XML and XSL

What is XML?

XML (eXtensible markup language) is all about describing data.
<?xml version=“1.0” encoding=“ISO-8859-1”?>
<products>

<productname>Shoes</productname>
<qty>12</qty>
<totalcost>100</totalcost>
<discount>10</discount>

</products>

An XML tag is not something predefined but it is something you have to define according to your needs. For instance in the above example of <products> all tags are defined according to business needs.

The XML document is self explanatory, any one can easily understand looking at the XML data what exactly it means.

“Version” tag shows which version is XML is used.
What is ROOT element in XML?

In the above sample example <products></products> tag is the root element. Root element is the top most element for a XML.

All the tags should have the closing tag otherwise it will not work.
XML is case sensitive.

What is the difference between XML and HTML?
XML describes the data and HTML describes how the data should be displayed.

Is XML meant to replace HTML?
No, they both go together XML for describe DATA and HTML for displaying data.

Why we are using XML files in our applications?
XML files is use for exchanging a data and any two different application can read the data from the xml file.

DTD(Document Type Definition) it is used to defines how your XML should structure. DOM is a W3C recommended way for treating XML documents. In DOM we load entire XML document into memory and allows us to manipulate the structure and data of XML document.

CDATA section in XML is used for if you want to exclude some elements you will need to put those elements in CDATA.

<product itemnumber=“d123” > </product>
In above example product is an element and itemnumber is an attribute.

XML Parser

XML parser sits in between the XML document and the application who want to use the XML document. Parser exposes set of well defined interfaces which can be used by the application for adding, modifying and deleting the XML document contents. Now whatever interfaces XML parser exposes should be standard or else that would lead to different vendors preparing there own custom way of interacting with XML document.

There are two standard specifications which are very common and should be followed by a XML parser.

DOM (Document Object Model)
SAX (Simple API for XML)

DOM Parser loading XML document

SAX (Simple API for XML)

SAX parser does not load the whole DOM in to memory but has event based approach.
It parsing the XML File emits events.
It only sends those events to the application which is register to the SAX parser.

XML in Dot Net (Using System.xml)

Provides standards-based support for processing XML
It Includes classes, Interfaces, Delegates, Enumerations

