1	The Document Object Model (DOM) And its Role for Application Development
2	Overview The need for a Document Object Model Brief explanation of the DOM model DOM and the system architecture Pros and Cons of the DOM model Decision Criteria
3	Application Development Broad view Product definition Specifications … Implementation Product Life Cycle Narrow view Application Implementation Software Engineering Part Source Code Generation Product Definition Product Requirements Application Specification System Design System Architecture System Definition Functional Specification Implementation Maintenance
4	Justifying Document Model Standards Pre SGML era WinWord, RTF, AmiPro, MIF, Ventura Publisher, … Hard to reuse for developers Converter writing was/is an “art” – lack of documentation, proprietary interfaces SGML/XML era: (X)HTML, DHTML, XML Support for scripting languages in dynamic web pages Document generation / production / publishing XML standards Science - Math XML, Astronomy … Publishing, technical documentation, DocBook Translation Data centric vs document centric XML Information exchange/control in and between applications Application control through ini/properties File Internet – http - enabled applications XML-RPC WebDAV SOAP, UDDI, OWL, WSDL, RDF … Tomcat - servlets
5	Restricting … What is DOM? Acronym: “Document Object Model” „The Document Object Model is a platform- and language-neutral interface that will allow programs and scripts to dynamically access and update the content, structure and style of documents. ...“ The Document Object Model (DOM) is an application programming interface (API) for valid HTML and well-formed XML documents. It defines the logical structure of documents and the way a document is accessed and manipulated. W3C - http://www.w3.org/DOM/ Initially as tool for modeling for DHTML in browsers Several Levels 1 – 3 Current Working Draft: DOM Level 3
6	What does DOM provide? The DOM kernel is a set of APIs (definitions) Not an implementation Defined using IDL (OMG) Different programming languages need to realize those API definitions Provides an object-based interface Tree based In contrast to an event-based ones like SAX (Simple API for XML) DOM interface is specified in several modules Core, XML, HTML … Suppliers may support only some modules This is important when choosing a specific implementation!
7	DOM Levels 1-3
8	DOM Model Implementation Represents the XML document as a tree based data structure One step parsing Whole XML document is kept in main memory Allows “(randomly) accessing/manipulating” of XML documents In contrast to other models like SAX Parser realizes the DOM model for applications
9	Application examples using DOM Editors Tools which edit XML documents Web Browsers IE, Netscape … Publishing Tools Internet enabled applications WebDAV, SOAP Servlet Engines Tomcat … Configuration Management Eclipse GUI Building GNOME project
10	XML Application Integration XML logic is part of the application logic
11	DOM and Application Integration XML logic is separated using a DOM parser and API methods from the application logic
12	Pros and Cons Standard No need to write own parser and complex data structures to hold the xml data Easy to implement Several alternative implementations available for different programming languages Immediate access to different parts of the document Read / write support Memory Usage High “deferred DOM” Computational efficiency Low Persistence needs to be handled manually Use of db’s like eXist, Xindice, Tamino Level 3 ?
13	Decision Criteria - XML Dealing mainly with document or data centric XML objects? Address book, databases vs. technical documentation, articles, books Ideal for document centric applications Browsers, editors Document size; > 10 MB?? Complex DTD / XML data? For simple restricted data centric XML use SAX, JDOM, regular expressions … Mixed content support Support of XML Schema required?
14	Decision Criteria – Access Functionality Direct access to the various document parts needed? Choose DOM Random access to all document elements For sequential access SAX is more efficient Manipulating XML document? Use DOM Supports creating / changing content
15	Decision Criteria – Document Size Intended document size supported? May require tests Dependency on main memory available Server / client architecture? “deferred DOM” PDOM as a commercial alternative (Infonyte) Necessity to handle huge documents or several documents at a time? May require a lot of memory if several documents are loaded at the same time Example: Diff’s between several documents
16	Decision Criteria – Persistence How is the DOM object serialized? Approaches DOM Level 3 Simple file DB APIs XML databases Xindice eXist Tamino Relational databases …
17	Decision Criteria - Language Support Availability for several programming languages Strength of DOM Xerces: Java, C++, Perl Java Script Through browsers – mostly built-in Java Many Open Source projects C++, C Perl Visual Basic …
18	Decision Criteria – Implementation Phase DOM is popular for scripting languages JavaScript, web sites built-in Performance DOM is not as memory / time efficient as SAX
19	Decision Criteria – DOM Level Support Which parser is used? Which level and modules are supported by a specific parser?
20	Summary: Why to use the DOM Model Intuitive (tree based) standard model for document centric applications Object oriented representation Makes writing re-usable / multi-usable documents for application writing a reality Simple way to access XML document structures Writing own parsers is complex Basic document model and access functions Based on a Component Approach Simply exchange the DOM parsers Internet enabled applications Implicitly in Greatly simplifies writing XML based applications