Introduction to XML

1
Introduction to XML

• Updated by
• Dr Suthikshn Kumar
• Suthikshn.kumar_at_pes.edu

2
Contents

• Introduction
• Syntax of XML
• XML Document Structure
• NameSpaces
• XML Schemas
• Displaying Raw XML documents
• Displaying XML Documents with CSS
• XSLT Style Sheets
• XML Processors
• Web Services
• Summary

3
Intro to XML

• The Extensible Markup Language (XML) is a
  general-purpose markup language.
• It is classified as an extensible language
  because it allows its users to define their own
  tags.
• Its primary purpose is to facilitate the sharing
  of structured data across different information
  systems, particularly via the Internet.
• It is used both to encode documents and serialize
  data.
• In the latter context, it is comparable with
  other text-based serialization languages such as
  JSON and YAML.
• It started as a simplified subset of the Standard
  Generalized Markup Language (SGML), and is
  designed to be relatively human-legible.
• By adding semantic constraints, application
  languages can be implemented in XML. These
  include XHTML, RSS, MathML, GraphML, Scalable
  Vector Graphics, MusicXML, and thousands of
  others.
• Moreover, XML is sometimes used as the
  specification language for such application
  languages.
• XML is recommended by the World Wide Web
  Consortium. It is a fee-free open standard. The
  W3C recommendation specifies both the lexical
  grammar, and the requirements for parsing.

4
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
• XML is a W3C Recommendation
• The Extensible Markup Language (XML) became a W3C
  Recommendation 10. February 1998.

5
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.
• XML Does not DO Anything
• XML was not designed to DO anything.
• Maybe it is a little hard to understand, but XML
  does not DO anything. XML was created to
  structure, store and to send information.
• The following example is a note to Tove from
  Jani, stored as XML
• Tove Jani
  Reminder Don't forget me
  this weekend!
• The note has a header and a message body. It also
  has sender and receiver information. But still,
  this XML document does not DO anything. It is
  just pure information wrapped in XML tags.
  Someone must write a piece of software to send,
  receive or display it.
• 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 (like , ,
  etc.).
• XML allows the author to define his own tags and
  his own document structure.
• The tags in the example above (like and
  ) are not defined in any XML standard.
  These tags are "invented" by the author of the
  XML document.
• and data transmission

6
XML is a Complement to HTML

• XML is not a replacement for HTML.
• It is important to understand that XML is not a
  replacement for HTML. In future Web development
  it is most likely that XML will be used to
  describe the data, while HTML will be used to
  format and display the same data.
• My best description of XML is this XML is a
  cross-platform, software and hardware independent
  tool for transmitting information.
• XML in Future Web Development
• XML is going to be everywhere.
• We have been participating in XML development
  since its creation. It has been amazing to see
  how quickly the XML standard has been developed
  and how quickly a large number of software
  vendors have adopted the standard.
• We strongly believe that XML will be as important
  to the future of the Web as HTML has been to the
  foundation of the Web and that XML will be the
  most common tool for all data manipulation

7
XML can Separate Data from HTML

• With XML, your data is stored outside your HTML.
• When HTML is used to display data, the data is
  stored inside your HTML. With XML, data can be
  stored in separate XML files. This way you can
  concentrate on using HTML for data layout and
  display, and be sure that changes in the
  underlying data will not require any changes to
  your HTML.
• XML data can also be stored inside HTML pages as
  "Data Islands". You can still concentrate on
  using HTML only for formatting and displaying the
  data.
• XML is Used to Exchange Data
• With XML, data can be exchanged between
  incompatible systems.
• In the real world, computer systems and databases
  contain data in incompatible formats. One of the
  most time-consuming challenges for developers has
  been to exchange data between such systems over
  the Internet.
• Converting the data to XML can greatly reduce
  this complexity and create data that can be read
  by many different types of applications.
• XML and B2B
• With XML, financial information can be exchanged
  over the Internet.
• Expect to see a lot about XML and B2B (Business
  To Business) in the near future.
• XML is going to be the main language for
  exchanging financial information between
  businesses over the Internet. A lot of
  interesting B2B applications are under
  development.