System.Xml Namespace -- Classes

Class	Description
NameTable	Implements a single-threaded XmlNameTable.
UniqueId	A unique identifier optimized for Guids.
XmlAttribute	Represents an attribute. Valid and default values for the attribute are defined in a document type definition (DTD) or schema.
XmlAttributeCollection	Represents a collection of attributes that can be accessed by name or index. XmlAttributeCollection extends the XmlNamedNodeMap class adding strongly typed helper methods. You can use this class to add, remove or modify attributes in the collection. XmlAttributeCollection is returned by the XmlElement.Attributes property.
XmlBinaryReaderSession	Enables optimized strings to be managed in a dynamic way.
XmlBinaryWriterSession	Enables using a dynamic dictionary to compress common strings that appear in a message and maintain state.
XmlCDataSection	Represents a CDATA section.
XmlCharacterData	Provides text manipulation methods that are used by several classes.
XmlComment	Represents the content of an XML comment.
XmlConvert	Encodes and decodes XML names and provides methods for converting between common language runtime types and XML Schema definition language (XSD) types. When converting data types the values returned are locale independent.
XmlDataDocument	Allows structured data to be stored, retrieved, and manipulated through a relational DataSet.
XmlDeclaration	Represents the XML declaration node <?xml version='1.0'...?>.
XmlDictionary	Implements a dictionary used to optimize Windows Communication Foundation (WCF)'s XML reader/writer implementations.
XmlDictionaryReader	An abstract class that the Windows Communication Foundation (WCF) derives from to do serialization and deserialization.
XmlException	Returns detailed information about the last exception.
XmlImplementation	Defines the context for a set of XmlDocument objects.
XmlLinkedNode	Gets the node immediately preceding or following this node.
XmlNamedNodeMap	Represents a collection of nodes that can be accessed by name or index.
XmlNamespaceManager	Resolves, adds, and removes namespaces to a collection and provides scope management for these namespaces.
XmlNameTable	Table of atomized string objects.
XmlNode	Represents a single node in the XML document.
XmlNodeChangedEventArgs	Provides data for the NodeChanged, NodeChanging, NodeInserted, NodeInserting, NodeRemoved and NodeRemoving events.
XmlNodeList	Represents an ordered collection of nodes.
XmlNodeReader	Represents a reader that provides fast, non-cached forward only access to XML data in an XmlNode.
XmlNotation	Represents a notation declaration, such as <!NOTATION... >.
XmlParserContext	Provides all the context information required by the XmlReader to parse an XML fragment.
XmlProcessingInstruction	Represents a processing instruction, which XML defines to keep processor-specific information in the text of the document.
XmlQualifiedName	Represents an XML qualified name.
XmlReader	Represents a reader that provides fast, non-cached, forward-only access to XML data.
XmlReaderSettings	Specifies a set of features to support on the XmlReader object created by the Create method.
XmlResolver	Resolves external XML resources named by a Uniform Resource Identifier (URI).
XmlTextWriter	Represents a writer that provides a fast, non-cached, forward-only way of generating streams or files containing XML data that conforms to the W3C Extensible Markup Language (XML) 1.0 and the Namespaces in XML recommendations.
XmlUrlResolver	Resolves external XML resources named by a Uniform Resource Identifier (URI).
XmlValidatingReader	Obsolete. Represents a reader that provides document type definition (DTD), XML-Data Reduced (XDR) schema, and XML Schema definition language (XSD) validation.
XmlWhitespace	Represents white space in element content.
XmlWriter	Represents a writer that provides a fast, non-cached, forward-only means of generating streams or files containing XML data.
XmlDocument	Represents an attribute. Valid and default values for the attribute are defined in a DTD or schema. The XmlElement class has several methods which allow you to access attribute nodes (XmlElement.GetAttribute, XmlElement.SetAttribute, XmlElement.RemoveAttribute, and so on). Additionally, you can call the XmlElement.Attributes property which returns an XmlAttributeCollection enabling you to access attributes by name or index from the collection.
XmlDocumentFragment	Represents a lightweight object that is useful for tree insert operations.
XmlDocumentType	Represents the document type declaration.
XmlElement	Represents an element.
XmlEntity	Represents an entity declaration, such as <!ENTITY... >.
XmlEntityReference	Represents an entity reference node.
XmlDictionaryReaderQuotas	Contains configurable quota values for XmlDictionaryReaders.
XmlDictionaryString	Represents an entry stored in a XmlDictionary.
XmlDictionaryWriter	An abstract class that the Windows Communication Foundation (WCF) derives from to do serialization and deserialization.
XmlSecureResolver	Helps to secure another implementation of XmlResolver by wrapping the XmlResolver object and restricting the resources that the underlying XmlResolver has access to.
XmlSignificantWhitespace	Represents white space between markup in a mixed content node or white space within an xml:space= 'preserve' scope. This is also referred to as significant white space.
XmlText	Represents the text content of an element or attribute.
XmlTextReader	Represents a reader that provides fast, non-cached, forward-only access to XML data.
XmlWriterSettings	Specifies a set of features to support on the XmlWriter object created by the XmlWriter..::.Create method.

System.Xml Namespace -- Interface

Interface	Description
IFragmentCapableXmlDictionaryWriter	Contains properties and methods that when implemented by a XmlDictionaryWriter, allows processing of XML fragments.
IHasXmlNode	Enables a class to return an XmlNode from the current context or position.
IStreamProvider	An interface that can be implemented by classes providing streams.
IXmlBinaryReaderInitializer	Provides methods for reinitializing a binary reader to read a new document.
IXmlBinaryWriterInitializer	Specifies implementation requirements for XML binary writers that derive from this interface.
IXmlDictionary	An interface that defines the contract that an Xml dictionary must implement to be used by XmlDictionaryReader and XmlDictionaryWriter implementations.
IXmlLineInfo	Provides an interface to enable a class to return line and position information.
IXmlMtomReaderInitializer	Specifies implementation requirements for XML MTOM readers that derive from this interface.
IXmlMtomWriterInitializer	When implemented by an MTOM writer, this interface ensures initialization for an MTOM writer.
IXmlNamespaceResolver	Provides read-only access to a set of prefix and namespace mappings.
IXmlTextReaderInitializer	Specifies implementation requirements for XML text readers that derive from this interface.
IXmlTextWriterInitializer	Specifies implementation requirements for XML text writers that derive from this interface.

