16.4 Managing the Metadata

   

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The specification of the data warehouse is stored in an XML document. This document contains the metadata of the warehouse, including:

1. Information about the JDBC connection for XML data storage

2. Data source URLs

3. View specifications

We chose an XML format for metadata storage because of portability and easy parsing. We present now the DTD validating the warehouse metadata.

16.4.1 Data Warehouse

The root element of the data warehouse specification is declared as follows:

<!-- datawarehouse element -->
<!ELEMENT datawarehouse (connection, source*, view*) >

• "connection" element contains data about the JDBC connection. This data is used to connect the data warehouse manager with the DBMS (MySQL) used to store data of the warehouse.

• "source" element contains data about the XML sources.

• "view" element contains a view definition.

The element describing a source is shown in Listing 16.2.

Listing 16.2 Element Describing an XML Source

<!-- source element -->
<!ELEMENT source EMPTY >
<!ATTLIST source
          id  ID    #REQUIRED
          url CDATA #REQUIRED
>

A "source" element contains two attributes: "id" identifies the source, and "url" gives the XML source URL. Elements describing sources are not encapsulated in pattern elements to easily recognize sources that are used in several patterns.

16.4.2 View Definition

This section describes the part of the DTD that defines a view. The "view" element is described as shown in Listing 16.3.

Listing 16.3 Element Describing a View

<!-- view element -->
<!ELEMENT view (fragment+, join*, result) >
<!ATTLIST view
          id ID #REQUIRED
>

A "view" element is composed of several fragments (one at least), several join conditions, and a result pattern.

Fragment Definition

A "fragment" element describes data to match in one or more XML sources. The part of the DTD shown in Listing 16.4 describes a fragment definition.

Listing 16.4 Element Describing a Fragment

<!-- fragment element -->
<!ELEMENT fragment (pattern+) >
<!ATTLIST fragment
          id ID #REQUIRED
>

A fragment is composed of several pattern subelements (one at least).

The "pattern" element describes data to match in an XML source. A pattern is linked to a source with the "source" attribute, which references a previously defined source. A "pattern" element is composed of a "pattern.node" element indicating the pattern root and one or more "condition" elements. A condition adds a restriction on values of a variable to be matched by the pattern. Listing 16.5 is the part of the DTD describing a pattern definition.

Listing 16.5 Elements Describing a Pattern

<!-- pattern element -->
<!ELEMENT pattern (pattern.node, condition*) >
<!ATTLIST pattern
          id     ID    #REQUIRED
          source IDREF #REQUIRED
>
<!-- pattern node -->
<!ELEMENT pattern.node (pattern.node*) >
<!ATTLIST pattern.node
          name CDATA #REQUIRED
          type CDATA #REQUIRED
          bind CDATA #IMPLIED
>

A pattern is described with "pattern.node" elements that describe the pattern to match in the XML source. For this purpose, a "pattern.node" element contains two attributes: The "type" attribute indicates if the node matches an element or an attribute in the XML source and the "name" attribute indicates the name of the element or attribute to match. The "bind" attribute, if it exists, indicates the variable name that binds the matched element or attribute in the XML source.

The "condition" element allows us to add a condition on the variables defined in the pattern. The part of the DTD shown in Listing 16.6 describes the condition element definition.

Listing 16.6 Element Describing a Condition

<!-- condition node -->
<!ELEMENT condition EMPTY >
<!ATTLIST condition
          left     CDATA #REQUIRED
          operator CDATA #REQUIRED
          right    CDATA #REQUIRED
>

Join Definition

A "join" element contains the join condition between the fragments defined in the view. The part of the DTD shown in Listing 16.7 describes the join element definition.

Listing 16.7 Element Describing a Join

<!-- join node -->
<!ELEMENT join EMPTY >
<!ATTLIST join
          leftfragment  IDREF #REQUIRED
          leftvariable  CDATA #REQUIRED
          rightfragment IDREF #REQUIRED
          rightvariable CDATA #REQUIRED
>

The "join" element contains four attributes indicating fragments and variables defining the join condition. The "leftfragment" and "rightfragment" attributes are IDREF attributes referencing the left and right fragments to join. The "leftvariable" and "rightvariable" contain the names of the variables of the left and right fragments used in the join condition.

Result Definition

Finally, the "result" element contains the definition of the view result pattern (see Listing 16.8).

Listing 16.8 Elements Describing a Result and Grouping Constraints

<!-- result -->
<!ELEMENT result (result.node, groupby*) >
<!-- result node -->
<!ELEMENT result.node (result.node*) >
<!ATTLIST result.node
          name CDATA #REQUIRED
          type CDATA #REQUIRED
>
<!-- group by -->
<!ELEMENT groupby EMPTY >
<!ATTLIST groupby
          variable CDATA #REQUIRED
>

The "result" element contains the description of the view result structure. It is composed of a "result.node" element containing the result pattern and zero or more "groupby" elements indicating how result data will be organized.