8
XML Can be Used to Share Data

• With XML, plain text files can be used to share
  data.
• Since XML data is stored in plain text format,
  XML provides a software- and hardware-independent
  way of sharing data.
• This makes it much easier to create data that
  different applications can work with. It also
  makes it easier to expand or upgrade a system to
  new operating systems, servers, applications, and
  new browsers. 
• XML Can be Used to Store Data
• With XML, plain text files can be used to store
  data.
• XML can also be used to store data in files or in
  databases. Applications can be written to store
  and retrieve information from the store, and
  generic applications can be used to display the
  data.
• XML Can Make your Data More Useful
• With XML, your data is available to more users.
• Since XML is independent of hardware, software
  and application, you can make your data available
  to other than only standard HTML browsers.
• Other clients and applications can access your
  XML files as data sources, like they are
  accessing databases. Your data can be made
  available to all kinds of "reading machines"
  (agents), and it is easier to make your data
  available for blind people, or people with other
  disabilities.
• XML Can be Used to Create New Languages
• XML is the mother of WAP and WML.
• The Wireless Markup Language (WML), used to
  markup Internet applications for handheld devices
  like mobile phones, is written in XML.
• If Developers Have Sense
• If they DO have sense, all future applications
  will exchange their data in XML

9
XML Syntax

• As long as only well-formedness is required, XML
  is a generic framework for storing any amount of
  text or any data whose structure can be
  represented as a tree.
• The only indispensable syntactical requirement is
  that the document has exactly one root element
  (alternatively called the document element).
• This means that the text must be enclosed between
  a root opening tag and a corresponding closing
  tag. The following is a well-formed XML document
• This is a book....
• The root element can be preceded by an optional
  XML declaration. This element states what version
  of XML is in use (normally 1.0) it may also
  contain information about character encoding and
  external dependencies.
• The specification requires that processors of XML
  support the pan-Unicode character encodings UTF-8
  and UTF-16 (UTF-32 is not mandatory). The use of
  more limited encodings, such as those based on
  ISO/IEC 8859, is acknowledged and is widely used
  and supported.
• Comments can be placed anywhere in the tree,
  including in the text if the content of the
  element is text or PCDATA
• In any meaningful application, additional markup
  is used to structure the contents of the XML
  document. The text enclosed by the root tags may
  contain an arbitrary number of XML elements. The
  basic syntax for one element is
• content

10
Example Recipe for making bread

• cook_time"3 hours"
• Basic bread
• Flournt Yeastingredient state"warm"Water
• Saltedient
• Mix all ingredients together.
• Knead thoroughly.
• Cover with a cloth, and leave for one hour
  in warm room.
• Knead again.
• Place in a bread baking tin.
• Cover with a cloth, and leave for one hour
  in warm room.
• Bake in the oven at 350 for 30
  minutes.

11
An Example XML Document

• XML documents use a self-describing and simple
  syntax.
• Tove Jani
  Reminder
• Don't forget me this weekend!
  
• The first line in the document - the XML
  declaration - defines the XML version and the
  character encoding used in the document. In this
  case the document conforms to the 1.0
  specification of XML and uses the ISO-8859-1
  (Latin-1/West European) character set.
• The next line describes the root element of the
  document (like it was saying "this document is a
  note")
• The next 4 lines describe 4 child elements
  of the root (to, from, heading, and body)
• Tove Jani
  Reminder Don't forget me
  this weekend!And finally the last line
  defines the end of the root element
• Can you detect from this example that the
  XML document contains a Note to Tove from Jani?
  Don't you agree that XML is pretty
  self-descriptive?
• All XML Elements Must Have a Closing Tag
• With XML, it is illegal to omit the closing tag.
• In HTML some elements do not have to have a
  closing tag. The following code is legal in HTML
• This is a paragraph This is another
  paragraphIn XML all elements must have a closing
  tag, like this
• This is a paragraph This is another
  paragraph Note You might have noticed from
  the previous example that the XML declaration did
  not have a closing tag. This is not an error. The
  declaration is not a part of the XML document
  itself. It is not an XML element, and it should
  not have a closing tag.