System.Xml Namespace -- Delegate

Delegate	Description
OnXmlDictionaryReaderClose	delegate for a callback method when closing the reader.
XmlNodeChangedEventHandler	Represents the method that handles

System.Xml Namespace -- Enumeration

Enumeration	Description
ConformanceLevel	Specifies the amount of input or output checking that the created XmlReader and XmlWriter objects perform.
EntityHandling	Specifies how the XmlTextReader or XmlValidatingReader handle entities.
Formatting	Specifies formatting options for the XmlTextWriter.
NewLineHandling	Specifies how to handle line breaks.
ReadState	Specifies the state of the reader.
ValidationType	Specifies the type of validation to perform.
WhitespaceHandling	Specifies how white space is handled.
WriteState	Specifies the state of the XmlWriter.
XmlDateTimeSerializationMode	Specifies how to treat the time value when converting between string and DateTime.
XmlNamespaceScope	Defines the namespace scope.
XmlNodeChangedAction	Specifies the type of node change.
XmlNodeOrder	Describes the document order of a node compared to a second node.
XmlNodeType	Specifies the type of node.
XmlOutputMethod	Specifies the method used to serialize the XmlWriter output.
XmlSpace	Specifies the current xml:space scope.
XmlTokenizedType	Represents the XML type for the string. This allows the string to be read as a particular XML type, for example a CDATA section type.

XPath in Dot Net (Using System.Xml.XPath )

System.Xml.XPath Namespace
System.Xml.XPath namespace contains the interfaces, enumerations, classes that defines a cursor model for navigating and editing XML information.

Classes

XPathDocument
XPathException
XPathExpression
XPathItem
XPathNavigator
XPathNodeIterator

Interfaces

IXPathNavigable

Enumerations

XmlCaseOrder
XmlDataType
XmlSortOrder
XPathNamespaceScope
XPathNodeType
XPathResultType

System.Xml.XPath Namespace -- Classes

Class	Description	Declaration
XPathDocument	Provides a fast, read-only, in-memory representation of an XML document using the XPath data model.	Dim instance As XPathDocument
XPathException	Provides the exception thrown when an error occurs while processing an XPath expression.	Dim instance As XPathException
XPathExpression	Provides a typed class that represents a compiled XPath expression.	Dim instance As XPathExpression
XPathItem	Represents an item in the XQuery 1.0 and XPath 2.0 Data Model.	Dim instance As XPathItem
XPathNavigator	Provides a cursor model for navigating and editing XML data.	Dim instance As XPathNavigator
XPathNodeIterator	Provides an iterator over a selected set of nodes.	Dim instance As XPathNodeIterator

System.Xml.XPath Namespace -- Interface

Interface	Description	Declaration
IXPathNavigable	Provides an accessor to the XPathNavigator class.	Dim instance As IXPathNavigable

System.Xml.XPath Namespace -- Enumeration

Enumeration	Description	Declaration
XmlCaseOrder	Specifies the sort order for uppercase and lowercase letters.	Dim Instance As XmlCaseOrder
XmlDataType	Specifies the data type used to determine sort order.	Dim Instance As XmlDataType
XmlSortOrder	Specifies the sort order.	Dim Instance As XmlSortOrder
XPathNamespaceScope	Defines the namespace scope.	Dim Instance As XPathNamespaceScope
XPathNodeType	Defines the XPath node types that can be returned from the XPathNavigator class.	Dim Instance As XPathNodeType
XPathResultType	Specifies the return type of the XPath expression.	Dim Instance As XPathResultType

What is XSL?

XSL (the eXtensible Stylesheet Language) is used to transform XML document to some other document. It transform the document which can convert XML to some other document. If we apply XSL to XML it convert it to HTML document output.

HTML pages uses predefined tags, and the meaning of these tags is well understood: <p> means a paragraph and <h1> means a header, and the browser knows how to display these pages.

With XML we can use any tags we want, and the meaning of these tags are not automatically understood by the browser: <table> could mean a HTML table or maybe a piece of furniture. Because of the nature of XML, there is no standard way to display an XML document.

In order to display XML documents, it is necessary to have a mechanism to describe how the document should be displayed. One of these mechanisms is Cascading Style Sheets (CSS), but XSL (eXtensible Stylesheet Language) is the preferred style sheet language of XML, and XSL is far more sophisticated than the CSS used by HTML.

XSL Architecture

The World Wide Web Consortium (W3C) issued the XSL transformations, or XSLT for short, as a recommendation - a type of W3C standard. The purpose of this language, written in XML, is to allow webmasters and programmers to take XML data with any desired structure and use them to generate something which the server can supply to the user as an HTML page.

The processing of XML sources via an XSLT program basically means that the latter uses the source to generate a document tree and converts this to a result tree by executing the instructions specified in the stylesheet.

XSL consists of two parts:

A method for transforming XML documents
A method for formatting XML documents

XSL as a language that can transform XML into HTML, a language that can filter and sort XML data and a language that can format XML data, based on the data value, like displaying negative numbers in red.

