7 XML Web Site Architecture

 Example:

Apache Cocoon

, a Web publishing architecture based on XML technology http://xml.apache.org/cocoon – Apache: "XML publishing framework" » runs as a servlet (Java class under the control of a Web server, to handle incoming HTTP request) – Cocoon 1 (1999 –); not supported anymore – Cocoon 2 » more efficient (based on SAX instead of DOM) » better site administration (with "sitemaps") SDPL 2002 Notes 7: Apache Cocoon 1

Cocoon Philosophy (1/2)

 Separation of concerns with "pyramid of contracts": SDPL 2002 Notes 7: Apache Cocoon 2

Cocoon Philosophy (2/2)

 Different responsibilities <-> different groups – Site administrators, Developers, Content producers, Style designers – related declarations separated in different files – supports co-operation of specialised groups – enhances system modularity and extensibility – allows re-use of solutions to different tasks  Content, logic and style merged using XSL transformations SDPL 2002 Notes 7: Apache Cocoon 3

Example of typical use

  Automatic generation of HTML from (static or generated) XML documents – client-dependent processing possible, serving, e.g., » HTML to "typical" web browsers » WML to WAP-devices » XML to XML/XSL aware clients – also more sophisticated formatting (FOP -> PDF) In

Cocoon 1

processing of a request (by a sequence of

Processors

and a

Formatter

) controlled by embedded processing instructions (See next) SDPL 2002 Notes 7: Apache Cocoon 4

Example (of Cocoon

1

)

 Different views of content for different clients:

cocoon-process

type="xslt"?>

media="wap"

?> Welcome to XML! SDPL 2002 Notes 7: Apache Cocoon 5

Example (of Cocoon

1

)

  Cocoon 1 configured to handle various User Agents of the HTTP request – explorer, opera, lynx, netscape, java, wap Default style sheet welcome.xsl

specifies generation of HTML, and welcome-wml.xsl processing for WAP devices – See next SDPL 2002 Notes 7: Apache Cocoon 6

Stylesheet welcome-wml.xsl

type = "text/wml" … SDPL 2002 Notes 7: Apache Cocoon 7

Style sheet welcome-wml.xsl (2)

This page has been transformed from XML into WML by Cocoon's XSLT processor.

SDPL 2002 Notes 7: Apache Cocoon 8

Cocoon 2 Pipeline



Pipeline

: sequence of component interactions to process a request

– typical case: SDPL 2002 Notes 7: Apache Cocoon 9

Main Components of Cocoon 2 (1/2)



Generators

create XML as a SAX stream. E.g: – FileGenerator: XML file -> SAX stream – HTMLGenerator: HTML file -> XHTML (as SAX stream) – … (and more components can be added) 

Transformers

manipulate a SAX stream and pass the result to the next component – XSLT Transformer (default) – Include Transformers (for XML inclusion via URL) – SQL Transformer (to access a DB, and include results) – … SDPL 2002 Notes 7: Apache Cocoon 10

Components of Cocoon 2 (2)



Serializers

render a SAX stream to some result format (interpretable by the client) – HTML Serializer (default) – XML Serializer, Text Serializer – PDF/PS Serializer (based on FOP) – …  Components and pipelines declared in a Sitemap – In XML file sitemap.xmap

(translated to sitemap_xmap.java

) SDPL 2002 Notes 7: Apache Cocoon 11

Selecting a Pipeline

SDPL 2002 Notes 7: Apache Cocoon 12

Declaring Pipelines

… … SDPL 2002 Notes 7: Apache Cocoon 13

Setting up a pipeline

SDPL 2002 Notes 7: Apache Cocoon 14

XSP (Extensible Server Pages)

 Cocoon technology for dynamic content   Procedural code within static document content – similar with other server pages like JSP or ASP <

xsp:page

xmlns:xsp="

http://apache.org/xsp

language="java"> ...

" – XML document containing tag-based directives for generating dynamic content at request time – translated by XSP processor into Cocoon Generators SDPL 2002 Notes 7: Apache Cocoon 15

XSP: Embedding code into pages

 Example ( time.xsp

); Display the time of day:

language="java" xmlns:xsp="

http://www.apache.org/xsp

">

Date now = new Date();

It’s now //Variable for the time of day:

now

 XSP processor generates a Generator ...

SDPL 2002 Notes 7: Apache Cocoon 16

XSP page as Generator (fragments of)

public class time_xsp extends XSPGenerator { … //Variable for the time of day: Date now = new Date(); public void generate() throws SAXException { this.contentHandler.startDocument(); AttributesImpl attrs=new AttributesImpl(); attrs.addAttribute("", " title ", " title ", "CDATA", " Time of Day "); this.contentHandler.startElement("", " page ", " page ", attrs); … this.contentHandler.endDocument(); } SDPL 2002 Notes 7: Apache Cocoon 17

XSP to Generated Content to Result

SDPL 2002 Notes 7: Apache Cocoon 18

Example Result

 Final HTML page could be:

Time of Day

It's now Thu Dec 23 20:11:18 PST 1999

 OK, but can also separate logic from content (See next) SDPL 2002 Notes 7: Apache Cocoon 19

Library Tags

 Could replace the preceding with a

library tag:

...

It's now

...

 – Separation of concerns: »

programmers

encapsulate behaviour in dynamic tags »

content authors

use application-oriented markup to write XML documents Tag library: set of custom tags – for including code in documents – with its own namespace SDPL 2002 Notes 7: Apache Cocoon 20

Implementation of Tag Libraries

 Tag library implemented by a

logic sheet

– XSLT stylesheet translating XSP -> XSP – registered in configuration file cocoon.xconf

could be implemented by template <

xsp:expr

> formatDate(new Date(), " ");

xsp:expr

> SDPL 2002 Notes 7: Apache Cocoon 21

Using Tag Libraries

SDPL 2002 Notes 7: Apache Cocoon 22

Logic Sheets and Tag Libraries

  Separation of document structure and … – presentation:

stylesheets

give

presentation semantics

to tags – processing:

logic sheets

to tags give

procedural semantics Built-in tag libraries

for various dynamic information: – Request: request method & params, protocol, … – Session: methods for HTTP Session – ESQL: SQL database queries SDPL 2002 Notes 7: Apache Cocoon 23

ESQL: Example (1/2)

esql

="

http://apache.org/cocoon/SQL/v2

">

connectionName

SELECT name, addr FROM Emp

…

SDPL 2002 Notes 7: Apache Cocoon 24

ESQL: Example (2/2)

Sorry, no results!

SDPL 2002 Notes 7: Apache Cocoon 25

Cocoon used in practise?



April 2001:

– 57 Web sites powered by Cocoon 1 

April 2002:

– 34 Web sites powered by Cocoon 1 – 17 Web sites powered by Cocoon 2 » (34+17 < 57 !) – 9 service providers offering "Cocoon hosting" SDPL 2002 Notes 7: Apache Cocoon 26

Summary

 Apache Cocoon – "Publishing framework" based on XML technology » esp. on XSLT transformations – Configurable architecture » Components » Sitemap – XSP and tag libraries for dynamic content  Interesting and promising concept – Ideas may survive, perhaps in different systems » (E.g. IBM ServletManager?) SDPL 2002 Notes 7: Apache Cocoon 27