12
Problems

• Create an XML document for a library to store
  their book list. The details of the book such as
  Title, author, Publisher, Year of publication,
  Category, Reference Number should be captured by
  the XML document.
• Create an XML documents for a travel agency. The
  xml files i.e, flights.xml, hotels.xml, capture
  the data of available flights with details about
  flight no, airlines, no. of seats, destination,
  etc. The hotels.xml captures the data regarding
  the hotels, categories, rooms, tariff, address
  etc.
• An XML file is being designed to capture the data
  in white pages telephone directory. Design the
  xml to capture data such as name, phone no.,
  street, address, city, etc.
• An XML file is being used for storing the student
  information in an University. The information
  about each student i.e,, name, usn, semester,
  branch, college name, date of birth, contact
  phone, contact address are to stored in the xml.
  Design the xml.

13
XML Tags are Case Sensitive

• Unlike HTML, XML tags are case sensitive.
• With XML, the tag is different from the
  tag .
• Opening and closing tags must therefore be
  written with the same case
• This is incorrect
  This is correctXML Elements
  Must be Properly Nested
• Improper nesting of tags makes no sense to XML.
• In HTML some elements can be improperly nested
  within each other like this
• This text is bold and italicIn XML
  all elements must be properly nested within each
  other like this
• This text is bold and italicXML
  Documents Must Have a Root Element
• All XML documents must contain a single tag pair
  to define a root element.
• All other elements must be within this root
  element.
• All elements can have sub elements (child
  elements). Sub elements must be correctly nested
  within their parent element
• .....
  

14
XML Attribute Values Must be Quoted

• With XML, it is illegal to omit quotation marks
  around attribute values. 
• XML elements can have attributes in name/value
  pairs just like in HTML. In XML the attribute
  value must always be quoted. Study the two XML
  documents below. The first one is incorrect, the
  second is correct
• date12/11/2002 Tove Jani
  Tove
  Jani The error in the first
  document is that the date attribute in the note
  element is not quoted. This is correct
  date"12/11/2002". This is incorrect
  date12/11/2002.
• With XML, White Space is Preserved
• With XML, the white space in your document is not
  truncated.
• This is unlike HTML. With HTML, a sentence like
  this
• Hello              my name is Tove,
• will be displayed like this
• Hello my name is Tove,
• because HTML reduces multiple, consecutive white
  space characters to a single white space.

15
Comments in XML

• The syntax for writing comments in XML is similar
  to that of HTML.
• There is Nothing Special About XML
• There is nothing special about XML. It is just
  plain text with the addition of some XML tags
  enclosed in angle brackets.
• Software that can handle plain text can also
  handle XML. In a simple text editor, the XML tags
  will be visible and will not be handled
  specially.
• In an XML-aware application however, the XML tags
  can be handled specially. The tags may or may not
  be visible, or have a functional meaning,
  depending on the nature of the application.

16
XML Elements are Extensible

• XML documents can be extended to carry more
  information.
• Look at the following XML NOTE example
• Tove Jani
  Don't forget me this weekend!
  Let's imagine that we created an
  application that extracted the , , and
  elements from the XML document to produce
  this output
• MESSAGE To ToveFrom Jani
• Don't forget me this weekend!Imagine that the
  author of the XML document added some extra
  information to it
• 2002-08-01 Tove
  Jani Reminder
  Don't forget me this weekend!
  Should the application break or crash?
• No. The application should still be able to find
  the , , and elements in the XML
  document and produce the same output.
• XML documents are Extensible.

17
XML Elements have Relationships

• Elements are related as parents and children.
• To understand XML terminology, you have to know
  how relationships between XML elements are named,
  and how element content is described.
• Imagine that this is a description of a book
• My First XMLIntroduction to XML
• What is HTML
• What is XML
• XML Syntax
• Elements must have a closing tag
• Elements must be properly nested
• Imagine that this XML document describes the
  book
• My First XML
• Introduction to XML
• What is HTML
• What is XML
• XML Syntax
• Elements must have a closing tag

18
Elements have Content

• Elements can have different content types.
• An XML element is everything from (including) the
  element's start tag to (including) the element's
  end tag.
• An element can have element content, mixed
  content, simple content, or empty content. An
  element can also have attributes.
• In the example above, book has element content,
  because it contains other elements. Chapter has
  mixed content because it contains both text and
  other elements. Para has simple content (or text
  content) because it contains only text. Prod has
  empty content, because it carries no information.
• In the example above only the prod element has
  attributes. The attribute named id has the value
  "33-657". The attribute named media has the value
  "paper". 
• Element Naming
• XML elements must follow these 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, etc)
• Names cannot contain spaces

