Presenter: Andy Brown

Time 13.00 18th January 2012

Venue: 2.19, Kilburn Building

Abstract

Node-arc diagrams are widely used, in situations ranging from technical documents to information for the general public - the London Underground map is a classic example.  This is because they are thought to offer several benefits over alternative representations - "a picture is worth a thousand words".  For the blind or visually impaired, however, they are inaccessible; although screen readers offer access to text documents, enabling non-visual access to more
complex, non-linear, information is much more difficult.  In this talk, I shall describe describe how we tackled this problem, exploring the benefits that diagrams offer sighted users, and how annotation can be used to recreate those
benefits in an audio interface.  Example graphs include molecular structure diagrams, logic circuits and family trees.  A demo is currently looking unlikely, but I'll try!

IMG Seminar 19th October 2011

Title: ISWC/CIKM 2011 Papers

Venue: 13.00 Wednesday 19th October 2011 in Atlas 1, Kilburn Building

This seminar is a series of papers that have been accepted for ISWC or CIKM. People are free to come and go and attend those papers that they find interesting.

1:00 pm - Samantha Bail

"The Justificatory Structure of the NCBO BioPortal Ontologies"

Accepted for ISWC2011

Current ontology development tools offer debugging support by presenting justifications for entailments of OWL ontologies. While these minimal subsets have been shown to support debugging and understanding tasks, the occurrence of multiple justifications presents a significant cognitive challenge to users. In many cases even a single entailment may have many distinct justifications, and justifications for distinct entailments may be critically related. However, it is currently unknown how prevalent significant numbers of multiple justifications per entailment are in the field. To address this lack, we examine the justifications from an independently motivated corpus of actively used biomedical ontologies from the NCBO BioPortal. We find that the majority of ontologies contain multiple justifications, while also exhibiting structural features (such as patterns) which can be exploited in order to reduce user effort in the ontology engineering process.

1:30 pm - Eleni Mikroyannidi

"Inspecting regularities in ontology design using clustering"

Accepted for ISWC2011

We propose a novel application of clustering analysis to identify regularities in the usage of entities in axioms within an ontology. We argue that such regularities will be able to help to identify parts of the schemas and guidelines upon which ontologies are often built, especially in the absence of explicit documentation. Such analysis can also isolate irregular entities, thus highlighting possible deviations from the initial design. The clusters we obtain can be fully described in terms of generalised axioms that o er a synthetic representation of the detected regularity. In this paper we discuss the results of the application of our analysis to di erent ontologies and we discuss the potential advantages of incorporating it into future authoring tools.

2:00 pm - Chiara Del Vescovo

"Decomposition and Modular Structure of BioPortal Ontologies"

Accepted for ISWC2011

We present the first large scale investigation into the modular structure of a substantial collection of state-of-the-art biomedical ontologies, namely those maintained in the NCBO BioPortal repository. Using the notion of Atomic Decomposition, we partition BioPortal ontologies into logically coherent subsets (atoms), which are related to each other by a notion of dependency. We analyze various aspects of the resulting structures, and discuss their implications on applications of ontologies. In particular, we describe and investigate the usage of these ontology decompositions to extract modules, for instance, to facilitate matchmaking of semantic Web services in SSWAP (Simple Semantic Web Architecture and Protocol). Descriptions of those services use terms from BioPortal so service discovery requires reasoning with respect to relevant fragments of ontologies (i.e., modules). We present a novel algorithm for extracting modules from decomposed BioPortal ontologies which is able to quickly identify atoms that need to be included in a module to ensure logically complete reasoning. Comparing to existing module extraction algorithms, it has a number of benefits, including improved performance and the possibility to avoid loading the entire ontology into memory. The algorithm is also evaluated on BioPortal ontologies and the results are presented and discussed.

2:30 pm - Rafael Goncalves

"Categorising Logical Differences Between OWL Ontologies"

Accepted for CIKM2011

The analysis of changes between OWL ontologies (in the form of a diff ) is an important service for ontology engineering. A purely syntactic analysis of changes is insufficient to distinguish between changes that have logical impact and those that do not. The current state of the art in semantic diffing ignores logically ineffectual changes and lacks any further characterisation of even significant changes. We present a diff method based on an exhaustive categorisation of effectual and ineffectual changes between ontologies. In order to verify the applicability of our approach we apply it to 88 versions of the National Cancer Institute (NCI) Thesaurus (NCIt), and demonstrate that all categories are realized throughout the corpus. Based on the outcome of the NCIt study we argue that the devised categorisation of changes is helpful for ontology engineers and their understanding of changes carried out between ontologies.