Wang-chiew Tan

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Papers by Wang-chiew Tan

Data Provenance: Some Basic Issues

Lecture Notes in Computer Science, 2000

The ease with which one can copy and transform data on the Web, has made it increasingly difficul... more The ease with which one can copy and transform data on the Web, has made it increasingly difficult to determine the origins of a piece of data. We use the term data provenance to refer to the process of tracing and recording the origins of data and its movement between databases. Provenance is now an acute issue in scientific databases where it is central to the validation of data. In this paper we discuss some of the technical issues that have emerged in an initial exploration of the topic.

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Preference-aware integration of temporal data

Proceedings of the VLDB Endowment, 2014

Federation in Cloud Data Management: Challenges and Opportunities

IEEE Transactions on Knowledge and Data Engineering, 2014

MapMerge: correlating independent schema mappings

One of the main steps towards integration or exchange of data is to design the mappings that desc... more One of the main steps towards integration or exchange of data is to design the mappings that describe the (often complex) relationships between the source schemas or formats and the desired target schema. In this paper, we introduce a new operator, called Map-Merge, that can be used to correlate multiple, independently designed schema mappings of smaller scope into larger schema mappings. This allows a more modular construction of complex mappings from various types of smaller mappings such as schema correspondences produced by a schema matcher or pre-existing mappings that were designed by either a human user or via mapping tools. In particular, the new operator also enables a new "divideand-merge" paradigm for mapping creation, where the design is divided (on purpose) into smaller components that are easier to create and understand, and where MapMerge is used to automatically generate a meaningful overall mapping. We describe our MapMerge algorithm and demonstrate the feasibility of our implementation on several real and synthetic mapping scenarios. In our experiments, we make use of a novel similarity measure between two database instances with different schemas that quantifies the preservation of data associations. We show experimentally that MapMerge improves the quality of the schema mappings, by significantly increasing the similarity between the input source instance and the generated target instance.

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The complexity of data exchange

Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '06, 2006

Data exchange is the problem of transforming data structured under a source schema into data stru... more Data exchange is the problem of transforming data structured under a source schema into data structured under a target schema in such a way that all constraints of a schema mapping are satisfied. At the heart of data exchange, lies a basic decision problem, called the existence-of-solutions problem: given a source instance, is there a target instance that satisfies the constraints of the schema mapping at hand? Earlier work showed that for schema mappings specified by embedded implicational dependencies, this problem is solvable in polynomial time, assuming that (1) the schema mapping is kept fixed and (2) the constraints of the schema mapping satisfy a certain structural condition, called weak acyclicity.

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On propagation of deletions and annotations through views

Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '02, 2002

We study two classes of view update problems in relational databases. We are given a source datab... more We study two classes of view update problems in relational databases. We are given a source database S, a monotone query Q, and the view Q(S) generated by the query. The first problem that we consider is the classical view deletion problem where we wish to identify a minimal set T of tuples in S whose deletion will eliminate a given tuple t from the view. We study the complexity of optimizing two natural objectives in this setting, namely, find T to minimize the side-effects on the view, and the source, respectively. For both objective functions, we show a dichotomy in the complexity. Interestingly, the problem is either in P or is NP-hard, for queries in the same class in either objective function.

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QUICK: graphical user interface to multiple databases

Proceedings of 7th International Conference and Workshop on Database and Expert Systems Applications: DEXA 96, 1996

Formulating queries to access multiple databases can be a formidable task, especially when many t... more Formulating queries to access multiple databases can be a formidable task, especially when many terms from various databases and complex constraints are involved. To specify a multidatabase query, the user usually has to search through documents for exact database terms and learn the multidatabase language. This report presents QUICK (QUery Interface to CPL-Kleisli), a graphical user interface to multiple databases. CPL (Collection Programming Language) is a high-level multidatabase language built on top of an open query system Kleisli. QUICK allows users to handle overwhelming information from di erent data sources in an intuitive and uniform manner. The query speci cation is reduced to specifying user's terms in his/her own world, selecting paths and specifying constraints in a graph. Through the terms entered by the user, QUICK is able to reduce the scope of the views and paths to only those that are relevant to answering the user's query. Furthermore, QUICK is able to automatically generate a CPL query that corresponds to the user's intent. Additional graphical functions are provided for the user to ne-tune the query generated.

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Fusing data management services with file systems

Proceedings of the 4th Annual Workshop on Petascale Data Storage - PDSW '09, 2009

File systems are the backbone of large-scale data processing for scientific applications. Motivat... more File systems are the backbone of large-scale data processing for scientific applications. Motivated by the need to provide an extensible and flexible framework beyond the abstractions provided by API libraries for files to manage and analyze large-scale data, we are developing Damasc, an enhanced file system where rich data management services for scientific computing are provided as a native part of the file system. This paper presents our vision for Damasc, a performant file system that would allow scientists or even casual users to pose declarative queries and updates over views of underlying files that are stored in their native bytestream format. In Damasc, a configurable layer is added on top of the file system to expose the contents of files in a logical data model through which views can be defined and used for queries and updates. The logical data model and views are leveraged to optimize access to files through caching and selforganizing indexing. In addition, provenance capture and analysis to file access is also built into Damasc. We describe the salient features of our proposal and discuss how it can benefit the development of scientific code.

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Why and Where: A Characterization of Data Provenance

Lecture Notes in Computer Science, 2001

Abstract. With the proliferation of database views and curated data- bases, the issue of data pro... more

On computing functions with uncertainty

Proceedings of the twentieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '01, 2001

ABSTRACT We study the problem of computing a function f x1; :::; xn given that the actual values ... more

Comparing and evaluating mapping systems with STBenchmark

Proceedings of the VLDB Endowment, 2008

Schema mappings are fundamental building blocks in many information integration applications. Des... more Schema mappings are fundamental building blocks in many information integration applications. Designing mappings is a timeconsuming process and for that reason many mapping systems have been developed to assist in the task of designing mappings. However, to the best of our knowledge, a benchmark for comparing and evaluating these systems has not yet been developed. We demonstrate STBenchmark, a benchmark that we have developed for evaluating mapping systems. Our demonstration will showcase the different aspects of mapping systems that STBenchmark evaluates, highlight the results of our comparison and evaluation of four mapping systems, as well as make a case for the need for a standard specification input mechanism to mapping systems in order to make progress towards the development of a uniform testbed or repository for schema mappings and data exchange tasks.

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Minimizing Uncertainty in Crowd Data Sourcing

Query Answering over Incomplete and Uncertain RDF

Correlating independent schema mappings

A New Framework for Designing Schema Mappings

Composite simulation modeling and analysis

Synchronization of time between different simulation models

Provenance

In Search of Elegance in the Theory and Practice of Computation: Essays Dedicated to Peter Buneman

Curated databases

Proceedings of the twenty-seventh ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '08, 2008

Curated databases are databases that are populated and updated with a great deal of human effort.... more Curated databases are databases that are populated and updated with a great deal of human effort. Most reference works that one traditionally found on the reference shelves of libraries -dictionaries, encyclopedias, gazetteers etc.are now curated databases. Since it is now easy to publish databases on the web, there has been an explosion in the number of new curated databases used in scientific research. The value of curated databases lies in the organization and the quality of the data they contain. Like the paper reference works they have replaced, they usually represent the efforts of a dedicated group of people to produce a definitive description of some subject area.

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