xml 1 enterprise applications ce00465-m xml. 2 enterprise applications ce00465-m xml overview...

Enterprise Applications CE00465-MXML 1

XML


XML Overview

• Extensible Mark-up Language (XML) is a meta-language that describes the content of the document (self-describing data)

Java = Portable Programs

XML = Portable Data

• XML does not specify the tag set or grammar of the language– Tag Set: mark-up tags that have meaning to a language processor

– Grammar: defines correct usage of a language’s tags


Applications of XML

• Configuration files– Used extensively in J2EE architectures

• Media for data interchange– A better alternative to proprietary data formats

• Business-to-business (B2B) transactions on the Web– Electronic business orders (ebXML)

– Financial Exchange (IFX)

– Messaging exchange (SOAP)


XML versus HTML

• XML fundamentally separates content (data and language) from presentation; HTML allows a mix of content and presentation

• HTML explicitly defines a set of legal tags as well as the grammar (intended meaning)– <TABLE>…<TABLE>

• XML allows any tags or grammar to be used hence eXtensible– <STUDENT>…</STUDENT>

• Note: Both are based on Standard Generalized Markup Language (SGML)


Simple XML Example

Student.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE XmlStudents SYSTEM "Student.dtd"><XmlStudents> <XmlStudent>

<img src="harry.gif"></img> <StdNo>2</StdNo> <FirstName>Harry</FirstName> <LastName>Nelson</LastName> <Phone>250</Phone> <StartDate>2005-09-28</StartDate> <Award>Computer Science</Award> <Faculty>VP</Faculty> </XmlStudent></XmlStudents>


Parsers & well-formed XML Documents

• A software program called an XML parser (or an XML processor) is required to process an XML document

– Parser reads the documents, checks its syntax and reports any errors

– XML documents are well formed if they are syntactically correct

– XML documents requires a single root element, start and end tag for each element, properly nested tags and attribute values in quotes

– Parsers can support either the Document Object Model (DOM) and/or Simple API for XML (SAX)


XML Components

• Prolog– Defines the xml version, entity definitions and DOCTYPE

• Components of the document– Tags and attributes

– CDATA (character data)

– Entities

– Processing instructions

– Comments


XML prolog

• XML Files always start with a prolog

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE XmlStudents SYSTEM “Students.dtd">

– The version of XML is required

– The encoding identifies the character set

– The prolog can contain entities and DTD definitions


Document Type Definitions (DTDs)

• Introduced into an XML document by !DOCTYPE statement– DTDs define an XML document’s structure (i.e. what elements are

allowed in the document)

– An XML document doesn’t have to have a DTD

– But are often recommended to ensure document conformity• especially in B2B transactions

• Parsers are classified as validating or non-validating.

• Validating parsers check the XML document against the DTD– If the XML document conforms to the DTD it is said to be valid

– If it fails to conform to the DTD but is syntactically correct it is said to be well formed

– A valid document must also be well formed


Example of a DTD

Student.dtd

<?xml version="1.0" encoding="UTF-8"?><!ELEMENT XmlStudents (XmlStudent+)><!ELEMENT XmlStudent (img,StdNo,FirstName,LastName,Phone, StartDate,Award,Faculty)><!ELEMENT img (#PCDATA)><!ELEMENT StdNo (#PCDATA)><!ELEMENT FirstName (#PCDATA)><!ELEMENT LastName (#PCDATA)><!ELEMENT Phone (#PCDATA)><!ELEMENT StartDate (#PCDATA)><!ELEMENT Award (#PCDATA)><!ELEMENT Faculty (#PCDATA)>


Defining Elements

• <!ELEMENT name definition/type><!ELEMENT XmlStudents (XmlStudent+)><!ELEMENT XmlStudent (img,StdNo,FirstName,LastName,Phone,StartDate, Award,Faculty)><!ELEMENT img (#PCDATA)>

• Types– EMPTY Element cannot contain any text or child elements

– #PCDATA Only character data permitted

– ANY Any well-formed XML data

– List of legal child elements (no character data)

– May contain character data and/or child elements (cannot define order and number of child elements)


Defining Elements

• Cardinality– [none] Default (one and only one instance)

– ? 0,1

– * 0,1,…..,N

– + 1,2,…..,N

• List Operators– , Sequence (in order)

– | Choice (one of several)


Grouping Elements

• Set of elements can be grouped within parentheses– (Elem1?, Elem2?)+

• Elem1 can occur 0 or 1 times followed by 0 or 1 occurrences of Elem2• The group (sequence) must occur 1 or more times

• OR– ((Elem1, Elem2) | Elem3)*

• Either the group of Elem1, Elem2 is present (in order) or Elem3 is present, 0 or more times


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE Person[<!ELEMENT Person ( (Mr|Ms|Miss)?, FirstName, MiddleName*,

LastName,(Jr|Sr)? )><!ENTITY FirstName (#PCDATA)><!ENTITY MiddleName (#PCDATA)><!ENTITY LastName (#PCDATA)><!ENTITY Mr EMPTY><!ENTITY Ms EMPTY><!ENTITY Jr EMPTY><!ENTITY Sr EMPTY>]><Person> <Mr/> <FirstName>Harry</FirstName> <LastName>Nelson</LastName></Person>

