xml 6 6.1 xml. outline 1. xml 2. xsl / xslt 3. dtd 4. dom 5. xsd 6. xpath 7. xforms
TRANSCRIPT
XML
6
6.1 XML
Outline
1. XML
2. XSL / XSLT
3. DTD
4. DOM
5. XSD
6. XPath
7. XForms
What is XML?
XML stands for EXtensible Markup Language
A meta-language for descriptive markup: you invent your own tags
XML uses a Document Type Definition (DTD) or an XML Schema to describe the data XML with a DTD or XML Schema is designed to be self-descriptive
Built-in internationalization via Unicode
Built-in error-handling
Optimized for network operations
Tons of support from the big IT companies
Some History
SGML (Standard Generalized Markup Language) ISO Standard, 1986, for data storage & exchange Metalanguage for defining languages (through DTDs) A famous SGML language: HTML Separation of content and display Used in U.S. gvt. & contractors, large manufacturing
companies, technical info. Publishers,... SGML reference is 600 pages long
XML W3C recommendation in 1998 Simple subset (80/20 rule) of SGML: “ASCII of the Web”,
“Semantic Web” XML specification is 26 pages long
Timeline
1986 SGML becomes a standard
1989 Tim Berners-Lee creates the WWW
1994 W3C established
1998 XML 1.0 W3C Recommendation
Jan 2000 XHTML becomes W3C Recommendation A Reformulation of HTML 4 in XML 1.0
Oct 2000 W3c XML 1.0 (Second Edition) Recommendation http://www.w3.org/TR/REC-xml
Oct 2002 XML 1.1 Candidate Recommendation updates XML to use Unicode 3
XML and HTML
XML is not a replacement for HTML
XML was designed to carry data
XML and HTML were designed with different goals XML was designed to describe data and to focus on
what data is HTML was designed to display data and to focus on
how data looks.
HTML is about displaying information, while XML is about describing information
HTML and XML, I
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. <p>, <h2>, <em>) and appearance (e.g. <br>, <font>, <i>)
XML describes only content, or “meaning”
HTML uses a fixed, unchangeable set of tags
In XML, you make up your own tags
HTML and XML, II
HTML and XML look similar, because they are both SGML languages Both HTML and XML use elements enclosed in tags Both use tag attributes
More precisely, HTML is defined in SGML XML is a (very small) subset of SGML
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
XML does not DO anything
XML was not designed to DO anything
XML is created to structure, store and to send information
The following example is a book info, stored as XML:
<?xml version='1.0'?><bookstore> <book genre=‘autobiography’ publicationdate=‘1981’ ISBN=‘1-861003-11-0’> <title>The Autobiography of Benjamin Franklin</title> <author> <first-name>Benjamin</first-name> <last-name>Franklin</last-name> </author> <price>8.99</price> </book> …</bookstore>
XML is Free and Extensible
XML tags are not predefined You must "invent" your own tags The tags used to mark up HTML documents and the
structure of HTML documents are predefined The author of HTML documents can only use tags
that are defined in the HTML standard
XML allows the author to define his own tags and his own document structure
XML Future
XML is going to be everywhere
XML is a cross-platform, software and hardware independent tool for transmitting information.
DocumentsConfiguration
Database
Application X
Repository
XML XML
XML XML
Benefits of XML
Open W3C standard
Representation of data across heterogeneous environments Cross platform Allows for high degree of interoperability
Strict rules Syntax Structure Case sensitive
How can XML be Used?
