XML - Extensible Markup Language

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XML - Extensible Markup Language

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HTML - Hypertext Markup Language

HTML has a fixed tag set. Use these tags to describe how information is to be

presented. e.g. <H1>My Header</H1> Example - next slide

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<HTML><HEAD><TITLE>My HTML Table</TITLE></HEAD><BODY><H1><CENTER>My HTML Table</CENTER></H1><Table border><TR><TH>name</TH><TH>E-mail address</TH></TR><TR><TD>Jessica</FONT></TD><TD>[email protected]</TR></TR><TR><TD>Peter</TD><TD>[email protected]</TD></TR><TR><TD>Alen</FONT></TD><TD>[email protected]</FONT></TD></TR></Table></BODY></HTML>

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HTML Example Viewed in Browser

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HTML Example - Advantages

It's fairly readable. The HTML can be displayed by just about any

HTML browser, HOWEVER -- The meaning of the various

pieces of data in the document is lost.

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HTML: Not Suitable for Powerful Information Systems HTML isn't extensible HTML is very display-centric HTML isn't usually directly reusable HTML only provides one 'view' of data HTML has little or no semantic structure

How do we get a language that's roughly as easy to use as HTML but has none of these disadvantages?

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XML - Extensible Markup Language

XML, unlike HTML, is really a meta-language for describing markup languages. That is, XML provides a facility to define tags and the structural relationships between these tags.

User-defined tags Defines "what" is in the data instead of how the

data to be presented. Why is XML useful?

– Neutral Source of data (text format, structured)– Easy data format transformation

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XML and E-Commerce Has the potential for transferring data between

enterprises with different computer and DB systems. Fundamental to e-commerce.

A BConversion ConversionXML

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XML Notation

Meaning of data is clearly stated No display information Data in tags:

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XML Example<?xml version="1.0"?>

<XML ID="XMLID">

<class>

<student ID="0001" >

<name>Jessica</name>

<email>[email protected]</email>

</student>

<student ID="0002" >

<name>Peter</name>

<email>[email protected]</email>

</student>

</class>

</XML>

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Creating XML Can use text editor Save file as *.xml Can view in browser or use the data

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XML Document must be Well-Formed No unclosed tags Every start tag must have a corresponding end tag. No overlapping tags

<Tomato>

Let's call <Potato>the whole thing off</Tomato>

</Potato> Attribute values must be enclosed in quotes. Parsers can check for this. Can also have parsers

that validate that the structure and number of tags make sense.

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XML

Straightforward concept. Can be used:

– View data in a browser• Can alter appearance with Cascading Style

Sheets (CSS) or with Extensible Stylesheet Language (XSL)

– Manipulate data– Placed in an application e.g. database,

spreadsheet

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Cascading Style Sheets Have file containing formatting information (can also

include in HTML file). Example (see next page for details):

Mylabel_1 {display: block;}Mylabel_2 {display: block;}Mylabel_3 {display: block;}Mylabel_4 {display: block;}

Save as a file named "mycssadv.css" in the same directory of the xml file

Add this line to the XML file below the <?xml version="1.0"?> statement:

<?xml-stylesheet type="text/css" href="mycssadv.css" ?>

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class { display: block;border: 2px solid black;padding: 1em;background-color: #888833;color: #FFFFDD;font-family: Times, serif;font-style: italic;text-align: center;}

student { display: block;border: 2px solid black;padding: 1em;background-color: #008833;color: #FFFFFF;font-family: Times, serif;font-style: italic;text-align: center;}

name { display: block;border: 0px solid black;padding: 1em;

background-color: #008833;color: #FFDDAA;font-family: Times, serif;font-style: italic;text-align: center;}

email {display: block;}

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Viewing XML with Example CSS

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CSS - Detailed Information

http://www.w3.org/TR/REC-CSS1

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CSS

Cascading style sheets styles (like fonts, colors, and so on) for one

markup element "cascade" down, and apply to all of the element's contents.

Can be a separate file. Limited to “styling” a file.

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XSL (Extensible Stylesheet Language)

XSL can: Specify display characteristics Convert XML through querying,

sorting and filtering

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XML and XSL

XML XSL BROWSER

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Example XSL file (using an HTML template)

<?xml version="1.0" ?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"><xsl:template match="/"><HTML><BODY><TABLE BORDER="2"><TR><TD>Name</TD> <TD>E-mail Address</TD> </TR><xsl:for-each select="XML/class/student" ><TR><TD><xsl:value-of select="name" /></TD><TD><xsl:value-of select="email" /></TD></TR></xsl:for-each></TABLE></BODY></HTML></xsl:template></xsl:stylesheet>

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View Results

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Advanced Features: Sorting with an XSL file Modify the xsl file:

<xsl:for-each select="XML/class/student" order-by="email">

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XML and XSL

XML XSL BROWSER

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XSL: Extended Style Language Can style a file Can also restructure a file See example Builds an html page from XML code XSL's design also includes embedded

scripting (JavaScript) - limited implementation of this

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Modeling information structure in XML

XML forms a structure. The Document Object Model (DOM) Level 1

Recommendation describes a set of language-neutral interfaces capable of representing any well-formed XML or HTML document.

