數位圖書館 – XML 系統應用

數位圖書館 – XML 系統應用

Jian-hua Yeh (葉建華 )

真理大學資訊科學系助理教授[email protected]

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Outline

• XML language introduction

• XML server architecture

• XML query language design issues

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XML Introduction

• What is XML?

• Why XML?

• The XML power

• XML and the enterprise

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What is XML?

• Proposed by W3C at the end of 1996

• SGML-derived

• A meta-language for new tagging language

• XML1.0 Recommendation released at Feb. 1998

• Supporting

– Sun, Microsoft, Netscape, Adobe, ArborText, etc.

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What is XML? (2)

• eXtensible Markup Language

• Tag-based

• Open and cross-platform

• Structural data representation

• As data and as document

• Suitable for data exchange

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<?xml version="1.0"?> <invoicecollection> <invoice> <customer> Wile E. Coyote, Death Valley, CA </customer> <annotation> Customer asked that we guarantee return rights if these items should fail in desert conditions. This was approved by Marty Melliore, general manager. </annotation> <entries n=2> <entry quantity=2 total_price="134.00"> <product maker="ACME" prod_name="screwdriver" price="80.00"/> </entry> <entry quantity=1 total_price="20.00"> <product maker="ACME" prod_name="power wrench" price="20.00"/> </entry> </entries> </invoice> <invoice> <customer> Camp Mertz </customer> <entries n=2> <entry quantity=2 total_price="32.00"> <product maker="BSA" prod_name="left-handed smoke shifter" price="16.00"/> </entry> <entry quantity=1 total_price="13.00"> <product maker="BSA" prod_name="snipe call" price="13.00"/> </entry> </entries> </invoice> </invoicecollection>

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Why XML?

• HTML is not enough, no structural data handling capability

• Recommended by W3C, an open standard

• The push of enterprise integration

• To break the stovepipe system, from vertical to horizontal

• The need of B2B, B2C integration

• Platform independent

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Traditional Data Exchange Handling

• Private protocol for stovepipe system

• Open standard for data exchange

– RPC

– RMI

– CORBA

– COM

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New Strategy of Data Exchange

• Text-based

• Tag-oriented

• Self-descriptive

• Data Type Definition

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XML Details

• Components

– DTD

– XML content

• Processing models

– Event driven model: SAX

• A document is treated as a set of events

– Structural model: DOM

• A document is represented as a tree structure

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XML Server Introduction

• Why XML server?

– Comply with enterprise service model: client/middle/EIS structure

• Common components can consists of 3rd party software vendors

– XML parser, XSL processor, etc.

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XML Server Architecture

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XML Server Architecture (2)

• Key aspects

– Client

• PDA, browser, Web server, other XML server, etc.

– Communication protocol

• Email, HTTP, FTP, EJB, RMI, IIOP, COM, etc.

– Key services

– Data object

• Relational database, object data source, etc.

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XML Server Components

• Client

• Communication service

• Document handler

• Data object access module

• XML core service

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An Operation Example

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XML support in Java technology

• XML processing

• Data binding

• Remote communication

• Service registry

• Messaging

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Java for XML Processing

• JAXP (Java API for XML Processing)

– SAX (Simple API for XML) parser

• Event-based XML parsing

– DOM (Document Object Model) parser

• Model-based XML parsing

– XSLT (XML Stylesheet Language for Transformations) processor

• Support SAX, DOM, stream-specific processing

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Java for XML Data Binding

• JAXB (Java Architecture for XML Binding)

– Schema-based

– Validation

– Representing XML content

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Java for XML Communication

• JAX-RPC (Java API for XML-based RPC)

– RPC-based Web service

– SOAP-based (Simple Object Access Protocol)

– Discoverable by using JAXR (*later*)

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Java for XML Registries

• JAXR (Java API for XML Registries)

– Service registration

– Service lookup

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Java for XML Messaging

• JAXM (Java API for XML Messaging)

– Message provider

• SAAJ (SOAP with Attachments API for Java)

– Message population with attachment

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XML Processing, How?

• Locating: XPath

• Querying: XQL, XQuery

• Storage: XMLDB

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What is XPath?