XML can Separate Data from HTML
With XML, your data is stored outside your HTML
XML is used to Exchange Data
With XML, data can be exchanged between incompatible systems
With XML, financial information can be exchanged over the Internet
XML can be used to Share Data
XML can be used to Store Data
XML can make your Data more Useful
XML can be used to Create new Languages
Components of an XML Document
Elements Each element has a beginning and ending tag
<TAG_NAME>...</TAG_NAME> Elements can be empty (<TAG_NAME />)
Attributes Describes an element; e.g. data type, data range, etc. Can only appear on beginning tag
Processing instructions Encoding specification (Unicode by default) Namespace declaration Schema declaration
Components of an XML Document
Processing Instructions
Elements
Elements with Attributes
<?xml version=“1.0” ?>
<?xml-stylesheet type="text/xsl" href=“template.xsl"?>
<ROOT>
<ELEMENT1><SUBELEMENT1 /><SUBELEMENT2 /></ELEMENT1>
<ELEMENT2> </ELEMENT2>
<ELEMENT3 type=‘string’> </ELEMENT3>
<ELEMENT4 type=‘integer’ value=‘9.3’> </ELEMENT4>
</ROOT>
XML declaration
The XML declaration looks like this:<?xml version="1.0" encoding="UTF-8" standalone="yes"?> The XML declaration is not required by browsers, but is
required by most XML processors (so include it!) If present, the XML declaration must be first--not even
whitespace should precede it Note that the brackets are <? and ?> version="1.0" is required (this is the only version so far) encoding can be "UTF-8" (ASCII) or "UTF-16" (Unicode), or
something else, or it can be omitted standalone tells whether there is a separate DTD
Processing Instructions
PIs (Processing Instructions) may occur anywhere in the XML document (but usually first)
A PI is a command to the program processing the XML document to handle it in a certain way
XML documents are typically processed by more than one program
Programs that do not recognize a given PI should just ignore it
General format of a PI: <?target instructions?>
Example: <?xml-stylesheet type="text/css" href="mySheet.css"?>
XML Elements
An XML element is everything from the element's start tag to the element's end tag
XML Elements are extensible and they have relationships
XML Elements have simple naming rules Names can contain letters, numbers, and other characters Names must not start with a number or punctuation character Names must not start with the letters xml (or XML or Xml ..) Names cannot contain spaces
XML Attributes
XML elements can have attributes
Data can be stored in child elements or in attributes
Should you avoid using attributes? Here are some of the problems using attributes:
attributes cannot contain multiple values (child elements can) attributes are not easily expandable (for future changes) attributes cannot describe structures (child elements can) attributes are more difficult to manipulate by program code attribute values are not easy to test against a Document Type
Definition (DTD) - which is used to define the legal elements of an XML document
An XML Document
<?xml version='1.0'?><bookstore> <book genre=‘autobiography’ publicationdate=‘1981’ ISBN=‘1-861003-11-0’> <title>The Autobiography of Benjamin Franklin</title> <author> <first-name>Benjamin</first-name> <last-name>Franklin</last-name> </author> <price>8.99</price> </book> <book genre=‘novel’ publicationdate=‘1967’ ISBN=‘0-201-63361-2’> <title>The Confidence Man</title> <author> <first-name>Herman</first-name> <last-name>Melville</last-name> </author> <price>11.99</price> </book></bookstore>
Another XML Document
<?xml version="1.0"?><weatherReport> <date>7/14/97</date> <city>North Place</city>, <state>NX</state> <country>USA</country> High Temp: <high scale="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>
XML Validation
XML with correct syntax is Well Formed XML
XML validated against a DTD is Valid XML
Rules For Well-Formed XML
There must be one, and only one, root element
All XML elements must have a closing tag
Sub-elements must be properly nested A tag must end within the tag in which it was started
Attributes are optional Defined by an optional schema
Attribute values must be enclosed in “” or ‘’
Processing instructions are optional
XML is case-sensitive <tag> and <TAG> are not the same type of element
White space is preserved
CR / LF is converted to LF
Comment in XML is similar to that of HTML
XML DTD
A DTD defines the legal elements of an XML document defines the document structure with a list of legal
elements
XML Schema XML Schema is an XML based alternative to DTD
Errors in XML documents will stop the XML program
XML Validators
Browsers Support for XML
Netscape 6 supports XML
Internet Explorer 5.0 supports the XML 1.0 standard
Internet Explorer 5.0 has the following XML support: Viewing of XML documents Full support for W3C DTD standards XML embedded in HTML as Data Islands Binding XML data to HTML elements Transforming and displaying XML with XSL Displaying XML with CSS Access to the XML DOM
Viewing XML Files
Raw XML files can be viewed in IE 5.0 (and higher) and in Netscape 6 but to make it display like a web page, you have to
add some display information
XML documents do not carry information about how to display the data
Different solutions to the display problem, using CSS, XSL, JavaScript, and XML Data Islands
Will you be writing your future Homepages in XML?
