Lecture E-Commerce - Chapter 20: eXtensable Markup Language (XML) (part III)

In this chapter students will be able to: review the basics of creating an XML document, imposing structure on XML documents using document type definition DTD, strengthening the data-modeling capabilities of XML using XML Schemas.

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CSC 330 E-Commerce

Teacher

Ahmed Mumtaz Mustehsan

GM-IT CIIT Islamabad

Virtual Campus, CIIT

COMSATS Institute of Information Technology

T2-Lecture-5

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eXtensable Markup Language

(XML) Part - III

For Lecture Material/Slides Thanks to: www.w3schools.com

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Part 1:

Review The basics of creating an XML document

Part 2:

Imposing Structure on XML Documents using

Document Type Definition DTD

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Part 1:

Review The basics of creating an XML

document

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Part 1: A review of XML

An Extensible Markup Language (XML) document

describes the structure of data.

 XML and HTML have a similar syntax … both

derived from SGML

XML has no mechanism to specify the format for

presenting data to the user

An XML document resides in its own file with an

‘.xml’ extension

T2-Lecture-5 Ahmed Mumtaz Mustehsan www.w3schools.com

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Main Components of an XML Document

Elements: <hello>

Attributes: <item id=“33905”>

Entities: < (<)

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The Basic Rules

XML is case sensitive

All start tags must have end tags

Elements must be properly nested

XML declaration is the first statement

Every document must contain a root element

Attribute values must have quotation marks

Certain characters are reserved for parsing

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XML is different from HTML

HTML is a Hyper Text Markup language

◦Designed for a specific application, namely,

displaying, viewing, presenting and linking

hypertext documents

XML describes structure (organization of data)

XML is a subset of SGML (Standard Generalized SGML (Standard Generalized

Markup Language)

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An Address Book as an XML document

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Important Features of XML

No fixed set of tags

User is allowed to introduce New tags

Already defined set of tags can also be used

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Features of XML (cont’d)

XML supports internationalization through Unicode

Web services (e.g., e-commerce) require

exchanging data between various applications that run on different platforms

XML (with the support of namespaces) is the best

option for data exchange on the Web

XML is a data model

◦Similar to the semi-structured-data-model

XML has follow the concept of DTD and the more impressive XML Schema

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XML family

Limited styling of XML can be done with CSS

Document Type Definitions (DTDs) impose structure

on XML documents

XML Schemas strengthen the data-modeling

capabilities of XML

XPath is a language for accessing XML documents

XLink and XPointer support cross-references

XSLT is a language for transforming XML documents into other XML documents such as XHTML, for

viewing XML files

XQuery is a language for querying XML documents

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DTD : (Document Type Definition)

Imposing Structure on

XML Documents

using

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XML defines structure of the document

Some XML files only contain text documents with

tags that contain metadata and describe the

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Document Type Definitions

Document Type Definitions (DTDs) impose structure

on XML documents

There is some relationship between a DTD and a

schema, but it is not close hence the need for

additional “typing” systems exists

The DTD is a syntactic specification

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Document Type Definitions

A description of legal, valid data further contributes

to the interoperability and efficiency of using XML

A single DTD ensures a common format for each

XML document that references it

An application can use a standard DTD to verify

that data that it receives from the outside world is

valid

An XML document that conforms to the rules within

a DTD is said to be valid document

If the XML document does not follow the rules

contained within the DTD, a parser generates an

error

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A DTD adds syntactical requirements in addition to

the well-formed requirement

It helps in eliminating errors when creating or

editing XML documents

It clarifies the intended semantics

It simplifies the processing of XML documents

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An Example

In an address book, where can a phone number

appear?

Under <person>, under <name> or under both?

If we have to check for all possibilities, processing

takes longer and it may not be clear to whom a phone belongs to?

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Example: An Address Book

< person >

< name > Homer Simpson </ name >

< greet > Dr H Simpson </ greet >

< addr > 1234 Springwater Road </ addr >

< addr > Springfield USA, 98765 </ addr >

As many

as needed

As many address lines as needed (in order)

At most one greeting Exactly one name

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Specifying the Structure

name to specify a name element

greet? to specify an optional

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Specifying the Structure (cont’d)

So the whole structure of a person entry is

specified by

name, greet?, addr*, (tel | fax)*, email*

This is known as a regular expression

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Element Type Definition

for each element type E, a declaration of the form:

 <!ELEMENT E P>

 where P is a regular expression, i.e.,

P ::= EMPTY | ANY | #PCDATA | E’ |

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Summary of Regular Expressions

A The tag (i.e., element) A occurs

e1,e2 The expression e1 followed by e2

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The Definition of an Element Consists of Exactly One of the Following

A regular expression (as defined earlier)

EMPTY means that the element has no content

ANY means that content can be any mixture of

PCDATA and elements defined in the DTD

Mixed content which is defined as described on the

next slide :

(#PCDATA)

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The Definition of Mixed Content

Mixed content is described by a repeatable OR group

* The group can be repeated 0 or more times

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Some Example DTD Declarations

Example 1: Elements with Data

<! ELEMENT Month ( #PCDATA) > <! DTD declaration of an

element->

<! —Valid usage within XML file >

< Month > April </ Month >

< Month > This is a month </ Month >

<! —Invalid usage within XML file, Month can’t have children! >

<Month>

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have a single child element, include the element name within the

parenthesis.