19
XML Attributes

• XML elements can have attributes.
• From HTML you will remember this SRC"computer.gif". The SRC attribute provides
  additional information about the IMG element.
• In HTML (and in XML) attributes provide
  additional information about elements
• Attrib
  utes often provide information that is not a part
  of the data. In the example below, the file type
  is irrelevant to the data, but important to the
  software that wants to manipulate the element
• computer.gif
• f the attribute value itself contains double
  quotes it is necessary to use single quotes, like
  in this example 
• Note
  If the attribute value itself contains single
  quotes it is necessary to use double quotes, like
  in this example 
• Use of
  Elements vs. Attributes

20
Well Formed XML Documents

• A "Well Formed" XML document has correct XML
  syntax.
• A "Well Formed" XML document is a document that
  conforms to the XML syntax rules that were
  described in the previous chapters
• XML documents must have a root element
• XML elements must have a closing tag
• XML tags are case sensitive
• XML elements must be properly nested
• XML attribute values must always be quoted
• Tove
• Jani
• Reminder
• Don't forget me this weekend!

21
XML Document Structure

• Two auxilary files
• DTD file that specifies its tag set and
  structural and syntactic rules
• Style sheet to describe how the content of the
  document is to be printed or displayed.
• An XML document consists of one or more entities
  that are logically related collections of
  information, ranging from a single char to a book
  chapter.
• Reasons for breaking a document into entities
• It is good to define a large document as a number
  of smaller parts so to make it easy to manage.
• If the same data appears in more than once place
  in the document, defining it as an entity allows
  any number of references to a single copy of
  data.
• Many documents include images. It must be
  separate entity called binary entity.

22
XML Document Structure

• When an XML processor encounters the name of a
  nonbinary entity in a document, it replaces the
  name with the value it references.
• Binary entities can be handled only by
  applications that deal with the document, such as
  browsers.
• Entity names can have any length. They must begin
  with a letter, a dash or a colon.
• A reference to entity is its name with a
  prepended ampersand and an appended semicolon. If
  apple_image is the name of an entity,
  apple_image is to reference it.
• When several predefined entities must appear near
  each other in an XML doc, their references
  clutter the content and make it difficult to
  read.
• In such cases character data section can be used.
• The content of character data section is not
  parsed by the XML so it cannot include any tags.

23
Document Type Definitions.

• A DTD is set of structural rules called
• Declarations which specify a set of elements that
  can appear in the document as well as how and
  where these elements may appear.
• Use of a DTD is related to the use of an external
  style sheet for XHTML.
• DTDs are used when the same tag set definition is
  used by collection of documents, perhaps by
  collection of users, and the collection must have
  a consistent and uniform structure.
• The purpose of DTD is to define a standard form
  for a collection of XML documents.
• This form is specified as the tag and attributes
  sets, as well as the rules that define how they
  can appear in a document.
• All documents in the collection can be tested
  against the DTD to determine whether they conform
  to the rules it describes.
• A DTD
• Internal DTD if it can be embedded in the XML doc
• External DTD if it is stored as a separate file,
  preferable

24
DTD syntax

• DTD is a sequence of declarations enclosed in the
  block of a DOCTYPE markup declaration.
• Each declaration within this block has the form
  of a markup declaration
• Four possible key words can be used
• ELEMENT used to define tags
• ATTLIST used to define tag attributes
• ENTITY used to define entities
• NOTATION used to define data type notation

25
Elements

• The declarations of a DTD have a form that is
  related to that of the rules of context free
  grammars, also known as Backus-Naur Form (BNF)
• Each element declaration in a DTD specifies the
  structure of one category of elements.
• The declaration provides the name of the element
  whose structure is being defined along with the
  specification of the structure of that element.
• elements )
• Example body)
• This element describes a tree structure
• Child element specification modifiers are
  barrowed from regular expressions. ( one or
  more occurences, zero or more occurences, ?
  zero or one occurrence ).
• Ex sibling)
• The leaf nodes of a DTD specify the data types of
  the contecnt of their parent nodes .
• PCDATA for parsable character data
• EMPTY when element has no content
• ANY when element may contain any content
• The form of the leaf element is as follows