Displaying XML with CSS
With CSS (Cascading Style Sheets) you can add display information to an XML document
Formatting XML with CSS is NOT the future of the Web
Formatting with XSL will be the new standard
Example: the xml file
<?xml version="1.0" encoding="ISO-8859-1"?> <?xml-stylesheet type="text/css" href="cd_catalog.css"?> <CATALOG>
<CD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY>
<PRICE>10.90</PRICE> <YEAR>1985</YEAR>
</CD> <CD>
<TITLE>Hide your heart</TITLE> <ARTIST>Bonnie Tyler</ARTIST>
<COUNTRY>UK</COUNTRY> <COMPANY>CBS Records</COMPANY><PRICE>9.90</PRICE> <YEAR>1988</YEAR> </CD>
. . . . </CATALOG>
Example: the css file
CATALOG { background-color: #ffffff; width: 100%; }
CD { display: block; margin-bottom: 30pt; margin-left: 0; }
TITLE { color: #FF0000; font-size: 20pt; }
ARTIST{ color: #0000FF; font-size: 20pt; }
COUNTRY,PRICE,YEAR,COMPANY { Display: block; color: #000000; margin-left: 20pt; }
Displaying XML with XSL
With XSL you can add display information to your XML document
XSL is the preferred style sheet language of XML XSL (the eXtensible Stylesheet Language) is far
more sophisticated than CS One way to use XSL is to transform XML into HTML
before it is displayed by the browser
Example: the xml file
<?xml version="1.0" encoding="ISO-8859-1"?><?xml-stylesheet type="text/xsl" href="simple.xsl" ?><breakfast_menu>
<food><name>Belgian Waffles</name><price>$5.95</price><description>two of our famous Belgian Waffles with plenty of real maple syrup</description><calories>650</calories>
</food><food>
<name>Strawberry Belgian Waffles</name><price>$7.95</price><description>light Belgian waffles covered with strawberries and whipped cream</description><calories>900</calories>
</food>…</breakfast_menu>
</breakfast_menu>
Example: the xsl file
<?xml version="1.0" encoding="ISO-8859-1"?><html xsl:version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns="http://www.w3.org/TR/xhtml1/strict"> <body style="font-family:Arial,helvetica,sans-serif;font-size:12pt; background-color:#EEEEEE"> <xsl:for-each select="breakfast_menu/food"> <div style="background-color:teal;color:white;padding:4px"> <span style="font-weight:bold;color:white"> <xsl:value-of select="name"/></span> - <xsl:value-of select="price"/> </div> <div style="margin-left:20px;margin-bottom:1em;font-size:10pt"> <xsl:value-of select="description"/> <span style="font-style:italic"> (<xsl:value-of select="calories"/> calories per serving) </span> </div> </xsl:for-each> </body></html>
View the result in IE 6
XML Data Islands
XML can be embedded within HTML pages in Data Islands
Manipulated via client side script or data binding
The unofficial <xml> tag is used to embed XML data within HTML
Data Islands can be bound to HTML elements (like HTML tables)<html> <body> <xml id="cdcat" src="cd_catalog.xml"></xml> <table border="1" datasrc="#cdcat"> <tr> <td> <span datafld="ARTIST"> </span> </td> <td> <span datafld="TITLE"> </span> </td></tr> </table> </body> </html>
The Microsoft XML Parser
To read and update an XML document, you need an XML parser
The Microsoft XML parser comes with Microsoft Internet Explorer 5.0
Once you have installed IE 5.0, the parser is available to scripts, both inside HTML documents. The parser features a language-neutral programming model that
supports: JavaScript, VBScript, Perl, VB, Java, C++ and more W3C XML 1.0 and XML DOM DTD and validation
You can create an XML document object with the following code: var xmlDoc=new ActiveXObject("Microsoft.XMLDOM")
Loading an XML file into the parser
XML files can be loaded into the parser using script code.
The following code loads an XML document (note.xml) into the XML parser: <script type="text/javascript">
var xmlDoc = new ActiveXObject("Microsoft.XMLDOM") xmlDoc.async="false" xmlDoc.load("note.xml") // ....... processing the document goes here </script>
The second line in the code above creates an instance of the Microsoft XML parser
The third line turns off asynchronized loading, to make sure that the parser will not continue execution before the document is fully loaded
The fourth line tells the parser to load the XML document called note.xml
Namespaces: Overview
Part of XML’s extensibility
Allow authors to differentiate between tags of the same name (using a prefix) Frees author to focus on the data and decide how to
best describe it Allows multiple XML documents from multiple
authors to be merged
Identified by a URI (Uniform Resource Identifier) When a URL is used, it does NOT have to represent
a live server
Namespaces: Declaration
xmlns: bk = “http://www.example.com/bookinfo/”
xmlns: bk = “urn:mybookstuff.org:bookinfo”
Namespace declaration examples:
Namespace declaration Prefix URI (URL)
xmlns: bk = “http://www.example.com/bookinfo/”
Namespaces: Examples
<BOOK xmlns:bk=“http://www.bookstuff.org/bookinfo”> <bk:TITLE>All About XML</bk:TITLE> <bk:AUTHOR>Joe Developer</bk:AUTHOR> <bk:PRICE currency=‘US Dollar’>19.99</bk:PRICE>
<bk:BOOK xmlns:bk=“http://www.bookstuff.org/bookinfo”xmlns:money=“urn:finance:money”>
<bk:TITLE>All About XML</bk:TITLE> <bk:AUTHOR>Joe Developer</bk:AUTHOR> <bk:PRICE money:currency=‘US Dollar’> 19.99</bk:PRICE>
Namespaces: Default Namespace
An XML namespace declared without a prefix becomes the default namespace for all sub-elements
All elements without a prefix will belong to the default namespace:
<BOOK xmlns=“http://www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE> <AUTHOR>Joe Developer</AUTHOR>
Namespaces: Scope
Unqualified elements belong to the inner-most default namespace. BOOK, TITLE, and AUTHOR belong to the default
book namespace PUBLISHER and NAME belong to the default
publisher namespace
<BOOK xmlns=“www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE> <AUTHOR>Joe Developer</AUTHOR> <PUBLISHER xmlns=“urn:publishers:publinfo”> <NAME>Microsoft Press</NAME> </PUBLISHER></BOOK>
Namespaces: Attributes
Unqualified attributes do NOT belong to any namespace Even if there is a default namespace
This differs from elements, which belong to the default namespace
Entities
Entities provide a mechanism for textual substitution, e.g.