16.4.3 Mediated Schema Definition

The main role of a data warehouse is to provide integrated and uniform access to heterogeneous and distributed data. For this purpose, a mediated schema is provided to users on which they can formulate their queries. Metadata are used to create this schema. In the following, we will present how this schema is generated.

To provide an integrated view of heterogeneous sources, the data warehouse is considered as an entire XML document, containing the result of all the views. The fragment of DTD describing the data warehouse (with "N" views) is as follows:

<!ELEMENT datawarehouse (view1, view2,  . . . , viewN) >

The view model allows us to generate a DTD on a view specification. This DTD is defined with the result pattern and could possibly be completed with the source definition. The generated DTD for the view that is specified in Listing 16.1 is shown in Listing 16.9.

Listing 16.9 DTD Generated for the View in Listing 16.1

<!ELEMENT authorspublications (author*) >
<!ELEMENT author (title+) >
<!ATTLIST author name CDATA #REQUIRED >
<!ELEMENT title (#PCDATA) >

The root of the view result is an element, of which the type is the view name "authorspublications". The "author" element is composed of one or more "title" elements, because of the group-by clause, and has one attribute containing the author's name.

The mediated schema is aimed at querying the XML data in the warehouse. Currently, the query manager evaluates the XML views from the database system. In the future, the query manager capabilities will be extended to enable the processing of XPath queries with a DTD-driven tool.