26
Attributes

• The attributes of an element are declared
  separately from the element declarations in a DTD
• An attribute declaration must include the name of
  the element to which the attribute belongs, the
  attributes name and its type.
• The general form of an attribute declaration is
  as follows
• attribute_type default_value
• If more than one attribute is declared for a
  given element, the declarations can be combined.
• The common type for attributes is CDATA for any
  string characters
• Default values for attributes are any value,
  FIXED ( cannot be changed ), REQUIRED( every
  instance of the element specify a value),
  IMPLIED ( The value may or may not be specified
  in an element)
• cessna
• The following element is valid of this DTD
• jet

27
Entities

• Entities can be defined so that they can be
  referenced anywhere in the content of an XML
  document, in which case they are called general
  entities.
• The form of an entity declaration
• specifies the entity is a parameter entity (
  entities defined to be referenced only in markup
  declarations)
• Ex
• Any XML document that uses the DTD includes this
  declaration can specify the complete name with
  just the reference jfk

28
Sample planes.dtd

• Consider a booklet of ads for used aircraft.
• description, price?, seller, location)

29
Planes.xml

• 1977
• c
• skyhawk
• Light Blue and White
• 685 hours, full IFR
• 23,495
• skyway Aircraft
  
• Rapid city
• South Dakota

30
DTD

• Document Type Definition (DTD), defined slightly
  differently within the XML and SGML (the language
  XML was derived from) specifications, is one of
  several SGML and XML schema languages, and is
  also the term used to describe a document or
  portion thereof that is authored in the DTD
  language.
• A DTD is primarily used for the expression of a
  schema via a set of declarations that conform to
  a particular markup syntax and that describe a
  class, or type, of SGML or XML documents, in
  terms of constraints on the structure of those
  documents.
• As an expression of a schema, a DTD specifies, in
  effect, the syntax of an "application" of SGML or
  XML, such as the derivative language HTML or
  XHTML. This syntax is usually a less general form
  of the syntax of SGML or XML.
• In a DTD, the structure of a class of documents
  is described via element and attribute-list
  declarations.
• Element declarations name the allowable set of
  elements within the document, and specify whether
  and how declared elements and runs of character
  data may be contained within each element.
• Attribute-list declarations name the allowable
  set of attributes for each declared element,
  including the type of each attribute value, if
  not an explicit set of valid value(s).

31
Associating DTDs with documents

• A DTD is associated with an XML document via a
  Document Type Declaration, which is a tag that
  appears near the start of the XML document. The
  declaration establishes that the document is an
  instance of the type defined by the referenced
  DTD.
• The declarations in a DTD are divided into an
  internal subset and an external subset. The
  declarations in the internal subset are embedded
  in the Document Type Declaration in the document
  itself. The declarations in the external subset
  are located in a separate text file. The external
  subset may be referenced via a public identifier
  and/or a system identifier. Programs for reading
  documents may not be required to read the
  external subset.
• Examples
• Here is an example of a Document Type Declaration
  containing both public and system identifiers
• Transitional//EN" "http//www.w3.org/TR/xhtml1/DTD
  /xhtml1-transitional.dtd"
• Here is an example of a Document Type Declaration
  that encapsulates an internal subset consisting
  of a single entity declaration
• 
  

32
An XML DTD example

• An example of an XML file which makes use of and
  conforms to this DTD follows. It assumes the DTD
  is identifiable by the relative URI reference
  "example.dtd"
• people_list SYSTEM "example.dtd"
• Fred Bloggs 27/11/2008irthdate Male

33
DTD problems

• Create a DTD for a catalog of cars where each car
  has the child elements make, model, year, color,
  engine, number_of_doors, transmission_type and
  accessories. The engine element has the child
  elements number_of_cylinders and fuel_system(
  carburatted or fuel injected ). The accessories
  element has the attributes radio,
  air_conditioning, power_windows, power_steering
  and power_brakes, each of which is required and
  has the possible values yes and no. Entities must
  be declared for the names of popular car makes.
• Create an XML document with atleast three
  instances of the car element defined in the DTD
  of above. Process this document using the DTD and
  produce a display of the raw XML document.
• Design an XML document to store information about
  patients in a hospital. Information about
  patients must include name ( in three parts),
  social security number, age, room number, primary
  insurance company- including member id number,
  group number, phone number, and address---
  secondary insurance company ( in the same sub
  parts as for the primary insurance company),
  known medical problems, and know drug allergies.
  Both attributes and nested tags must be included.
  Make up sample data for at least four patients.
• Write a DTD for the document described above.
  With the following restrictions the name, social
  security number, age, room number, and primary
  insurance company are required. All the other
  elements are optional, as are middle names.