You can define your own entities
Parsed entities can contain text and markup
Unparsed entities can contain any data JPEG photos, GIF files, movies, etc.
Entity Substitution
< <
& &
CDATA
By default, all text inside an XML document is parsed
You can force text to be treated as unparsed character data by enclosing it in <![CDATA[ ... ]]>
Any characters, even & and <, can occur inside a CDATA
Whitespace inside a CDATA is (usually) preserved
The only real restriction is that the character sequence ]]> cannot occur inside a CDATA
CDATA is useful when your text has a lot of illegal characters (for example, if your XML document contains some HTML text)
Pure XML -- Instance Model
XML 1.0 Standard: no explicit data model only syntax of well-formed and valid (wrt. a DTD) documents
implicit data model: nested containers ("boxes within boxes") labeled ordered trees (=a semistructured data model) relational, object-oriented, other data: easy to encode
<A> <B>foo</B> <C>bar</C> <C>lab</C></A>
A
B C
"foo" "bar"
C:"bar"
A:
B: "foo"
C:"lab"
"lab"
C
children are ordered
c2b2a2
c3b3a3
c1b1a1
CBA
R Rtuple
A a1 /AB b1 /BC c1 /C
/tupletuple
A a2 /AB b2 /BC c2 /C
/tuple …
/R
R
tuple
A B Ca1 b1 c1
tuple
A B Ca2 b2 c2
tuple
A B Ca3 b3 c3
Example: Relational Data to XML
Adding Structure and Semantics
XML Document Type Definitions (DTDs): define the structure of "allowed" documents (i.e., valid wrt. a DTD) database schema => improve query formulation, execution, ...
XML Schema defines structure and data types allows developers to build their own libraries of interchanged
data types
XML Namespaces identify your vocabulary
XML Related Technologies I
XHTML - Extensible HTML
CSS - Cascading Style Sheets
XSL - Extensible Style Sheet Language XSL consists of three parts: XML Document Transformation (renamed
XSLT, see below), a pattern matching syntax (renamed XPath, see below), and a formatting object interpretation.
XSLT - XML Transformation XSLT is far more powerful than CSS. It can be used to transform XML
files into many different output formats.
XPath - XML Pattern Matching XPath is a language for addressing parts of an XML document. XPath
was designed to be used by both XSLT and XPointer.
XML Related Technologies II
XLink - XML Linking Language The XML Linking Language (XLink), allows elements to be inserted
into XML documents in order to create links between XML resources.
XPointer - XML Pointer Language The XML Pointer Language (XPointer), supports addressing into the
internal structures of XML documents, such as elements, attributes, and content.
DTD - Document Type Definition A DTD can be used to define the legal building blocks of an XML
document.
Namespaces XML namespaces defines a method for defining element and attribute
names used in XML by associating them with URI references.
XML Related Technologies III
DOM - Document Object Model The DOM defines interfaces, properties and methods to
manipulate XML documents.
XSD - XML Schema Schemas are powerful alternatives to DTDs. Schemas are
written in XML, and support namespaces and data types.
XQL - XML Query Language The XML Query Language supports query facilities to extract
data from XML documents.
SAX - Simple API for XML SAX is another interface to read and manipulate XML
documents
References
W3 Schools XML Tutorial http://www.w3schools.com/xml/default.asp
W3C XML page http://www.w3.org/XML/
XML Tutorials http://www.programmingtutorials.com/xml.aspx
Online resource for markup language technologies http://xml.coverpages.org/
Several Online Presentations
Reading List
W3 Schools XML Tutorial http://www.w3schools.com/xml/default.asp