Chapter 20 Extensible Markup Language XML

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Chapter 20 Extensible Markup Language (XML)
Outline 20.1 Introduction 20.2 Structuring
Data 20.3 XML Namespaces 20.4 Document Type
Definitions (DTDs) and Schemas 20.4.1 Document
Type Definitions 20.4.2 W3C XML Schema Documents
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Objectives

• In this lesson, you will learn
• To understand XML.
• To be able to mark up data using XML.
• To become familiar with the types of markup
  languages created with XML.
• To understand the relationships among DTDs,
  Schemas and XML.
• To understand the fundamentals of DOM-based and
  SAX-based parsing.
• To understand the concept of an XML namespace.
• To be able to create simple XSL documents.
• To become familiar with Web services and related
  technologies.

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20.1  Introduction

• XML stands for EXtensible Markup Language.
• XML is designed to describe data and to focus on
  what data is.
• You will learn
• About XML
• The difference between XML and HTML
• How to start using XML in your applications.

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20.1  Introduction

• What is XML?
• XML stands for EXtensible Markup Language
• XML is a markup language much like HTML
• XML was designed to describe data
• XML tags are not predefined. You must define 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
• XML is a W3C Recommendation

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20.1  Introduction

• The Main Difference Between XML and HTML
• XML was designed to carry data.
• XML is not a replacement for HTML.
• 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.

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20.1  Introduction

• XML Does not DO Anything
• XML was not designed to DO anything.
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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20.1  Introduction

• XML is Free and Extensible
• XML tags are not predefined. You must "invent"
  your own tags.
• XML is a Complement to HTML
• XML is not a replacement for HTML.
• XML in Future Web Development
• XML is going to be everywhere.

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20.1  Introduction

• How can XML be Used?
• XML can Separate Data from HTML
• XML is Used to Exchange Data
• XML Can be Used to Share Data
• XML Can be Used to Store Data
• XML Can be Used to Create New Languages

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20.1  Introduction

• The syntax rules of XML are very simple and very
  strict. The rules are very easy to learn, and
  very easy to use.
• Because of this, creating software that can read
  and manipulate XML is very easy.

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article.xml(1 of 1)
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20.2  Structuring Data

• All XML Elements Must Have a Closing Tag
• XML Tags are Case Sensitive
• XML Elements Must be Properly Nested
• XML Documents Must Have Only One Root Element
• XML Attribute Values Must be Quoted
• Comments in XML is the same as XHTML

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20.2  Structuring Data

• Again from the example, XML document has
• XML declaration
• Value version
• Indicates the XML version to which the document
  conforms
• Root element
• Element that encompasses every other elements
• Container element
• Any element contains other elements
• Child elements
• Elements inside a container element
• Empty element flag
• Does not contain any text

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letter.xml(1 of 2)
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letter.xml(2 of 2)
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20.2  Structuring Data

• Use of Elements vs. Attributes?!
• Data can be stored in child elements or in
  attributes.
• ltperson sex"female"gt
• ltfirstnamegtAnnalt/firstnamegt
• ltlastnamegtSmithlt/lastnamegt
• lt/persongt
• Vs.
• ltpersongt
• ltsexgtfemalelt/sexgt
• ltfirstnamegtAnnalt/firstnamegt
• ltlastnamegtSmithlt/lastnamegt
• lt/persongt
• Which one to use?

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20.2  Structuring Data

• The following is valid, but do not do it (this is
  not what XML is for)
• ltnote day"12" month"11" year"2002"
• to"Tove" from"Jani" heading"Reminder"
• body"Don't forget me this weekend!"gt
• lt/notegt
• Do it in case of id
• ltmessagesgt
• ltnote id"p501"gt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt
• ltnote id"p502"gt
• lttogtJanilt/togt
• ltfromgtTovelt/fromgt
• ltheadinggtRe Reminderlt/headinggt
• ltbodygtI will not!lt/bodygt

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20.3  XML Namespaces

• Since element names in XML are not predefined, a
  name conflict will occur when two different
  documents use the same element names.
• This XML document carries information in a table
• lttablegt
• lttrgt
• lttdgtAppleslt/tdgt
• lttdgtBananaslt/tdgt
• lt/trgt
• lt/tablegt
• This XML document carries information about a
  table (a piece of furniture)
• lttablegt
• ltnamegtAfrican Coffee Tablelt/namegt
• ltwidthgt80lt/widthgt
• ltlengthgt120lt/lengthgt
• lt/tablegt