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Top Title TOC Preface P.1 What Is XML? P.2 XML Concepts P.3 XML-Related Technologies P.4 XML Data Management P.5 How This Book Is Organized P.6 Who Should Read This Book P.7 Resources Acknowledgments Chapter 8 Chapter 12 Chapter 13 Chapter 14 Chapter 19 Part I: What Is XML? Chapter 1. Information Modeling with XML 1.1 Introduction 1.2 XML as an Information Domain 1.3 How XML Expresses Information 1.4 Patterns in XML 1.5 Common XML Information-Modeling Pitfalls 1.6 A Very Simple Way to Design XML 1.7 Conclusion Part II: Native XML Databases Chapter 2. Tamino-Software AG's Native XML Server 2.1 Introduction 2.2 Tamino Architecture and APIs 2.3 XML Storage 2.4 Querying XML 2.5 Tools 2.6 Full Database Functionality 2.7 Conclusion Chapter 3. eXist Native XML Database 3.1 Introduction 3.2 Features 3.3 System Architecture Overview 3.4 Getting Started 3.5 Query Language Extensions 3.6 Application Development 3.7 Technical Background 3.8 Conclusion Chapter 4. Embedded XML Databases 4.1 Introduction 4.2 A Primer on Embedded Databases 4.3 Embedded XML Databases 4.4 Building Applications for Embedded XML Databases 4.5 Conclusion Part III: XML and Relational Databases Chapter 5. IBM XML-Enabled Data Management Product Architecture & Technology 5.1 Introduction 5.2 Product and Technology Offering Summaries 5.3 Current Architecture and Technology 5.4 Future Architecture and Technology 5.5 Conclusion Notices Chapter 6. Supporting XML in Oracle9i 6.1 Introduction 6.2 Storing XML as CLOB 6.3 XMLType 6.4 Using XSU for Fine-Grained Storage 6.5 Building XML Documents from Relational Data 6.6 Web Access to the Database 6.7 Special Oracle Features 6.8 Conclusion Chapter 7. XML Support in Microsoft SQL Server 2000 7.1 Introduction 7.2 XML and Relational Data 7.3 XML Access to SQL Server 7.4 Serializing SQL Query Results into XML 7.5 Providing Relational Views over XML 7.6 SQLXML Templates 7.7 Providing XML Views over Relational Data 7.8 Conclusion Chapter 8. A Generic Architecture for Storing XML Documents in a Relational Database 8.1 Introduction 8.2 System Architecture 8.3 The Data Model 8.4 Creating the Database 8.5 Connecting to the Repository 8.6 Uploading XML Documents 8.7 Querying the Repository 8.8 Further Enhancements 8.9 Conclusion Chapter 9. An Object-Relational Approach to Building a High-Performance XML Repository 9.1 Introduction 9.2 Overview of XML Use-Case Scenario 9.3 High-Level System Architecture 9.4 Detailed Design Descriptions 9.5 Conclusion Part IV: Applications of XML Chapter 10. Knowledge Management in Bioinformatics 10.1 Introduction 10.2 A Brief Molecular Biology Background 10.3 Life Sciences Are Turning to XML to Model Their Information 10.4 A Genetic Information Model 10.5 NeoCore XMS* 10.6 Integration of BLAST into NeoCore XMS Conclusion Chapter 11. Case Studies of XML Used with IBM DB2 Universal Database 11.1 Introduction 11.2 Case Study 1: "Our Most Valued Customers Come First" 11.3 Case Study 2: "Improve Cash Flow" 11.4 Conclusion Notices Chapter 12. The Design and Implementation of an Engineering Data Management System Using XML and J2EE 12.1 Introduction 12.2 Background and Requirements 12.3 Overview 12.4 Design Choices 12.5 Future Directions 12.6 Conclusion Chapter 13. Geographical Data Interchange Using XML-Enabled Technology within the GIDB System 13.1 Introduction 13.2 GIDB METOC Data Integration 13.3 GIDB Web Map Service Implementation 13.4 GIDB GML Import and Export 13.5 Conclusion Chapter 14. Space Wide Web by Adapters in Distributed Systems Configuration from Reusable Components 14.1 Introduction 14.2 Advanced Concept Description: The Research Problem 14.3 Integration of Components with Architecture 14.4 Example 14.5 Future Generation NASA Institute for Advanced Concepts, Space Wide Web Research, and Boundaries 14.6 Advanced Concept Development 14.7 Conclusion Chapter 15. XML as a Unifying Framework for Inductive Databases 15.1 Introduction 15.2 Past Work 15.3 The Proposed Data Model: XDM 15.4 Benefits of XDM 15.5 Toward Flexible and Open Systems 15.6 Related Work 15.7 Conclusion Chapter 16. Designing and Managing an XML Warehouse 16.1 Introduction 16.2 Architecture 16.3 Data Warehouse Specification 16.4 Managing the Metadata 16.5 Storage and Management of the Data Warehouse 16.6 DAWAX: A Graphic Tool for the Specification and Management of a Data Warehouse 16.7 Related Work 16.8 Conclusion Part V: Performance and Benchmarks Chapter 17. XML Management System Benchmarks 17.1 Introduction 17.2 Benchmark Specification 17.3 Benchmark Data Set 17.4 Existing Benchmarks for XML 17.5 Conclusion Chapter 18. The Michigan Benchmark: A Micro-Benchmark for XML Query Performance Diagnostics 18.1 Introduction 18.2 Related Work 18.3 Benchmark Data Set 18.4 Benchmark Queries 18.5 Using the Benchmark 18.6 Conclusion Chapter 19. A Comparison of Database Approaches for Storing XML Documents 19.1 Introduction 19.2 Data Models for XML Documents 19.3 Databases for Storing XML Documents 19.4 Benchmarking Specification 19.5 Test Results 19.6 Related Work 19.7 Summary Chapter 20. Performance Analysis between an XML-Enabled Database and a Native XML Database 20.1 Introduction 20.2 Related Work 20.3 Methodology 20.4 Database Design 20.5 Discussion 20.6 Experiment Result 20.7 Conclusion Chapter 21. Conclusion References Contributors Editors Chapter 1: Information Modeling with XML Chapter 2: Tamino-Software AG's Native XML Server Chapter 3: eXist Native XML Database Chapter 4: Embedded XML Databases Chapter 5: IBM XML-Enabled Data Management Product Architecture and Technology Chapter 6: Supporting XML in Oracle9i Chapter 7: XML Support in Microsoft SQL Server 2000 Chapter 8: A Generic Architecture for Storing XML Documents in a Relational Database Chapter 9: An Object-Relational Approach to Building a High-Performance XML Repository Chapter 10: Knowledge Management in Bioinformatics Chapter 11: Case Studies of XML Used with IBM DB2 Universal Database Chapter 12: The Design and Implementation of an Engineering Data Management System Using XML and J2EE Chapter 13: Geographical Data Interchange Using XML-Enabled Technology within the GIDB System Chapter 14: Space Wide Web by Adapters in Distributed Systems Configuration from Reusable Components Chapter 15: XML as a Unifying Framework for Inductive Databases Chapter 16: Designing and Managing an XML Warehouse Chapter 17: XML Management System Benchmarks Chapter 18: The Michigan Benchmark: A Micro-Benchmark for XML Query Performance Diagnostics Chapter 19: A Comparison of Database Approaches for Storing XML Documents Chapter 20: Performance Analysis between an XML-Enabled Database and a Native XML Database Remember the name: eTutorials.org Copyright eTutorials.org 2008-2023. 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