XML technologies : Overview of the course

Jean-François Perrot

1. Trees are everywhere in computers
2. XML is about trees
3. The success of XML is based on
4. The present course

1. Trees are everywhere in computers

   • Trees live in central memory (as objects, with a heavy use of pointers).
     
     
   • In order to exchange trees over the Internet we need a file-based (text) representation
     also called serialization.
     (For instance, program texts, using the concrete syntax of a programming language, are nothing more than
     file-based representations of Abstract Syntax Trees - ASTs)
     
     
   • XML is
     
     1. a uniform solution to the problem of representing trees as text files;
        
     2. an Object-Oriented framework tfor representing trees as objects (i.e. the Document Object Model - DOM).
        
     
     Note that other popular solutions for the same problem exist, like JSON or YAML.
     
   
   

2. XML is about trees

   1. Parsing

      1. Principle : converting a tree given as a text (from a file or from the Net)
         into an object of some programming language (Java, PHP, C++,...), which is then processed by an ordinary program.
         
         
      2. If the chosen format for the generated object is DOM, then parsing is fully automated.
         

   2. Specifying tree structure (Validation)
      

      Any treament of a tree will be based on knowledge about the structure of that tree.
      If the given tree fails to conform with the expected structure, the treatment results in error (syntax error...).
      A way to reduce such errors is to check beforehand that the tree is syntactically correct,
      
      • not only as XML,
        
      • but also as regards the intended treatment (then the tree is said to be valid).
        
      
      Trees with the "same" structure build XML dialects - or XML-based languages.
      Each language has its own use (semantics) provided by standard software - see below.
      

   3. Transforming trees
      

      (from one XML-based language to another).
      Transforming an (unusable) source document into a usable one.
      

3. The success of XML is based on

   • A world-wide consensus about technical details (W3C).
     
     
   • A fast-growing number of XML-based languages (dialects) : e.g. XHTML, SVG...
     
     
     • So much so that some people define XML as

       a metalanguage to design markup languages, i.e. text language where semantic and structure are added to the content
       using extra "markup" information enclosed between angle brackets.
       HTML is the most well-known markup language.
       [libxml]

     • Some of those XML-dialects are dedicated to XML technology itself (e.g. XSLTransform, XMLSchema)
       
       
     • Almost all configuration files are now styled in XML instead of ad-hoc syntaxes (e.g. make...)
       
       
   • A massive set of tools
     
     • for XML in general
       
       • generic libraries such as libxml2 (originally in C, but with a number of "bindings" for other languages)
         
       • XML frameworks in virtually every programming language (e.g. Java : JAXP, JAXB)
         
         
     • for various XML languages e.g.
       
       • Web browsers for XHTML, SVG and others
         
       • Apache-FOP for the XSL-FO dialect,
   
   

4. The present course

   1. Five sessions

      + a final project (base for evaluation)
      
      
      1. XML syntax & XML namespaces
      2. Validation (XML Schemas and  RNG Grammars)
      3. XPath
      4. Transforms-1
      5. Transforms-2
      6. Project
      
      Basic toolkit : Eclipse XML perspective
      

   2. Project theme

      The report on the Java project written in DocBook
      
      
      • DocBook is an XML language for writing printable documents (books or papers) as trees
        (as a sequence of chapters, each cuapter containing title, paragraphs etc)
        [Wikipedia]
        
        
      • Various tools are available to transform DocBook into readable format (e.g. XHTML, pdf via XSL-FO)
        
        
      • Example : Course notes on DocBook written in DocBook
        
        1. the XML-DocBook file
        2. the XHTML rendering
        3. the pdf version.
           
           
        Note that the pdf was produced from an XML file (in XSL-FO language) by means of the Apache-FOP program,
        in the same way as the screen display is produced by the browser from the XML (in XHTML language) source code.