Element Example

Note: The DTD has been embedded in the DOCTYPE, rather than being in a separate file


Defining Attributes

• <!ATTLIST element attrName type modifier>• Example

<!ELEMENT Customer (#PCDATA)><!ATTLIST Customer id CDATA #IMPLIED>

<!ELEMENT Product (#PCDATA)><!ATTLIST Product

cost CDATA #FIXED “200” id CDATA #REQUIRED>


Attribute Types

• CDATA– Essentially anything; simply unparsed data<!ATTLIST Customer id CDATA #IMPLIED>

• Enumeration– Attribute(value1|value2|value3)[Modifier]

• Eight other attribute types– ID,IDREF,NMTOKEN,NMTOKENS,ENTITY,ENTITIES,NOTATION


Attribute Modifiers

• #IMPLIED– Attribute is not required<!ATTLIST Customer id CDATA #IMPLIED>

• #REQUIRED– Attribute must be present<!ATTLIST Customer id CDATA #required>

• #FIXED “value”– Attribute is present and always has this value<!ATTLIST Customer id CDATA #FIXED “EN”>

• Default value (applies to enumeration)<!ATTLIST car colour (red | white | blue) “white”>


XML DOCTYPE

• Document Type Declarations– Specifies the location of the DTD defining the syntax and structure

of elements in the document

– Common forms• <!DOCTYPE root [DTD]>• <!DOCTYPE root SYSTEM URL>• <!DOCTYPE root PUBLIC FPI-identifier URL]>

– The root identifies the starting element (root element) of the document

– The DTD can be external to the XML document, referenced by a SYSTEM or PUBLIC URL

• SYSTEM URL refers to a private DTD– Located on the local file system or HTTP server

• PUBLIC URL refers to a DTD intended for public use


XML DOCTYPE

• Specifying a PUBLIC DTD

<!DOCTYPE root PUBLIC FPI-identifier URL>– The Formal Public identifier (FPI) has four parts:

1. Connection of DTD to a formal standard

2. Group responsible for the DTD

3. Description and type of document

4. Language used in the DTD

– Examples:

<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN”

http://www.w3.org/TR/html4/strict.dtd>

<!DOCTYPE XmlStudents SYSTEM "Student.dtd">

XML Comments

• The same as HTML comments


Processing Instructions

• Application-specific instruction to the XML processor– <?processor:instruction?>

• Example<?xml version="1.0" encoding="UTF-8"?><?xml:stylesheet type="text/xsl" href="list.xsl"?><!DOCTYPE XmlStudents SYSTEM "Student.dtd"><XmlStudents> <XmlStudent>



XML Root Element

• Required for XML-aware applications to recognise beginning and end of document

• Example<?xml version="1.0" encoding="UTF-8"?><?xml:stylesheet type = "text/xsl" href = "list.xsl"?><!DOCTYPE XmlStudents SYSTEM "Student.dtd"><XmlStudents> <XmlStudent>



XML Tags

• Tag names;– Case sensitive– Start with a letter or underscore– After first character, numbers, ‘-’ and ‘.’ are allowed– Cannot contain whitespaces– Avoid use of colon except for indicating namespaces

• For a well-formed XML document– Every tag must have an end tag

• <element1>…..</element1>• <element2/>

– All tags must be nested (tag order can’t be mixed)

• Tags can also have attributes<img src="harry.gif"></img>

– Attributes provide metadata for the element– Every attribute value must be enclosed in ”” with no commas

between attributes– Same naming convention as elements

Document Entities

• Entities refer to data item, typically text– General entity references start with & and end with ;– The entity reference is replaced by its true value when parsed– The characters < > & ’ “ require entity references to avoid conflicts with

the XML application (parser)< > & ' "

• Entities are user definable<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE university[<!ELEMENT university (faculty)><!ENTITY myfaculty "Faculty of Computing Engineering and Technology">]><university> <faculty>My Faculty is,&myfaculty;</faculty></university>

• Note we’ve included the DTD in the prolog of the above code


Document Entities

• Internet Explorer displays:

CDATA Sections

• CDATA (character data) is not parsed• Example

<?xml version = "1.0"?><book title = "C++ How to Program" edition = "3"> <sample> // C++ comment if ( this->getX() < 5 && value[ 0 ] != 3 ) cerr << this->displayError(); </sample> <sample> <![CDATA[ // C++ comment if ( this->getX() < 5 && value[ 0 ] != 3 ) cerr << this->displayError(); ]]> </sample> C++ How to Program by Deitel & Deitel</book>


CDATA Sections

• Internet Explorer displays


Extensible Stylesheet Language (XSL)

• Consists of two parts – XSL Transformation language (XLST)

• Used to transform an XML document from one form to another

– XSL formatting objects• Provides an alternative to CSS for formatting and styling an XML

document

• More information– XML: http://www.w3schools.com/xml/default.asp

– DTD: http://www.w3schools.com/dtd/default.asp

– XSLT: http://www.w3schools.com/xsl/default.asp