XSL can be used to define how an XML file should be displayed by transforming the XML file into a format that is recognizable to a browser. One such format is HTML. Normally XSL does this by transforming each XML element into an HTML element.

XSL can also add completely new elements into the output file, or remove elements. It can rearrange and sort the elements, test and make decisions about which elements to display.

Transforming XML to HTML

XML File sample.xml
<?xml version="1.0" encoding="ISO8859-1" ?>
<CATALOG>
<CD>
<TITLE>Empire Burlesque</TITLE>
<ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE>
<YEAR>1985</YEAR>
</CD>
</CATALOG>

XSL File sample.xsl
<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
<html>
<body>
<table border="2" bgcolor="yellow">
<tr> <th>Title</th> <th>Artist</th> </tr>
<xsl:for-each select="CATALOG/CD">
<tr>
<td><xsl:value-of select="TITLE"/></td>
<td><xsl:value-of select="ARTIST"/></td>
</tr>
</xsl:for-each>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

In the above file, the xsl:for-each element locates elements in the XML document and repeats a template for each one. The select attribute describes the element in the source document. The syntax for this attribute is called an XSL Pattern, and works like navigating a file system where a forward slash (/) selects subdirectories. The xsl:value-of element selects a child in the hierarchy and inserts the content of that child into the template.

Since an XSL style sheet is an XML file itself, the file begins with an xml declaration. The xsl:stylesheet element indicates that this document is a style sheet. The template has also been wrapped with xsl:template match="/" to indicate that this is a template that corresponds to the root (/) of the XML source document.

XSL - On the Client

HTML File sample.html
<html>
<body>
<script language="javascript">
// Load XML
var xml = new ActiveXObject("Microsoft.XMLDOM")
xml.async = false xml.load(“sample.xml")
// Load the XSL
var xsl = new ActiveXObject("Microsoft.XMLDOM")
xsl.async = false xsl.load("sample.xsl")
// Transform
document.write(xml.transformNode(xsl))
</script>
</body>
</html>

The first block of code creates an instance of the Microsoft XML parser (XMLDOM), and loads the XML document into memory. The second block of code creates another instance of the parser and loads the XSL document into memory. The last line of code transforms the XML document using the XSL document, and writes the result to the HTML document.

XSL - Sort

<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
<html>
<body>
<table border="2" bgcolor="yellow">
<tr> <th>Title</th> <th>Artist</th></tr>
<xsl:for-each select="CATALOG/CD" order-by="+ ARTIST">
<tr>
<td><xsl:value-of select="TITLE"/></td>
<td><xsl:value-of select="ARTIST"/></td>
</tr>
</xsl:for-each>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

To output this XML file as an ordinary HTML file, and sort it at the same time, simply add an order-by attribute to your for-each element like this:

<xsl:for-each select="CATALOG/CD" order-by="+ ARTIST">
The order-by attributes takes a plus (+) or minus (-) sign, to define an ascending or descending sort order, and an element name to define the sort element.

<html>
<body>
<script language="javascript">
// Load XML
var xml = new ActiveXObject("Microsoft.XMLDOM")
xml.async = false xml.load(“sample.xml")
// Load the XSL
var xsl = new ActiveXObject("Microsoft.XMLDOM")
xsl.async = false xsl.load(“sample.xsl")
// Transform
document.write(xml.transformNode(xsl))
</script>
</body>
</html>

XSL - Filter Query

Legal filter operators are:
= (equal)
=! (not equal)
&LT& less than
&GT& greater than

<xsl:for-each select="CATALOG/CD[ARTIST='Bob Dylan']"> <tr> <td><xsl:value-of select="TITLE"/></td> <td><xsl:value-of select="ARTIST"/></td> </tr> </xsl:for-each>

XSL - Conditional If

<xsl:for-each select="CATALOG/CD">
<xsl:if match=".[ARTIST='Bob Dylan']">
<tr>
<td><xsl:value-of select="TITLE"/></td> <td><xsl:value-of select="ARTIST"/></td>
</tr>
</xsl:if>
</xsl:for-each>

To put an conditional if test against the content of the file, simply add an xsl:if element to your XSL document like this:
<xsl:if match=".[ARTIST='Bob Dylan']">... some output ...</xsl:if>