34
Valid XML Documents

• A "Valid" XML document also conforms to a DTD.
• A "Valid" XML document is a "Well Formed" XML
  document, which also conforms to the rules of a
  Document Type Definition (DTD)
• 
  
  Tove Jani
  Reminder Don't forget me
  this weekend! XML DTD
• A DTD defines the legal elements of an XML
  document.
• The purpose of a DTD is to define the legal
  building blocks of an XML document. It defines
  the document structure with a list of legal
  elements.
• XML Schema 
• XML Schema is an XML based alternative to DTD.
• W3C supports an alternative to DTD called XML
  Schema. A General XML Validator

35
XML Errors will Stop you

• Errors in XML documents will stop your XML
  program.
• The W3C XML specification states that a program
  should not continue to process an XML document if
  it finds an error. The reason is that XML
  software should be easy to write, and that all
  XML documents should be compatible.
• With HTML it was possible to create documents
  with lots of errors (like when you forget an end
  tag). One of the main reasons that HTML browsers
  are so big and incompatible, is that they have
  their own ways to figure out what a document
  should look like when they encounter an HTML
  error.
• With XML this should not be possible.
• Syntax-check your XML - IE Only
• To help you syntax-check your xml, we have used
  Microsoft's XML parser to create an XML
  validator.
• Paste your XML in the text area below, and
  syntax-check it by pressing the "Validate"
  button.
• Syntax-check your XML File - IE Only
• You can also syntax-check your XML file by typing
  the URL of your file into the input field below,
  and then press the "Validate" button
• FilenameIf you want to syntax-check an
  error-free XML file, you can paste the following
  address into the filename field
  http//www.w3schools.com/xml/cd_catalog.xml
• Note If you get the error "Access denied" when
  accessing this file, it is because your Internet
  Explorer security settings do not allow access
  across domains!

36
Namespaces

• It is often convenient to construct XML documents
  that include tag sets that are defined for and
  used by other documents.
• When a tag set is available and appropriate, it
  is better to use it than to reinvent a new
  collection of element types.
• An XML Namespace is a collection of element names
  used in XML documents.
• The name os a namespace usually has the form of a
  Uniform Resource Identifier (URI)
• A namespace for the elements of the hierarchy
  rooted at a particular element is declared as the
  value of the attribute xmlns.
• Ex /species
• Within the birds element, including all of its
  children elements, the names from the namespace
  must be prefixed with bd, as

37
Example for NameSpace usage

• Xmlns http//www.states-info.org/states
• Xmlnscap http//www.states-info.org/state-capi
  tals
• south Dakota
• 754844
• Pierre
• 12429

38
XML Schemas

• DTDs have several disadvantages
• DTDs are written in a syntax unrelated to XML, so
  they cannot be analyzed with an XML processor.
• It can be confusing to deal with two different
  syntactic forms, one to define a document and one
  to define its structure.
• DTDs do not allow restrictions on the form of
  data that can be content of a particular tag.
• XML Schema by W3C is one of the alternatives for
  DTD.
• XML Schema is an XML document, so it can be
  parsed with an XML parser.
• It also provides far more control over data types
  than do DTDs.
• Data in a specific element can be required to be
  of any one of 44 different data types.
• The user can even define new types with
  constraints on existing data types.
• To promote the transition from DTDs to XML
  schemas, XML schema was designed to allow any DTD
  to be automatically converted to an equivalent
  XML schema.

39
Schema Fundas

• Schemas can conveniently be related to the idea
  of a class and an object in an object-oriented
  programming language.
• A schema is similar to a class definition an XML
  document that conforms to the structure defined
  in the schema is similar to an object of the
  schemas class.
• XML documents that conform to a specific schema
  are considered instances of that schema.
• Schemas have primary purposes
• Schema specifies the structure of its instance
  documents, including which elements and
  attributes may appear as well as where and how
  often they may appear.
• Schema specifies data type of every element and
  attribute of its instance XML documents. ( this
  is where schemas outshine DTDs).

