Intro to xml


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Intro to xml

  1. 1. ObjectivesObjectives History andMarkup languages Comparison between XML and HTML XML Syntax XML Design rationale XML Elements and Attribute XML DTD XML Validation
  2. 2. HistoryHistory SGML HTML XML 1985 1990 1995/98 Standardized General Markup Language HyperText Markup Language eXtensible Markup Language
  3. 3. Introduction of XML  XML stands for EXTENSIBLE MARKUP LANGUAGE.  XML represent the text information in a standard format .  XML was designed to transport and store information.  It is used for documents containing structure information in a reliable way.
  4. 4. What do mark up languages do? 􀂄 Markup languages consist of a set of markup conventions used for encoding texts. 􀂄 A markup language specifies – 􀂄 What markup is allowed 􀂄 What markup is required 􀂄 How the mark up is distinguished from text 􀂄 What the markup means
  5. 5. Features of XML • XML files are text files, which can be managed by any text editor. • XML is very simple, because it has less than 10 syntax rules. • XML tags are not predefined. You must define your own tags • XML is designed to be self-descriptive
  6. 6. ADVANTAGES OF XML  It can represent common computer science data structures: records, lists and trees.  Its self-documenting format describes structure and field names as well as specific values.  The strict syntax and parsing requirements make the necessary parsing algorithms extremely simple, efficient, and consistent  XML is heavily used as a format for document storage and processing, both online and offline.
  7. 7. How is XML different from HTML?  HTML and XML have different sets of goals. HTML was designed to display data and hence focused on the ‘look’ of the data, XML was designed to describe and carry data and hence focuses on ‘what data is’.  XML Does Not DO Anything  HTML and XML are complementary to each other.
  8. 8. XML Syntax Rules  Now lets take a look at some of the important rules of XML syntax.  All XML Elements Must Have a Closing Tag  XML Tags are Case Sensitive <p>This is a paragraph.</p> <br /> . The tag <Letter> is different from the tag <letter>.
  9. 9. XML Syntax Rules XML Elements Must be Properly Nested XML Documents Must Have a Root Element <b><i>This text is bold and italic</i></b> <root> <child> <subchild>.....</subchild> </child> </root>
  10. 10. XML Elements  An Element is a technical term for a textual unit, viewed as a structural component.  Different types of elements are given different names  The names do not express meaning and meanings are application dependent  XML elements are extensible
  11. 11. Authoring XML Elements An XML element is made up of a start tag, an end tag, and data in between. Example: <director> Matthew Dunn </director> Example of another element with the same value: <actor> Matthew Dunn </actor> XML tags are case-sensitive: <CITY> <City> <city>
  12. 12. Authoring XML Attribute (cont’d) An attribute is a name-value pair separated by an equal sign (=). Example: <City ZIP=“94608”> Emeryville </City> Attributes are used to attach additional, secondary information to an element.
  13. 13. XML Attributes 􀂄 XML elements can have attributes in name/value pairs as in HTML. 􀂄 Attributes must always be in quotes. Either single or double quotes are valid, though double quotes are most common. 􀂄 Attributes are always contained within the start tag of an element.
  14. 14. What is an XML DTD ? 􀂄 DTD stands for Document Type Definition. 􀂄 DTD is a formal model for defining the role of each element 􀂄 It formally defines the relationship between the various elements that form the documents. 􀂄 The purpose of a Document Type Definition is to define the legal building blocks of an XML document.
  15. 15. Document Type Definitions (DTDs 1)Document Type Definitions (DTDs 1) XML document types can be specified using a DTD DTD does not constrain data types All values represented as strings in XML DTD definition syntax <!ELEMENT element (subelements-specification) > <!ATTLIST element (attributes) > … more details later Valid XML documents refer to a DTD (or other Schema)
  16. 16. Document Type Definitions (DTDs 2)Document Type Definitions (DTDs 2) <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE test PUBLIC "-//Webster//DTD test V1.0//EN" <test> "test" is a document element </test> <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE test PUBLIC "-//Webster//DTD test V1.0//EN" <test> "test" is a document element </test> <!DOCTYPE test [ <!ELEMENT test EMPTY> ]> <test/> <!DOCTYPE test [ <!ELEMENT test EMPTY> ]> <test/> External Public DTD Declaration Internal DTD Declaration <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE test SYSTEM "test.dtd"> <test> "test" is a document element </test> <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE test SYSTEM "test.dtd"> <test> "test" is a document element </test> External DTD Declaration referring to a file or a URL test = name of the root element DTD is defined in file test.dtd DTD is defined inside XML Application should know DTD
  17. 17. XML Validation  There are two types of XML documents  “Well formed” XML  An XML document that conforms to the syntax of XML is called ‘well formed’  “Valid” XML  An XML document that conforms to a DTD  Is called a ‘Valid’ DTD
  18. 18. What is a well-formed XML document ?What is a well-formed XML document ? Well-formed documents follow basic syntax rules e.g. there is an XML declaration in the first line there is a single document root all tags use proper delimiters all elements have start and end tags But can be minimized if empty: <br/> instead of <br></br> all elements are properly nested <author> <firstname>Mark</firstname> <lastname>Twain</lastname> </author> appropriate use of special characters
  19. 19. XML Validator Use our XML validator to syntax-check your XML. XML Errors Will Stop You Syntax-Check Your XML Syntax-Check an XML File Validate Your XML Against a DTD
  20. 20. Viewing XML Files Raw XML files can be viewed in all major browsers. Don't expect XML files to be displayed as HTML pages. Viewing XML Files Viewing an Invalid XML File Look at this XML file: note.xml Look at this XML file: note_error.xml
  21. 21. XML applications 􀂄 B2B 􀂄 EDI 􀂄 Journal publishing 􀂄 Database development
  22. 22. XML future Given the direction in which it is growing and the level of support that XML has received the XML appears to be the future of Web publishing
  23. 23. SummarSummarYY XML has a wide range of applications XML is just a formalism (meta-language), unlike HTML The W3C framework includes General purpose (accessory, transducing, ..) languages such as XML Schema, XSLT, XPath, XQuery, Xlink, RDF, … Useful languages for contents (vector graphics, multimedia animation, formulas Other organizations Define domain-specific vocabularies Define alternative XML-based general purpose languages XML is mostly used “behind the scene”, but increasingly directly for web contents (via XSLT mostly)