ITC570

ITC570 XML Programming Introduction to XML

Learning Objectives • Be able to: • Understand XML technologies and their roles. • Understand different components of an XML document. • Create a well-form XML document.

HTML and XML, I XML stands for eXtensible Markup Language HTML is used to mark up text so it can be displayed to users XML is used to mark up data so it can be processed by computers HTML describes both structure (e.g. , <h2>, ) and appearance (e.g. , , ) XML describes only content, or “meaning” In XML, you make up your own tags HTML uses a fixed, unchangeable set of tags 3

HTML and XML, II • HTML and XML look similar, because they are both SGML languages (SGML = Standard Generalized Markup Language) • Both HTML and XML use elements enclosed in tags (e.g. <body>This is an element</body>) • Both use tag attributes (e.g.,) • Both use entities(<,>,&,",') • More precisely, • HTML is defined in SGML • XML is a (very small) subset of SGML 4

HTML and XML, III • HTML is for humans • HTML describes web pages • You don’t want to see error messages about the web pages you visit • Browsers ignore and/or correct as many HTML errors as they can, so HTML is often sloppy • XML is for computers • XML describes data • The rules are strict and errors are not allowed • In this way, XML is like a programming language • Current versions of most browsers can display XML • However, browser support of XML is spotty at best 5

Example XML document <?xml version="1.0"?> <weatherReport> <date>7/14/97</date> <city>North Place</city>,<state>NX</state> <country>USA</country> High Temp: <highscale="F">103</high> Low Temp: <low scale="F">70</low> Morning: <morning>Partly cloudy, Hazy</morning> Afternoon: <afternoon>Sunny & hot</afternoon> Evening: <evening>Clear and Cooler</evening> </weatherReport> From: XML: A Primer, by Simon St. Laurent 6

Some technologies we may cover HTML XML Java HTML Forms servlets DTD XML Schemas JavaScript JSP Java SAX XHTML & CSS RELAX NG DOM Ajax JAXP Perl PHP Java Java JDBC But underneath... XSL SQL HTTP XSLT Apache XPath TCP/IP maybe RMI Tomcat CSS Sockets

Why XML? • Distributed applications need to share data. • plain text • structure and the meaning of the data are tightly defined. • Delivery of data to multi-devices • Separation of data and presentation.

bookshop book book title author price value initials surname XML Document – an Example <bookshop> <book> <title> Harry Potter and the Sorcerer’s Stone</title> <author> <initials>J.K</initials> <surname> Rowling</surname> </author> <price value=“$16.95”></price> </book> … </bookshop>

XML-related technologies DTD (Document Type Definition) and XML Schemas are used to define legal XML tags and their attributes for particular purposes CSS (Cascading Style Sheets) describe how to display HTML or XML in a browser XSLT (eXtensible Stylesheet Language Transformations) and XPath are used to translate from one form of XML to another DOM (Document Object Model), SAX (Simple API for XML, and JAXP (Java API for XML Processing) are all APIs for XML parsing 10

XML Parser • Required to read and manipulate XML documents. • Read the XML documents as a plain text and transform it into a data structure, typically tree, in the memory. • The applications, such as web browser, access the data structure and process the data according to their objectives. • Example: msxml

XML Document – Basic Components • Elements. • Attributes. • Character and Entity References. • Character Data (CDATA). • Processing Instruction. • Comments.

bookshop book book title author price value initials surname Elements Root Element (compulsory) Branch Elements attribute Leaf Element

Element • The basic building block of XML markups. • It may contains: • Text , Other elements (child elements) • Attributes, Character Data, Other markup, eg comments • Delimited with a start-tag and an end-tag. • Element can be empty. • The end-tag CANNOT be omitted as in HTML. • Each tag must consist a valid element type name.

Element’s Name • Element’s Name (Tag’s name) is CASE SENSITIVE. • <BOOK> <Book><book> • Trailing space is legal but will be ignored • <BOOK > = <BOOK>

Empty Element • Has no content. • May be associated with attribute. • Example: <img src=‘logo.png’></img> can be abbreviated into <img src=‘logo.png’/>

Attributes • Information regarding the element. “If elements are ‘nouns’ of XML then attributes are its ‘adjective’. • <tagname attribute_name=“attribute_value”>

Attributes vs Element • Determine by the semantic contents. • Attributes are characteristics of an element.