• W3C standard

• A syntax for defining parts of an XML document

• Uses paths to define XML elements

• Defines a library of standard functions

• A major element in XSLT

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Sample XML

<?xml version="1.0" encoding="ISO-8859-1"?><catalog> <cd country="USA"> <title>Empire Burlesque</title> <artist>Bob Dylan</artist> <price>10.90</price> </cd> <cd country="UK"> <title>Hide your heart</title> <artist>Bonnie Tyler</artist> <price>9.90</price> </cd> <cd country="USA"> <title>Greatest Hits</title> <artist>Dolly Parton</artist> <price>9.90</price> </cd></catalog>

• Path

– /catalog/cd/price

• Function

– /catalog/cd[price>10.80]

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XPath: The Syntax

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Path Syntax: Locating Nodes

• /catalog/cd/price

• //cd

• /catalog/cd/*

• /catalog/*/price

• /*/*/price

• //*


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Path Syntax: Selecting Branches

• /catalog/cd[1]

• /catalog/cd[last()]

• /catalog/cd[price]

• /catalog/cd[price=10.90]

• /catalog/cd[price=10.90]/

price


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Path Syntax: Selecting Several Paths• /catalog/cd/title |

/catalog/cd/artist

• //title | //artist

• //title | //artist | //price


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Path Syntax: Selecting Attributes• //@country

• //cd[@country]

• //cd[@*]

• //cd[@country='UK']


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XPath: Location paths

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Formal Syntax

• axisname::nodetest[predicate]

– child::price[price=9.90]

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Axes and Node Tests

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Abbreviated Syntax

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Location Paths Examples

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XPath: The expressions

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Expression Types

• Numerical expressions

• Equality expressions

• Relational expressions

• Boolean expressions

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Numerical Expressions

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Equality Expressions

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Relational Expressions

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Boolean Expressions

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XPath: The functions

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XPath Function Library

• Node Set Functions

• String Functions

• Number Functions

• Boolean Functions

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Node Set Functions

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String Functions

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Number Functions

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Boolean Functions

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XQL: XML Query Language

• XQL problem domains

• Queries, search contexts, and result sets

• Result sets vs. result documents

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XQL Introduction

• Developers

– Texcel, webMethods, Microsoft

• Traditional query processing

• Features of XML documents

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Traditional Query Processing

• Structured query

– For relational database

– For object-oriented database

• Unstructured full-text query

– For text documents

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Features of XML Documents

• As documents

• As data sources

• With structure feature

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XQL Problem Domains

• Queries within a single document(in a browser or editor)

• Queries in collections of documents(document assembly in an XML repository)

• Addressing within or across documents

• XSL Patterns

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The Role of a Query Language

• Different problem domain has different input/output and processing model

• Common thing

– assertion(name,content,value,relationship)

• Tradeoff

– design separate query language for each problem domain

– a general-purpose query language for all problem domains

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SQL vs. XQL

SQL XQL

The database is a set of tables. The database is a set of one or more XML documents.

Queries are done in SQL, a query language that uses tables as a basic model.

Queries are done in XQL, a query language that uses the structure of XML as a basic model.

The FROM clause determines the tables which are examined by the query.

A query is given a set of input nodes from one or more documents, and examines those nodes and their descendants.

The result of a query is a table containing a set of rows.

The result of a query is a set of XML document nodes, which can be wrapped in a root node to create a well-formed XML document.

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Simple Query Example

Search Context

<novel> <front> <title>The Heart of Darkness</title> <author>Joseph Conrad</author> </front></novel>

Query novel

Result Set

<novel> <front> <title>The Heart of Darkness</title> <author>Joseph Conrad</author> </front></novel>

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Why result documents?

• An XML document is easily parsed with a standard XML parser, so it can be transmitted as a single ASCII stream and parsed by the receiving application.

• An XML document can be displayed in a standard XML browser.

• An XML document can be stored in an XML repository.

• An XML document can be passed on to an XSL processor to perform transformations or do formatting.

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XML Database

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What is Native XML Database?

• Defines a (logical) model for an XML document

– The database is specialized for storing XML data

• Has an XML document as its fundamental unit of (logical) storage

– Documents in, documents out

• Is not required to have any particular underlying physical storage model

– May not actually be a standalone database at all

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Native XML Database Features

• XML storage

• Collections

– Allow you to query and manipulate those documents as a set

• Queries

– XPath, XQL

• Updates

– Update portions of documents (XUpdate)

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Native XML Database Products

• eXist: proprietary/relational

• ozone: object-oriented

• Tamino: proprietary/relational

• Xindice: proprietary

• X-Hive: object-oriented/relational