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DOM

Use of DOM allows program or script to use the XML or HTML

Dynamic HTML is an example The DOM opens the door to using XML as

the lingua franca of data interchange on the Internet, and even within applications.

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SAX

The easiest way to process an XML file in Java is by using the Simple API for XML, or SAX.

SAX is a simple Java interface that many Java parsers can use.

A SAX parser is a class that implements the interface org.xml.sax.Parser

This parser "walks" the tree of document nodes in an XML file, calling the methods of user-defined handler classes.

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Using XML

A BConversion/

ProgramConversion/

Program

XML

•Can present data differently•Can add to database•Can have program manipulate data

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Further XML Information

http://msdn.microsoft.com/xml/default.asp

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Document Type Definition While a well-formed document is well-formed because

it follows rules defined by the XML spec, a valid document is valid because it matches its document type definition (DTD).

The DTD is the grammar for a markup language, defined by the designer of the markup language.

The DTD specifies: – what elements may exist,

– what attributes the elements may have,

– what elements may or must be found inside other elements, and in what order.

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DTD

The DTD defines the document type. DTDs currently are being written for an

enormous number of different problem domains, and each DTD defines a new markup language.

Determining a DTD is an essential step in using XML for e-commerce

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See readings for explanation

<!ELEMENT Recipe (Name, Description?, Ingredients?, Instructions?)>

<!ELEMENT Name (#PCDATA)>

<!ELEMENT Description (#PCDATA)>

<!ELEMENT Ingredients (Ingredient)*>

<!ELEMENT Ingredient (Qty, Item)>

<!ELEMENT Qty (#PCDATA)>

<!ATTLIST Qty unit CDATA #REQUIRED>

<!ELEMENT Item (#PCDATA)>

<!ATTLIST Item optional CDATA "0"

isVegetarian CDATA "true">

<!ELEMENT Instructions (Step)+>

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DTD

Parser can check if XML code is following DTD.

A DTD is associated with an XML document by way of a document type declaration, which appears at the top the XML file (after the <?xml...?> line).

For example:

<!DOCTYPE Recipe SYSTEM "example.dtd">

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XML Schema

defines elements that can appear in a document defines attributes that can appear in a document defines which elements are child elements defines the order of child elements defines the number of child elements defines whether an element is empty or can include

text defines data types for elements and attributes defines default and fixed values for elements and

attributes

From http://www.w3schools.com/schema/schema_intro.asp

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XML Schemas are the Successors of DTDs

It is thought that very soon XML Schemas will be used in most Web applications as a replacement for DTDs. Here are some reasons:

XML Schemas are extensible to future additions XML Schemas are richer and more useful than DTDs XML Schemas are written in XML XML Schemas support data types XML Schemas support namespaces


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XML Schema has Support for Data Types

One of the greatest strengths of XML Schemas is the support for data types. With the support for data types:

It is easier to describe permissible document content It is easier to validate the correctness of data It is easier to work with data from a database It is easier to define data facets (restrictions on data) It is easier to define data patterns (data formats) It is easier to convert data between different data

types


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XML Schemas Secure Data Communication

When data is sent from a sender to a receiver it is essential that both parts have the same "expectations" about the content.

With XML Schemas, the sender can describe the data in a way that the receiver will understand.

A date like this: "03-11-2004" will, in some countries, be interpreted as 3. November and in other countries as 11. March, but an XML element with a data type like this:

<date type="date">2004-03-11</date> ensures a mutual understanding of the content because the

XML data type date requires the format YYYY-MM-DD.


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Schemas and DTD

Short term DTDs have advantages:– Widespread tools support. All SGML tools and

many XML tools can process DTDs.– Widespread deployment. A large number of

document types are already defined using DTDs: HTML, XHTML, DocBook, TEI, J2008, CALS, etc.

– Widespread expertise and many years of practical application.

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Schemas and DTDs DTDs:

– They are written in a different (non-XML) syntax.

– They have no support for namespaces.

– They only offer extremely limited datatyping. No facility for describing numbers, dates, currency values, and so forth. Furthermore, DTDs have no ability to express the datatype of character data in elements.

– They have a complex and fragile extension mechanism based on little more than string substitution.

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Benefits of Representing Information in XML

XML is at least as readable as HTML and probably more so. The tags don't have anything to do with how the document is

displayed. Separation of content and presentation is a key concept

inherited from SGML. XML is more versatile than HTML A lot of the programming is already done for you

– If you write a DTD and use a validating parser, much of the error checking for the validity of your input is done by the parser. There's no need to write the parser yourself, since there are so many high-quality parsers available for free.

XML - Extensible Markup Language

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