Character References • Use to display characters that are not supported by the input device (keyboard). • entering £ using US-ASCII keyboard. • Format: &#NNNNN; or &#xXXXX; • N decimal • X hexadecimal • Example: $ => $ OR &#x24

Entity References • Entities may be defined and used for: • Representing character used in mark-up • &lt == “<“ • &amp == “&” • String • &IR == Information Retrieval • Predefined entities: &lt, &gt, &quot, etc

Character Data • To escape blocks of text containing characters which would otherwise be recognized as markup. • <![CDATA[…]]> • <![CDATA[<greeting>Hello, world!</greeting>]]>

Character Data(2) <example> <![CDATA[&Warn;-&Disclaimer;<&copy 2001; &PM;>]]> </example> <example> &Warn;-&Disclaimer;<&copy 2001; &PM; &gt> </example>

Processing Instruction(PI) • Processing instructions (PIs) allow documents to contain instructions for applications. • <?target … instruction … ?> • Target is used to identify the application or other object to which the PI is directed. • <?xml-stylesheet href=“mystyle.css” type=“text/css”>

Comments • Syntax: <!–- comment text --> • Comments cannot be used within element tags. <tag>… some content … <tag <!– it is illegal-->> • Comments may never be nested. <!– Comments cannot <!– be nested --> like this -->

Names in XML • Names (as used for tags and attributes) must begin with a letter or underscore, and can consist of: • Letters, both Roman (English) and foreign • Digits, both Roman and foreign • . (dot) • - (hyphen) • _(underscore) • : (colon) should be used only for namespaces • Combining characters and extenders (not used in English) 30

Review of XML rules Start with <?xml version="1"?> XML is case sensitive You must have exactly one root element that encloses all the rest of the XML Every element must have a closing tag Elements must be properly nested Attribute values must be enclosed in double or single quotation marks There are only five pre declared entities 31

Another well-structured example • <novel> <foreword> <paragraph> This is the great American novel. </paragraph></foreword> <chapter number="1"> <paragraph>It was a dark and stormy night. </paragraph> <paragraph>Suddenly, a shot rang out! </paragraph> </chapter></novel> 32

XML as a tree novel foreword chapternumber="1" paragraph paragraph paragraph This is the greatAmerican novel. It was a darkand stormy night. Suddenly, a shotrang out! An XML document represents a hierarchy; a hierarchy is a tree 33

Valid XML • You can make up your own XML tags and attributes, but... • ...any program that uses the XML must know what to expect! • A DTD (Document Type Definition) defines what tags are legal and where they can occur in the XML • An XML document does not require a DTD • XML is well-structured if it follows the rules given earlier • In addition, XML is valid if it declares a DTD and conforms to that DTD • A DTD can be included in the XML, but is typically a separate document • Errors in XML documents will stop XML programs • Some alternatives to DTDs are XML Schemas and RELAX NG 34

Mixed content • An element may contain other elements, plain text, or both • An element containing only text:<name>David Matuszek</name> • An element (<name>) containing only elements:<name><first>David</first><last>Matuszek</last></name> • An element containing both:<class>CIT597 <time>10:30-12:00 MW</time></class> • An element that contains both text and other elements is said to have mixed content • Mixed content is legal, but bad • Mixed content makes it much harder to define valid XML • Mixed content is more complicated to use in a program • Mixed content adds no power to XML--it is never needed for anything 35

Example XML document, revised <?xml version="1.0"?> <weatherReport> <date>7/14/97</date> <place><city>North Place</city> <state>NX</state> <country>USA</country> </place> <temperatures><highscale="F">103</high> <low scale="F">70</low> </temperatures> <forecast><time>Morning</time> <predict>Partly cloudy, Hazy</predict> </forecast> <forecast><time>Afternoon</time> <predict>Sunny & hot</predict> </forecast> <forecast><time>Evening</time> <predict>Clear and Cooler</predict> </weatherReport> 36

Viewing XML • XML is designed to be processed by computer programs, not to be displayed to humans • Nevertheless, almost all current browsers can display XML documents • They don’t all display it the same way • They may not display it at all if it has errors • For best results, update your browsers to the newest available versions • Remember: HTML is designed to be viewed,XML is designed to be used 37

Structure of XML Document • XML document has to be well-formed. • Conform to syntax requirements • Conform to a simple container structure • Common structure of XML document: • Prolog • Body • Epilog

Prolog • Includes: • XML Declaration <?xml version=“1.0” encoding=‘utf-8’ standalone=“yes”> • Version is mandatory, encoding and standalone are optional • Document Type Declaration <!DOCTYPE • It is not DTD=Document Type Definition • A simple well-formed XML does not need it. • Schema declaration

Body & Epilog • Body • Contains 1 or more elements • The “contents” • Epilog • Hardly used • Can be used to identify end of document

Well-formed XML Document • Every element must have both a start tag and an end tag, e.g. <name> ... </name> • But empty elements can be abbreviated: <break />. • XML tags are case sensitive • XML tags may not begin with the letters xml, in any combination of cases • Elements must be properly nested, e.g. notbold and italic • Every XML document must have one and only one root element • The values of attributes must be enclosed in single or double quotes, e.g. <time unit="days"> • Character data cannot contain < or &

XML Process • An XML document is created in an editor. The XML parser reads the document and converts it into a tree of elements. • The parser passes the tree to the browser that displays it.

Summary • XML is a meta-markup language that enables the creation of markup languages for particular documents and domains. • XML documents are created in an editor, read by a parser, and displayed by a browser. • Be careful. XML isn’t completely finished. It will change and expand, and you will encounter bugs in current XML software.

ITC570

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