XSL - Conditional Choose

<xsl:for-each select="CATALOG/CD">
<tr>
<td><xsl:value-of select="TITLE"/></td>
<xsl:choose>
<xsl:when match=".[ARTIST='Bob Dylan']">
<td bgcolor="#ff0000">
<xsl:value-of select="ARTIST"/></td>
</xsl:when>
<xsl:otherwise>
<td><xsl:value-of select="ARTIST"/></td>
</xsl:otherwise>
</xsl:choose>
</tr>
</xsl:for-each>

To insert an conditional choose test against the content of the file, simply add an xsl:choose, xsl:when and xsl:otherwise elements to your XSL document like this:
<xsl:choose> <xsl:when match=".[ARTIST='Bob Dylan']"> ... some code ... </xsl:when> <xsl:otherwise> ... some code .... </xsl:otherwise></xsl:choose>

Transforming it on the Client

<html>
<body>
<script language="javascript">
// Load XML
var xml = new ActiveXObject("Microsoft.XMLDOM")
xml.async = false xml.load("cd_catalog.xml")
// Load the XSL
var xsl = new ActiveXObject("Microsoft.XMLDOM")
xsl.async = false xsl.load("cd_catalog_filter.xsl")
// Transform
document.write(xml.transformNode(xsl))
</script>
</body>
</html>

XSL in Dot Net (Using System.xml.Xsl)

The System.Xml.Xsl namespace provides support for Extensible Stylesheet Transformation (XSLT) transforms.
It Includes classes, Interfaces, Delegates

System.Xml.Xsl Namespace -- Classes

Class		Description	Declaration
XslCompiledTransform		Transforms XML data using an XSLT style sheet.	Dim instance As XslCompiledTransform
Methods	Equals	Overloaded. Determines whether two Object instances are equal. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. GetHashCode is suitable for use in hashing algorithms and data structures like a hash table. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	Load	Overloaded. Compiles the style sheet.
	ReferenceEquals	Determines whether the specified Object instances are the same instance. (Inherited from Object.)
	ToString	Returns a String that represents the current Object. (Inherited from Object.)
	Transform	Overloaded. Executes the XSLT transformation.
Properties	OutputSettings	Gets an XmlWriterSettings object that contains the output information derived from the xsl:output element of the style sheet.
Properties	TemporaryFiles	Gets the TempFileCollection that contains the temporary files generated on disk after a successful call to the Load method.
Protected Methods	Finalize	Allows an Object to attempt to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Protected Methods	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)

Class		Description	Declaration
XslCompiledTransform		Transforms XML data using an XSLT style sheet.	Dim instance As XslCompiledTransform
Methods	Equals	Overloaded. Determines whether two Object instances are equal. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. GetHashCode is suitable for use in hashing algorithms and data structures like a hash table. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	Load	Overloaded. Compiles the style sheet.
	ReferenceEquals	Determines whether the specified Object instances are the same instance. (Inherited from Object.)
	ToString	Returns a String that represents the current Object. (Inherited from Object.)
	Transform	Overloaded. Executes the XSLT transformation.
Properties	OutputSettings	Gets an XmlWriterSettings object that contains the output information derived from the xsl:output element of the style sheet.
Properties	TemporaryFiles	Gets the TempFileCollection that contains the temporary files generated on disk after a successful call to the Load method.
Protected Methods	Finalize	Allows an Object to attempt to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Protected Methods	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
Protected Methods	Finalize	Allows an Object to attempt to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Protected Methods	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
Public Events	XsltMessageEncountered	Occurs when a message is specified in the style sheet by the xsl:message element.

XsltCompileException		The exception that is thrown by the Load method when an error is found in the XSLT style sheet.
Public Properties	Data	Gets a collection of key/value pairs that provide additional, user-defined information about the exception.(Inherited from Exception.)
	HelpLink	Gets or sets a link to the help file associated with this exception.(Inherited from Exception.)
	InnerException	Gets the Exception instance that caused the current exception.(Inherited from Exception.)
	LineNumber	Gets the line number indicating where the error occurred in the style sheet.(Inherited from XsltException.)
	LinePosition	Gets the line position indicating where the error occurred in the style sheet.(Inherited from XsltException.)
	Message	Gets the formatted error message describing the current exception.(Inherited from XsltException.)
	Source	Gets or sets the name of the application or the object that causes the error.(Inherited from Exception.)
	SourceUri	Gets the location path of the style sheet.(Inherited from XsltException.)
	StackTrace	Gets a string representation of the frames on the call stack at the time the current exception was thrown.(Inherited from Exception.)
	TargetSite	Gets the method that throws the current exception.(Inherited from Exception.)
	HResult	Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.(Inherited from Exception.)