Mong Li Lee

XClust: clustering XML schemas for effective integration

It is increasingly important to develop scalable integration techniques for the growing number of XML data sources. A practical starting point for the integration of large numbers of Document Type Definitions (DTDs) of XML sources would be to first find clusters of DTDs that are similar in structure and semantics. Reconciling similar DTDs within such a cluster will be an easier task than reconciling DTDs that are different in structure and semantics as the latter would involve more restructuring. We introduce XClust, a novel integration strategy that involves the clustering of DTDs. A matching algorithm based on the semantics, immediate descendents and leaf-context similarity of DTD elements is developed. Our experiments to integrate real world DTDs demonstrate the effectiveness of the XClust approach.

Quantitative and qualitative retinal microvascular characteristics and blood pressure.

Objective The present study examined the effects of blood pressure on a spectrum of quantitative and qualitative retinal microvascular signs. Methods Retinal photographs from the Singapore Malay Eye Study, a population-based cross-sectional study of 3280 (78.7% response) persons aged 40–80 years, were analyzed. Quantitative changes in the retinal vasculature (branching angle, vascular tortuosity, fractal dimension, and vascular caliber) were measured using a semi-automated computer-based program. Qualitative signs, including focal arteriolar narrowing (FAN), arteriovenous nicking (AVN), opacification of the arteriolar wall (OAW), and retinopathy (e.g., microaneurysms, retinal hemorrhages), were assessed from photographs by trained technicians. After excluding persons with diabetes and ungradable photographs, 1913 persons provided data for this analysis. Results In multivariable linear regression models controlling for age, sex, BMI, use of antihypertensive medication, and other factors, retinal arteriolar branching asymmetry ratio, arteriolar tortuosity, venular tortuosity, fractal dimension, arteriolar caliber, venular caliber, FAN, AVN, and retinopathy were independently associated with mean arterial blood pressure. In contrast, arteriolar/venular branching angle, venular branching asymmetry ratio and OAW were not related to blood pressure. Retinal arteriolar caliber (sβ = −0.277) and FAN (sβ = 0.170) had the strongest associations with mean arterial blood pressure, and higher blood pressure levels were associated with increasing number of both quantitative and qualitative retinal vascular signs (P trend <0.001). Conclusion Elevated blood pressure is associated with a spectrum of quantitative and qualitative retinal vascular signs, with the number of signs increasing with higher blood pressure levels.

Designing Functional Dependencies for XML

Functional dependencies are an integral part of database theory and they form the basis for normalizing relational tables up to BCNF. With the increasing relevance of the data-centric aspects of XML, it is pertinent to study functional dependencies in the context of XML, which will form the basis for further studies into XML keys and normalization. In this work, we investigate the design of functional dependencies in XML databases. We propose FDXML, a notation and DTD for representing functional dependencies in XML. We observe that many databases are hierarchical in nature and the corresponding nested XML data may inevitably contain redundancy. We develop a model based on FDXML to estimate the amount of data replication in XML data. We show how functional dependencies in XML can be verified with a single pass through the XML data, and present supporting experimental results. A platform-independent framework is also drawn up to demonstrate how the techniques proposed in this work can enrich the semantics of XML.

Resolving Structural Conflicts in the Integration of XML Schemas: A Semantic Approach

While the Internet has facilitated access to information sources, the task of scalable integration of these heterogeneous data sources remains a challenge. The adoption of the eXtensible Markup Language (XML) as the standard for data representation and exchange has led to an increasing number of XML data sources, both native and non-native. Recent integration work has mainly focused on developing matching techniques to find equivalent elements and attributes among the different XML sources. In this paper, we introduce a semantic approach to resolve structural conflicts in the integration of XML schemas. We employ a data model called the ORA-SS (Object-Relationship-Attribute Model for Semi-Structured Data) to capture the implicit semantics in an XML schema. We present a comprehensive algorithm to integrate XML schemas. Compared to existing methods, our algorithm adopts an n-nary integration strategy that takes into account the data semantics, importance of a source, and how the majority of the sources model their data when resolving structural conflicts such as attribute/object class conflict and ancestor-descendant conflict. Further, redundant object classes and transitive relationship sets are removed to obtain a more concise integrated schema.

Resolving Constraint Conflicts in the Integration of Entity-Relationship Schemas

In this work, we address the problem of constraint conflicts while integrating the conceptual schemas of multiple autonomous databases modeled using the Entity Relationship (ER) approach. This paper presents a detailed framework to resolve three types of constraint conflicts, domain constraint conflicts, attribute constraint conflicts and relationship constraint conflicts. There are two types of domain constraint conflict, convertible and inconvertible. We distinguish two types of convertible domain constraints conflict, reversible and irreversible, and present an algorithm to resolve domain constraint conflicts. We identify six factors that can contribute to conflict in attribute constraints: imprecise constraint design, domain mismatch, incomplete information, imprecise semantics, value inconsistency and set relation between object types. In relationship constraint conflict resolution, we examine the set relation between equivalent relationship sets and the functional dependencies that hold in these relationship sets. Our conflict resolution approach does not assume that equivalent entity types or relationship sets in two schemas model exactly the same set of instances in the real world. Furthermore, our approach enforces the most precise constraints and enables the retrieval of all the data in the local databases via the integrated schema.

FlowMiner: finding flow patterns in spatio-temporal databases

The widespread use of spatio-temporal databases and applications has fuelled an urgent need to discover interesting time and space patterns in such databases. While much work has been done in discovering time/sequence patterns or spatial patterns, discovering of patterns involving both time and space dimensions is still in its infancy, We introduce the concept of flow patterns. Flow patterns are intended to describe the change of events over space and time. These flow patterns are useful to the understanding of many real-life applications. We present a disk-based algorithm, FlowMiner, which utilizes temporal relationships and spatial relationships amid events to generate flow patterns. Our performance study shows that FlowMiner is both scalable and efficient. Experiments on real-life datasets also reveal interesting flow patterns.

Lens opacity and refractive influences on the measurement of retinal vascular fractal dimension

Acta Ophthalmol. 2010: 88: e234–e240

Resolving Structural Conflicts in the Integration of Entity Relationship Schemas

Schema integration is essential to define a global schema that describes all the data in existing databases participating in a distributed or federated database management system. This paper describes a different approach to integrate two Entity-Relationship (ER) schemas. We focus on the resolution of structural conflicts, that is, when related real world concepts are modelled using different constructs in different schemas. Unlike previous works, our approach only needs to resolve the structural conflict between an entity type in one schema and an attribute in another schema and the other structural conflicts are automatically resolved. We have an algorithm to transform an attribute in one schema into an equivalent entity type in another schema without any loss of semantics or functional dependencies which previous approaches have not considered.

Designing Valid XML Views

Existing systems for XML views only support selection operation applied in the views and cannot validate views. In this paper, we propose a systematic approach to design valid XML views. First, we transform the semistructured XML source documents into a semantically rich Object-Relationship-Attribute model designed for SemiStructured data (ORA-SS). Second, we enrich the ORA-SS diagram with semantics such as participation constraints of object classes and distinguishing between attributes of object classes and relationship types, which cannot be expressed in the XML document. Third, we use the additional semantics to develop a set of rules to guide the design of valid XML views. We identify four transformation operations for creating XML views, namely, selection, projection, join and swap operation. Finally, we develop a comprehensive algorithm that checks for the validity of XML views constructed by applying the four operations.