Unit 9 Notes

"An Introduction to the Extensible Markup Language (XML)"

I tried to focus on what XML is and is not - in hope to distinguish it from other things that we are learning about dealing with computer language...

• XML is a subset of the SGML which is designed to maker it easier to interchange structured documents over the Internet
• Unlike SGML, XML does not require the presence of a DTD which means that XML system can assign a default definition for undeclared components of a markup
• XML was not designed to be a standardized way of coding text - instead, it is a formal language that can be used to pass info of component parts of a doc to other computer systems.
• XML differs from other markup languages because it sets out to clearly identify the boundaries of every part of a doc
• XML-coded files are ideal for storing in databases because they are object-orientated and hierarchical in nature - meaning that they can adopt to any type of database = ensure transferability to a many types of hardware and software environments
  

"Extending Your Markup: An XML Tutorial"

For some reason I did not find this article as helpful as the above article, and actually... it made me more confused about XML after reading this, than I was after reading the previous article...

• XML = semantic language that lets you meaningfully annotate text
• XML syntax starts with a prolog and contains one element
• Elements can be either nonterminal or terminal
• Elements have 0 or more attributes and attributes can have different data types
• There are XML extensions which include namespaces which allow more powerful addressing and linking abilities
• DDML, DCD, SOX, and DCD, address several disadvantages with XML documents
• Developments to watch = RDF (resource description framework) and DOM (document object model)

"Survey of XML Standards: Part 1"

I found this article very confusing - because XML was suppose to be something simple... but with all these "technologies" which seem so alike... I'm not convinced that this is so.

• XML - vast and growing with a huge variety of standards and technologies that interact in complex ways
• Outlines the most important XML technologies - all are standard
• XML 1.0 to XML 1.1 which is the first revision of XML that changes the definition of a well-formed XML document (doc or docs)
  
• XML 1.1 also revises the treatment of characters and adds to the list of line-end

• XML Namespaces (also brought up in "Extending your Markup") which is a mechanism for universal naming of elements and attributes in XML docs
• XML Base - means of associating XML elements with URIs in order to specify how relative URIs are resolved in relevant XML processing actions
• XInclude (XML Inclusion) provides a system for merging XML docs
• XML InfoSet (Information Set) defines an abstract way of describing an XML doc as information sets, with specialized properties
• Canonical XML - generates a physical representation of an XML doc that accounts for the variations allowed in XML syntax without changing the meaning
• XPath (XML Path Language) is a syntax and a data model for addressing parts of an XML doc and is also the most successful XML technology (beside the XML 1.0)
• XPointer (X Pointer Framework) defines a language that can be used to refer to fragments of an XML doc
• XLink (XML Linking Language) provides a generic framework for expressing links in XML docs and allows much richer linking than one-way HTML
• Relax NG - an XML schema langage that can be used to define a limit XML vocabularies
• W3C XML Schema defines (yet another) schema language for XML. One part allows to constrain the structure of the document and the second part allows to constrain the contents of a simple element and attributes
• Schematron - Schema language that uses a different approach than DTD, Relax NG, or WXS. You register a collection of rules against which the XML doc is to be checked, rather than mapping out the entire tree structure of the XML format you are trying to express from root node to the leaves.

"XML Schema Tutorial"

Again, probably the most helpful article out of them all again. I really like the way this website approaches tutoring those who have no idea what they are doing with languages. It says all the basic stuff that the first two articles said, but also gives better explanations and just seems to display better what they are talking about.

Muddiest Point: How can XML system assign a default definition for undeclared components of the markup but SGML cannot (wouldn't they just create a fix for that in SGML?)