40
Example Schema

• --
• xmlnsxsd http//www.w3.org/2001/XMLSchema
• targetNamespace http/cs.uccs.edu/planeSchema
  
• xmlns http//cs.uccs.edu/planeSchema
• elementFormDefault qualified
• type xsdstring
• minOccurs 1
• maxOccurs unbounded /

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Planes.xml

• xmlns http//cs.uccs.edu/planeSchema
• xmlnsxsi http//www.w3.org/2001/XMLSchema-ins
  tance
• xsischemaLocation http//cs.uccs.edu/planeSch
  ema/planes.xsd
• Cessna
• Piper
• Beechcraft

42
Validating Instances of Schemas

• Determining whether a given XML instance document
  conforms to the schema.
• XSV XML Schema Validator from University of
  Edinburgh.
• The xsv can be used online.
• If the schema is not in the correct format, the
  validator will report that it could not find the
  specified schema.

43
Browser Support

• Mozilla Firefox
• As of version 1.0.2, Firefox has support for XML
  and XSLT (and CSS).
• Mozilla
• Mozilla includes Expat for XML parsing and has
  support to display XML CSS. Mozilla also has
  some support for Namespaces.
• Mozilla is available with an XSLT implementation.
• Netscape
• As of version 8, Netscape uses the Mozilla
  engine, and therefore it has the same XML / XSLT
  support as Mozilla.
• Opera
• As of version 9, Opera has support for XML and
  XSLT (and CSS). Version 8 supports only XML
  CSS.
• Internet Explorer
• As of version 6, Internet Explorer supports XML,
  Namespaces, CSS, XSLT, and XPath.
• Note Internet Explorer 5 also has XML support,
  but the XSL part is NOT compatible with the
  official W3C XSL Recommendation!

44
Viewing XML Files

• In Firefox and Internet Explorer
• Open the XML file (typically by clicking on a
  link) - The XML document will be displayed with
  color-coded root and child elements. A plus ()
  or minus sign (-) to the left of the elements can
  be clicked to expand or collapse the element
  structure. To view the raw XML source (without
  the and - signs), select "View Page Source" or
  "View Source" from the browser menu.
• In Netscape 6
• Open the XML file, then right-click in XML file
  and select "View Page Source". The XML document
  will then be displayed with color-coded root and
  child elements.
• In Opera 7 and 8
• In Opera 7 Open the XML file, then right-click
  in XML file and select "Frame" / "View Source".
  The XML document will be displayed as plain text.
  In Opera 8 Open the XML file, then right-click
  in XML file and select "Source". The XML document
  will be displayed as plain text.
• Look at this XML file note.xml
• Note Do not expect XML files to be formatted
  like HTML documents!
• Viewing an Invalid XML File
• If an erroneous XML file is opened, the browser
  will report the error.
• XML documents do not carry information about how
  to display the data.
• Since XML tags are "invented" by the author of
  the XML document, browsers do not know if a tag
  like describes an HTML table or a dining
  table.
• Without any information about how to display the
  data, most browsers will just display the XML
  document as it is.

45
Displaying XML documents with CSS

• CSS file that has style info for the elements in
  XML doc can be developed
• The other way is to use th XSLT style sheet
  technology
• XSLT provides far more power over the appearance
  of the documents display.
• XSLT is not supported by all the browsers.
• The form of a css style sheet for an XML document
  is simple.
• It is just the list element names, each followed
  by a brace-delimited set of elements CSS
  attributes.
• Planes.css
• Ad display block margin-top 15px color
  blue
• Year, make, model color red font-size 16pt
• Using in an XML
• planes.css

46
Displaying your XML Files with CSS?

• It is possible to use CSS to format an XML
  document.
• Below is an example of how to use a CSS style
  sheet to format an XML document
• Take a look at this XML file The CD catalog
• Then look at this style sheet The CSS file
• Finally, view The CD catalog formatted with the
  CSS file
• Below is a fraction of the XML file. The second
  line, href"cd_catalog.css"?, links the XML file to
  the CSS file
• href"cd_catalog.css"?
• Empire Burlesque
• Bob Dylan
• USA
• Columbia
• 10.90
• 1985
• Hide your heart
• Bonnie Tyler
• UK
• CBS Records

