W3C XML XML Overview

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1 Overview Jaroslav Porubän 2008

2 References Tutorials, Specifications, World Wide Web Consortium, David Hunter, et al.: Beginning, 4th Edition, Wrox, 2007, 1080 p. ISBN Bill Evjen, et al.: Professional, Wrox, 2007, 856 p. ISBN Elliotte Rusty Harold, W. Scott Means: in a Nutshell, 3rd Edition, O'Reilly Media, 2004, 600 p. ISBN Erik Ray: Learning, 2nd Edition, O'Reilly Media, 2003, 432 p. ISBN

3 Document formats Binary format stream of bits + fast processing, effective storing of data + ability to store metadata proprietary formats, proprietary processing Text Format stream of characters + readable and writable by humans using standard text editors = universally interchangeable not standardized metadata and structuring ineffective storage and processing

4 What is? = extensible Markup Language is a technology concerned with the description and structuring of data document is platform (machine) independent form of storing data language is text-based document format with standardized metadata

5 A Brief History of Markup Standard Generalized Markup Language (SGML) attempt to combine a universally interchangeable data format with rich information storage capabilities SGML is a text-based language that can be used to mark up data SGML is a very complicated language HTML is based on SGML

6 Example <?xml version="1.0" encoding="windows-1250"?> <people> <person> <name license="kill"> <first>james</first> <last>bond</last> </name> </person> <person> <name> <first>major</first> <last>zeman</last> </name> </person> </people>

7 Example in Internet Explorer

8 Example in Mozilla Firefox

9 Why Extensible? Extensible we have full control over the creation of our document Anyone is free to mark up data in any way using the is not really a language, but a standard for creating languages that meet the criteria

10 Vocabulary Specific set of elements is called vocabulary Document type is a specific type of document, which must be structured in a specific way, to describe a specific type of information Standard vocabularies OpenDocument file format XHTML Scalable Vector Graphics (SVG) MathML

11 Viewpoints of Presentation Oriented Publishing (POP) Useful for Browsers and Editors Usually used for data that will be consumed by Humans Message Oriented Middleware (MOM) Useful for Machine-to-Machine data exchange Business-to-Business communication

12 Where Can Be Used Website Content Content oriented web sites Reducing Server Load Separated content and presentation Ajax Distributed Computing Messaging Web Services e-commerce Business-to-business, Business-to-consumer

13 Processor (Parser) A software module called an processor is used to read documents and provide access to their content and structure Parser is a program that reads input text and transforms it into a form suitable for further processing document can be read by any parser, regardless of what application was used to create it, or even what platform it was created on Standardized syntax of simplifies processing of documents

14 vs. HTML was designed to created to structure, store, and transport data HTML was designed to display data was designed to carry data, not to display data is not a replacement for HTML

15 vs. HTML separates data and presentation <name> <first>james</first> <last>bond</last> </name> HTML contains data tangled with presentation elements <html> <head><title>name</title></head> <body> <p>james Bond</p> </body> </html>

16 Components of describes the syntax that documents have to follow DTD, Schema defines the document types Namespaces provide a means to distinguish one vocabulary from another XPath querying language for addressing parts of an document XSL (XSLT + FO) style sheet and transformation language XQuery querying data directly from documents DOM document object model

17 Well-formed Documents Jaroslav Porubän 2008

18 Elements and tags Element is the main building block of Element is composed of start-tag, endtag and its content Tags constitute the markup of the document Element <country>slovakia</country> Start tag End tag

19 Hierarchies in <doc> <parent>this is some<em>text</em>in my element </parent> </doc>

20 Attributes Attributes are simple name/value pairs associated with an element Attached to the start-tag, but not to the end-tag <person> <name nickname="007"> <first>james</first> <last>bond</last> </name> </person>

21 Element or attributes? Elements and attributes can separate different types of information Elements can be more complex than attributes Attributes may use less space Attributes are unordered Attributes cannot contain multiple values Attributes cannot describe structures Attributes are normalized by processor

