Xml Intro

XML for Libraries Roy Tennant eScholarship California Digital Library escholarship.cdlib.org

Introduction • Goal: introduce you to XML, explain what it can do in general terms, and highlight particular uses • Caveat: you will not learn enough to do it without further study

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Outline • • • • •

Introduction to XML Serving XML to the Web Case Studies Tips & Advice Resources

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Introduction to XML • Extensible Markup Language • A method of creating and using tags to identify the structure and contents of a document — not how it should be displayed • The tags used can be arbitrary or can come from a specification

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What it Looks Like      Tennant      Roy      It Was Dark and Stormy      

 “I’m scared,” I said.

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Two Types of XML • Well-Formed • Valid

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Well-Formed XML • Follows general tagging rules: – All tags begin and end • But can be minimized if empty:
instead of



– All tags are lowercase – All tags are properly nested: • Mark Twain

– All attribute values are quoted: • <subject scheme=“LCSH”>Music

• Has identification & declaration tags • Software can make sure a document follows these rules 04:24 AM 04:24 AM

Valid XML • Uses only specific tags and rules as codified by one of: – A document type definition (DTD) – A schema definition

• Only the tags listed by the schema or DTD can be used • Software can take a DTD or schema and verify that a document adheres to the rules • Editing software can prevent an author from using anything except allowed tags 04:24 AM 04:24 AM

Ways to Use XML • Behind the scenes as a standard and easily transformed format for information • As a transfer syntax, to exchange information in a machine-parseable form • As a method of delivery direct to the user (not recommended) 04:24 AM 04:24 AM

Why is XML Important? • It is a standard, easily extensible way to encode loosely-structured as well as highlystructured information • Due to its easy parseability, software can transform it in countless ways, thereby allowing: – Easy migration paths – Alternative displays – On-the-fly response to user needs 04:24 AM 04:24 AM

XML vs. Databases (a simplistic formula)

• If your information is… – Tightly structured – Fixed field length – Massive numbers of individual items

• You need a database • If your information is… – Loosely structured – Variable field length – Massive record size

• You need XML 04:24 AM 04:24 AM

Serving XML to the Web • Directly in native form • Transformed to static HTML • Transformed to HTML dynamically

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Transforming XML: XSLT • XML Stylesheet Language — Transformations (XSLT) • A markup language and programming syntax for processing XML • Is most often used to: – Transform XML to HTML for delivery to standard web clients – Transform XML from one set of XML tags to another – Transform XML into another syntax/system 04:24 AM 04:24 AM

Required Components for Serving XML to the Web • An XML-encoded “document” • An XSLT stylesheet to… • …transform it to HTML or XHTML: – Static – Dynamic

• A CSS stylesheet (optional)

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XML Web Publishing Software • Required to: – Apply dynamic transformations to XML content – Render HTML dynamically for standard web browsers

• Just beginning to be available: – Cocoon: http://xml.apache.org/cocoon/ – AxKit: http://axkit.org/

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Case Study: Publishing Books @ the California Digital Library • Goals: – To create highly usable online versions of books – To create versions that will migrate easily as technology changes – To create an infrastructure that will support dynamic presentations of the same content 04:25 AM 04:25 AM

Case Study: Publishing Books @ the California Digital Library • Strategy:  Markup the texts in XML  Serve them dynamically using XML web publishing software (currently Cocoon)  Create different displays for different purposes, and a mechanism for allowing the user to select their preferred view  Find and apply an XML-aware search engine – Create a method by which users can create their own Adobe Acrobat versions

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AxKit mod_perl

Web Server

Cocoon Tomcat

Web Server

Cocoon Tomcat

Web Server I want this XML doc…

XSLT Stylesheet XML Doc

Cocoon Tomcat

Web Server

XSLT Stylesheet XML Doc

Cocoon Tomcat

Web Server

* Dynamic document

XHTML Document (no display markup)* HTML Stylesheet (CSS)

Transformation Information XML Doc

XSLT Stylesheet

Cocoon Tomcat

Web Server

* Dynamic document

Presentation XHTML Document (no display markup)* HTML Stylesheet (CSS)

Case Study: ILL ASAP ILL ASAP OCLC

Downloaded Requests

XML File

XSL Stylesheet

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Local Catalog

Internet Explorer

Printable XHTML File

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Service Tasmania Architecture

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Case Study: Univ. of Michigan

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Tips and Advice • Begin transitioning to XML now: – XHTML and CSS for web files, XML for static documents with long-term worth

• Do not rely on browser support of XML • DTDs? We don’t need no stinkin’ DTDs! • Get on the XML4Lib discussion list: http://sunsite.berkeley.edu/XML4Lib/ • Buy my book! 04:25 AM 04:25 AM

Resources • • • • •

Web sites Electronic discussions Books Magazines and journals Individuals

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