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7 XML Web Site Architecture

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)

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7 XML Web Site Architecture

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  1. 7 XML Web Site Architecture • Example: Apache Cocoon, a Web publishing architecture based on XML technologyhttp://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") Notes 7: Apache Cocoon

  2. Cocoon Philosophy (1/2) • Separation of concerns with "pyramid of contracts": Notes 7: Apache Cocoon

  3. 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 Notes 7: Apache Cocoon

  4. 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) Notes 7: Apache Cocoon

  5. Example (of Cocoon 1) • Different views of content for different clients: <?xml version = "1.0"?> <!-- Fig. 16.1 in Deitel et al. --> <!-- Pass document through an XSLT processor: --> <?cocoon-process type="xslt"?> <?xml-stylesheet href="welcome.xsl" type="text/xsl"?> <!-- default view --> <?xml-stylesheet href = "welcome-wml.xsl" type="text/xsl" media="wap"?> <!-- wap-view --> <myMessage> <message>Welcome to XML!</message> </myMessage> Notes 7: Apache Cocoon

  6. 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 Notes 7: Apache Cocoon

  7. Stylesheet welcome-wml.xsl <!-- Fig. 16.4 in Deitel et al. --> <xsl:stylesheet version = "1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match = "myMessage"> <!-- Add a Cocoon instruction to format the result as WML: --> <xsl:processing-instruction name = "cocoon-format">type = "text/wml" </xsl:processing-instruction> … Notes 7: Apache Cocoon

  8. Style sheet welcome-wml.xsl (2) <wml><card> <p><xsl:value-of select="message"/></p> <p>This page has been transformed from XML into WML by Cocoon's XSLT processor. </p> </card> </wml> </xsl:template> <!-- for 'myMessage' --> </xsl:stylesheet> Notes 7: Apache Cocoon

  9. Cocoon 2 Pipeline • Pipeline: sequence of component interactions to process a request • typical case: Notes 7: Apache Cocoon

  10. 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) • … Notes 7: Apache Cocoon

  11. 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) Notes 7: Apache Cocoon

  12. Selecting a Pipeline Notes 7: Apache Cocoon

  13. Declaring Pipelines <!-- Fragment of sitemap.xmap: --> <map:sitemap xmlns:map="http://apache.org/cocoon/sitemap/1.0"><map:components> … </map:components> <!-- Select pipeline based on request URI: --> <map:match pattern="hello.html"> <map:generate src="docs/hello-page.xml" /> <map:transform src="style/simpl2html.xsl"/> <map:serialize type="html" /> </map:match> … </map:sitemap> Notes 7: Apache Cocoon

  14. Setting up a pipeline Notes 7: Apache Cocoon

  15. 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 Notes 7: Apache Cocoon

  16. XSP: Embedding code into pages • Example (time.xsp); Display the time of day: <xsp:page language="java" xmlns:xsp="http://www.apache.org/xsp"> <xsp:logic>//Variable for the time of day: Date now = new Date(); </xsp:logic> <!-- root of resulting document: --> <page title="Time of Day"> <p>It’s now<xsp:expr>now</xsp:expr></p> </page> </xsp:page> • XSP processor generates a Generator ... Notes 7: Apache Cocoon

  17. 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(); } Notes 7: Apache Cocoon

  18. XSP to Generated Content to Result Notes 7: Apache Cocoon

  19. Example Result • Final HTML page could be: <html> <head><title>Time of Day</title></head> <body> <h3 style="color: navy; text-align: center">Time of Day</h3> <p>It's now Thu Dec 23 20:11:18 PST 1999</p> </body> </html> • OK, but can also separate logic from content (See next) Notes 7: Apache Cocoon

  20. Library Tags • Could replace the preceding with a library tag: ...<p>It's now <util:date format="…"/></p> ... • 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 Notes 7: Apache Cocoon

  21. Implementation of Tag Libraries • Tag library implemented by a logic sheet • XSLT stylesheet translating XSP -> XSP • registered in configuration file cocoon.xconf <util:date format="yy/MM/dd hh:mm:ss aa" /> could be implemented by template <xsl:template match="util:date" > <xsp:expr> formatDate(new Date(), "<xsl:value-of select='@format' />"); </xsp:expr> </xsl:template> Notes 7: Apache Cocoon

  22. Using Tag Libraries Notes 7: Apache Cocoon

  23. Logic Sheets and Tag Libraries • Separation of document structure and … • presentation: stylesheets give presentation semantics to tags • processing: logic sheets give procedural semantics to tags • Built-in tag libraries for various dynamic information: • Request: request method & params, protocol, … • Session: methods for HTTP Session • ESQL: SQL database queries Notes 7: Apache Cocoon

  24. ESQL: Example (1/2) <?xml version="1.0" ?> <xsp:page language="java" xmlns:xsp="http://www.apache.org/xsp" xmlns:esql="http://apache.org/cocoon/SQL/v2"> <esql:connection> <esql:pool>connectionName</esql:pool> <esql:execute-query> <esql:query> SELECT name, addr FROM Emp </esql:query> … Notes 7: Apache Cocoon

  25. ESQL: Example (2/2) <esql:results> <table><esql:row-results> <tr><td><esql:get-string column="name"/></td> <td><esql:get-string column="addr"/></td> </tr></esql:row-results> </table> </esql:results> <esql:no-results> <p>Sorry, no results!</p> </esql:no-results> </esql:execute-query> </esql:connection> </xsp:page> Notes 7: Apache Cocoon

  26. 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" Notes 7: Apache Cocoon

  27. 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?) Notes 7: Apache Cocoon

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