47
Displaying XML with XSL

• XSL is the preferred style sheet language of XML.
• XSL (the eXtensible Stylesheet Language) is far
  more sophisticated than CSS. One way to use XSL
  is to transform XML into HTML before it is
  displayed by the browser as demonstrated in these
  examples
• Below is a fraction of the XML file. The second
  line, href"simple.xsl"?, links the XML file to the
  XSL file
• href"simple.xsl"?
• Belgian Waffles
• 5.95
• two of our famous Belgian Waffles
  650

48
XML Data Embedded in HTML

• An XML data island is XML data embedded into an
  HTML page.
• Tove Jani
  Reminder Don't forget me
  this weekend!
• Then, in an HTML document, you can embed the XML
  file above with the tag. The id attribute
  of the tag defines an ID for the data
  island, and the src attribute points to the XML
  file to embed
• /body
• However, the embedded XML data is, up to this
  point, not visible for the user.
• The next step is to format and display the data
  in the data island by binding it to HTML
  elements.
• Bind Data Island to HTML Elements
• In the next example, we will embed an XML file
  called "cd_catalog.xml" into an HTML file.
• View "cd_catalog.xml".
• The HTML file looks like this
• 
  datafld"TITLE"
  
• Example explained
• The datasrc attribute of the tag binds
  the HTML table element to the XML data island.
  The datasrc attribute refers to the id attribute
  of the data island.
• tags cannot be bound to data, so we are
  using tags. The tag allows the
  datafld attribute to refer to the XML element to
  be displayed. In this case, it is
  datafld"ARTIST" for the element and
  datafld"TITLE" for the element in the
  XML file. As the XML is read, additional rows are
  created for each element

49
Example XML News

• XMLNews is a specification for exchanging news
  and other information.
• Using such a standard makes it easier for both
  news producers and news consumers to produce,
  receive, and archive any kind of news information
  across different hardware, software, and
  programming languages.
• An example XMLNews document
• Colombia Earthquake
  
• 143 Dead in Colombia Earthquake
  By Jared Kotler,
  Associated Press Writer
• Bogota, Colombia
• Monday January 25 1999 728 ET
  

50
Parsing XML Documents

• To manipulate an XML document, you need an XML
  parser.
• The parser loads the document into your
  computer's memory.
• Once the document is loaded, its data can be
  manipulated using the DOM.
• The DOM treats the XML document as a tree.
• .
• Microsoft's XML Parser
• Microsoft's XML parser is a COM component that
  comes with Internet Explorer 5 and higher.
• Once you have installed Internet Explorer, the
  parser is available to scripts.
• Microsoft's XML parser supports all the necessary
  functions to traverse the node tree, access the
  nodes and their attribute values, insert and
  delete nodes, and convert the node tree back to
  XML.
• To create an instance of Microsoft's XML parser,
  use the following code
• JavaScript
• var xmlDocnew ActiveXObject("Microsoft.XMLDOM")V
  BScript
• set xmlDocCreateObject("Microsoft.XMLDOM")ASP
• set xmlDocServer.CreateObject("Microsoft.XMLDOM")
  The following code fragment loads an existing XML
  document ("note.xml") into Microsoft's XML
  parser
• var xmlDocnew ActiveXObject("Microsoft.XMLDOM")
  xmlDoc.async"false" xmlDoc.load("note.xml")The
  first line of the script above creates an
  instance of the XML parser. The second line turns
  off asynchronized loading, to make sure that the
  parser will not continue execution of the script
  before the document is fully loaded. The third
  line tells the parser to load an XML document
  called "note.xml".

51
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52
XML DTD Example

• a very simple XML DTD to describe a list of
  persons is given below
• (name, birthdate?, gender?, socialsecuritynumber?)
  (PCDATA) socialsecuritynumber (PCDATA)
• Taking this line by line, it says
• people_list is a valid element name, and an
  instance of such an element contains any number
  of person elements. The denotes there can be 0
  or more person elements within the people_list
  element.
• person is a valid element name, and an instance
  of such an element contains one element named
  name, followed by one named birthdate (optional),
  then gender (also optional) and
  socialsecuritynumber (also optional). The ?
  indicates that an element is optional. The
  reference to the name element name has no ?, so a
  person element must contain a name element.
• name is a valid element name, and an instance of
  such an element contains parseable character data
  (PCDATA).
• birthdate is a valid element name, and an
  instance of such an element contains character
  data.
• gender is a valid element name, and an instance
  of such an element contains character data.
• socialsecuritynumber is a valid element name, and
  an instance of such an element contains character
  data.