Browsing by Author "Gillian DOBBIE"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    ORA-SS: An Object-Relationship-Attribute Model for Semi-Stractured Data
    (2000-12-01T00:00:00Z) Gillian DOBBIE; Xiaoying WU; Tok Wang LING; Mong Li LEE
    Semi-structured data is becoming increasingly important with the introduction of XML and related languages and technologies. The recent shift from DTDs (document type definitions) to XML-Schema for XML data highlights the importance of a schema definition for semi-structured data applications. At the same time, there is a move to extend semi-structured data models to express richer semantics. In this paper we propose a semantically rich data model for semi-structured data, ORA-SS (Object-Relationship-Attribute model for Semi-Structured data). ORA-SS not only reflects the nested structure of semi-structured data, but it also distinguishes between objects, relationships and attributes. It is possible to specify the degree of n-ary relationships and indicate if an attribute is an attribute of a relationship or an attribute of an object. Such information is lacking in existing semi-structured data models, and is essential information for designing an efficient and non-redundant storage organization for semi-structured data.
  • No Thumbnail Available
    Item
    Practical approach to selecting data warehouse views using data dependencies
    (2000-07-01T00:00:00Z) Gillian DOBBIE; Tok Wang LING
    Data warehouses integrate information from heterogeneous sources and enable efficient analysis of the information. The two main characteristics of data warehouses are the huge volumes of data they store and the requirement of fast access to the data. Because of the huge volumes of data, simple search techniques are not sufficient. Materialized views in data warehouses are typically complicated, based on many tables, often containing summarized information, but are very important for improving access to the data. Because data warehouses are expected to contain current information, it is also important that the data warehouse, and the views, can be easily updated periodically. The selection of materialized views changes over time, with new materialized views created and old ones dropped. So, the selection of materialized views is crucial. Most research to date has treated the selection of materialized views as an optimization problem with respect to the cost of view maintenance and/or with respect to the cost of queries. In this paper, we consider practical aspects of data warehousing. We identify problems with the star and snowflake schema and suggest solutions, that we call enhanced star schema and enhanced snowflake schema. We also identify practical problems that may arise during view design and suggest heuristics based on data dependencies that can be used to measure if one set of views is better than another set of views, or used to improve a set of views with respect to speed of access.
  • No Thumbnail Available
    Item
    XOO7: Applying OO7 Benchmark to XML Query Processing Tools
    (2001-06-01T00:00:00Z) Stephane BRESSAN; Gillian DOBBIE; Zoe LACROIX; Mong Li LEE; Ying Guang LI; Ullas NAMBIAR; Bimlesh WADHWA
    If XML is to play the critical role of the lingua franca for Internet data interchange that many predict, it is necessary to start designing and adopting benchmarks allowing the comparative performance analysis of the tools being developed and proposed. The effectiveness of existing XML query languages has been studied by many who focused on the comparison of linguistic features, implicitly reflecting the fact that most XML tools exist only on paper. In this paper, with a focus on efficiency and concreteness, we propose a pragmatic first step toward the systematic benchmarking of XML query processing platforms with an initial focus on the data (versus document) point of view. We propose XOO7, an XML version of the OO7 benchmark. We discuss the applicability of XOO7, its strengths, limitations and the extensions we are considering. We illustrate its use by presenting and discussing the performance comparison against XOO7 of three different query processing platforms for XML.
  • No Thumbnail Available
    Item
    XTree: A Declarative Query Language for XML Documents
    (2005-01-11T07:45:30Z) Zhuo CHEN; Tok Wang LING; Mengchi LIU; Gillian DOBBIE
    XML is becoming prevalent in data presentation and data exchange on the internet. One important issue in the XML research community is how to query XML documents to extract and restructure information. Currently, XQuery based on XPath is the most promising standard. In this paper, we discuss limitations of XPath and XQuery, and propose a generalization of XPath called XTree that overcomes these limitations. Using XTree, multiple variable bindings can be instantiated in one expression; and XTree expressions, which represent a tree rather than a path, can be used in both the querying part and the result construction part of a query. Based on XTree, we develop an XTree query language, which is more compact and convenient to use than XQuery, and supports common query operations such as join, negation, grouping, and recursion in a direct way. We describe an algorithm that converts XTree query scripts to XQuery scripts. This algorithm provides not only a means of executing queries written in XTree query language but also highlights differences between the two query languages.