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20.3  XML Namespaces

• Solving Name Conflicts Using a Prefix
• This XML document carries information in a table
• lthtablegt
• lthtrgt
• lthtdgtAppleslt/htdgt
• lthtdgtBananaslt/htdgt
• lt/htrgt
• lt/htablegt
• This XML document carries information about a
  piece of furniture
• ltftablegt
• ltfnamegtAfrican Coffee Tablelt/fnamegt
• ltfwidthgt80lt/fwidthgt
• ltflengthgt120lt/flengthgt
• lt/ftablegt

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20.3  XML Namespaces

• Solving Name Conflicts Using Namespaces
• The XML Namespace (xmlns) Attribute
• The XML namespace attribute is placed in the
  start tag of an element and has the following
  syntax
• xmlnsnamespace-prefix"namespaceURI"

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namespace.xml(1 of 1)
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20.3  XML Namespaces

• Default Namespaces
• Defining a default namespace for an element saves
  us from using prefixes in all the child elements.
  It has the following syntax
• xmlns"namespaceURI"

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20.4  Document Type Definitions (DTDs) and
Schemas

• Two types of documents for specifying XML
  document structure
• Document Type Definition (DTDs)
• Schemas

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20.4.1 Document Type Definitions

• The purpose of a DTD (Document Type Definition)
  is to define the legal building blocks of an XML
  document.
• It defines the document structure with a list of
  legal elements and attributes.
• A DTD can be declared inline inside an XML
  document, or as an external reference.

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20.4.1 Document Type Definitions

• External DTD Declaration
• If the DTD is declared in an external file, it
  should be wrapped in a DOCTYPE definition with
  the following syntax
• lt!DOCTYPE root-element SYSTEM "filename"gt
• For Example
• lt?xml version"1.0"?gt
• lt!DOCTYPE note SYSTEM "note.dtd"gt
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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20.4.1 Document Type Definitions

• "note.dtd" contains
• lt!ELEMENT note (to,from,heading,body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt

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20.4.1 Document Type Definitions

• Why Use a DTD?
• Each of your XML files can carry a description of
  its own format.
• Independent groups of people can agree to use a
  standard DTD for interchanging data.
• Your application can use a standard DTD to verify
  that the data you receive from the outside world
  is valid.
• You can also use a DTD to verify your own data.

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20.4.1 Document Type Definitions

• The Building Blocks of XML Documents
• ELEMENT type declaration
• Defines rules
• ATTLIST attribute-list declaration
• Defines an attribute

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20.4.2 W3C XML Schema Documents

• XML Schema is an XML-based alternative to DTDs.
• An XML Schema describes the structure of an XML
  document.
• The XML Schema language is also referred to as
  XML Schema Definition (XSD).

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20.4.2 W3C XML Schema Documents

• XML File
• lt?xml version"1.0"?gt
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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20.4.2 W3C XML Schema Documents

• DTD File
• lt!ELEMENT note (to, from, heading, body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt

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20.4.2 W3C XML Schema Documents

• XML Schema
• lt?xml version"1.0"?gt
• ltxsschema xmlnsxs"http//www.w3.org/2001/XMLSch
  ema"
• targetNamespace"http//www.w3schools.com"
• xmlns"http//www.w3schools.com"
• elementFormDefault"qualified"gt
• ltxselement name"note"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"to" type"xsstring"/gt
• ltxselement name"from" type"xsstring"/gt
• ltxselement name"heading" type"xsstring"/gt
• ltxselement name"body" type"xsstring"/gt
• lt/xssequencegt
• lt/xscomplexTypegt
• lt/xselementgt
• lt/xsschemagt

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20.4.2 W3C XML Schema Documents

• Root element schema
• Contains elements that define the XML document
  structure
• targetNamespace
• Namespace of XML vocabulary the schema defines
• element tag
• Defines element to be included in XML document
  structure
• name and type attributes
• Specify elements name and data type respectively
• Built-in simple types
• date, int, double, time, etc

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20.4.2 W3C XML Schema Documents

• Two categories of data types
• Simple types
• Cannot contain attributes or child elements
• Complex types
• May contain attributes and child elements
• complexType
• Define complex type
• Simple content
• Cannot have child elements
• Complex content
• May have child elements

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book.xml(1 of 1)
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book.xsd(1 of 1)
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computer.xsd(1 of 2)
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computer.xsd(2 of 2)
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laptop.xml(1 of 1)