22 Example Only elements <note> <date> <day>21</day> <month>7</month> <year>2008</year> </date> <to>jane</to> <from>james</from> <heading>reminder</heading> <body>call me baby!</body> </note> Only attributes <note day="21" month="7" year="2008" to="jane" from="james" heading="reminder" body="call me baby!" />

23 Empty element Element with empty content <name nickname="007"></name> Option of writing this element using the special empty element syntax self-closing tag <name nickname="007" /> <name />

24 Comments Comments is a text that isn t really part of the document, but rather is intended for people who are reading the markup itself Comment starts with   Comment cannot be placed inside a tag <name  > It is not possible to use the double-dash string (--) inside a comment <! Illegal -- comment -->

25 Declarations Labels documents as being along with giving the parsers a few other pieces of information The declaration starts with the characters <?xml and ends with the characters?> A typical declaration <?xml version="1.0" encoding="utf-8"?>

26 Processing Instructions Sometimes it is needed to embed application-specific instructions into information to affect how it will be processed processing instructions The processing instructions starts with the characters <?processor and ends with the characters?> Example <?myproc PRINT "Hello"?>

27 Well-Formed documents must adhere to certain rules to be well-formed Rules make a universal format for interchanging data documents following all of the rules in the specification can be parsed by any parser

28 Rules for Well-formed Documents Spaces in tags must not follow < and / Attributes must have values enclosed in quotes Every start-tag must have a matching end-tag, or be a self-closing tag Tags can t overlap, elements must be properly nested documents can have only one root element Element names must obey naming conventions is case sensitive Illegal text content characters

29 Spaces in tags Wrong < first>james</first> <first>james< /first> <first>james</ first> <name/ > <name / > Correct <first >James</first> <first>james</first > <first >James</first> <name />

30 Attributes values Wrong <input checked> <input checked=true> <input checked="true'> <input checked="true" checked="true"> Correct <input checked='true'> <input checked="true"> <message text='quates "Message"'>

31 Every start-tag must have an endtag Wrong <p>first paragraph <p>second paragraph <hr> Correct <p>first paragraph</p> <p>second paragraph</p> <hr/>

32 Tags can t overlap Wrong <p>some <strong>formatted <em>text </strong>, but </em> no grammar no good! </p> Correct <p>some <strong>formatted <em>text</em> </strong> <em>, but </em> no grammar no good! </p>

33 Only one root element Wrong <person> James Bond </person> <person> Major Zeman </person> Correct <people> <person> James Bond </person> <person> Major Zeman </person> </people>

34 naming conventions Names can start with letters or the underline "_" After the first character, numbers, hyphens "-", and periods "." are allowed Names can t contain spaces Names can t contain the colon ":" character Names can t start with the letters xml, in uppercase, lowercase, or mixed Wrong <xml-tag> <123> <fun=xml> <my tag>

35 is case sensitive Tags in are case sensitive Wrong <first>james</first> <FIRST>James</First> <p>paragraph</p> Correct <first_name>james</first_name> <first-name>james</first-name> <firstname>james</firstname> <FirstName>James</FirstName>

36 Illegal text content characters Characters < or & cannot be directly written in text content Escaping characters - Entities Character & < > ' " Entity References & < > ' " CDATA not parsed, PCDATA parsed <exp><![cdata[x < 10 & y < 20]]></exp>

37 HTML is not an Some pair elements have not required endtag <p>this is paragraph Unpaired elements are not self enclosed tags <br> Attributes can exists without values <textarea readonly> Attribute value may be written without quotes <td colspan=3> Tags can overlap <p><a href="a.html">text</p></a>

38 XHTML is an There are no optional end-tags <p>this is paragraph</p> Unpaired elements are self enclosed tags <br /> Attributes must have values <textarea readonly="readonly"> Attribute value must be written with quotes <td colspan="3"> Tags cannot overlap <p><a href="a.html">text</a></p> Presentation is separated in stylesheets (css)

Introduction to XML. An Example XML Document. The following is a very simple XML document.

Introduction to XML. An Example XML Document. The following is a very simple XML document. Introduction to XML Extensible Markup Language (XML) was standardized in 1998 after 2 years of work. However, it developed out of SGML (Standard Generalized Markup Language), a product of the 1970s and