<! ELEMENT House ( Address )>

<! —A house element has a single child address >

< House > <! —Valid usage within XML file >

< Address > 5 Park Road Chak Shahzad, Islamabad </ Address >

</ House >

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describes multiple children using a sequence, or a list of elements separated by commas The XML file must contain one of each

element in the specified order.

<! DTD declaration of an element >

<! ELEMENT address ( person , street , city , zip )>

<! ELEMENT person ( #PCDATA) >

<! ELEMENT street ( #PCDATA) >

<! ELEMENT city ( #PCDATA) >

<! ELEMENT zip ( #PCDATA) >

<! —Valid usage within XML file >

< address >

< person > Tariq Rasheed </ person >

< street > 9 th Eveneue </ street >

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Cautions concerning DTDs

 All element declarations begin with <! and end

with >

<! ELEMENT Address >

 The ELEMENT declaration is case sensitive

 The programmer must declare all elements within

an XML file

 Elements declared with the #PCDATA content

model can not have children

 When describing sequences, (e1,e2) the XML

document must contain exactly those elements in exactly that order

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An Address-Book XML Document with an Internal DTD

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE addressbook [

<!ELEMENT addressbook (person*)>

<!ELEMENT person

<!ELEMENT name (#PCDATA)>

<!ELEMENT greet (#PCDATA)>

<!ELEMENT address (#PCDATA)>

<!ELEMENT tel (#PCDATA)>

<!ELEMENT fax (#PCDATA)>

<!ELEMENT email (#PCDATA)>

The name of the DTD is addressbook

The syntax

of a DTD is

not XML

syntax

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The Address-Book XML Document

<name> Ahmed Mumtaz</name>

<greet> Prof. Mumtaz</greet>

<email> am@yahoo.com </email>

</person>

</addressbook>

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XML documents are similar to database files

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XML Representation of school database

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Well-Formed XML Documents

An XML document (with or without a DTD) is

well-formed if

◦Tags are syntactically correct

◦Every tag has an end tag

◦Tags are properly nested

◦There is a root tag

◦A start tag does not have two occurrences of the

same attribute

An XML document must be well formed

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Strengthen the data-modeling

capabilities of XML

Using XML Schemas

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What is an XML Schema?

The purpose of an XML Schema is to define the legal

building blocks of an XML document, just like a DTD

An 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

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XML Schemas are the Successors of DTDs

It is expected that 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 powerful than DTDs

XML Schemas are written in XML

XML Schemas support data types

XML Schemas support namespaces

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<xs:element name="to" type="xs:string"/>

<xs:element name="from" type="xs:string"/>

<xs:element name="heading" type="xs:string"/>

<xs:element name="body" type="xs:string"/>

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XML Schema

The Schema in previous example is interpreted like this:

Explanation of the Example:

 <xs:element name="note"> defines the element called "note"

 <xs:complexType> the "note" element is a complex type

 <xs:sequence> the complex type is a sequence of elements

 <xs:element name="to" type="xs:string"> the element "to" is of type string (text)

 <xs:element name="from" type="xs:string"> the element "from"

is of type string

 <xs:element name="heading" type="xs:string"> the element

"heading" is of type string

 <xs:element name="body" type="xs:string"> the element "body"

is of type string

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Why Use an XML Schema?

With XML Schema, the XML files can carry a

description of its own format

With XML Schema, independent groups of people

can agree on a standard for interchanging data

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XML Schemas use XML Syntax

Another great strength about XML Schemas is that they are written in XML:

You don't have to learn a new language

You can use your XML editor to edit your Schema

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XML Schemas Support Data Types

One of the greatest strength of XML Schemas is the support for data types:

It is easier to describe document content

It is easier to define restrictions on data

It is easier to validate the correctness of data

It is easier to convert data between different data

types

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XML Schemas Support Data Types

One of the greatest strength of XML Schemas is the support for data types:

It is easier to describe document content

It is easier to define restrictions on data

It is easier to validate the correctness of data

It is easier to convert data between different data

types

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XML Schemas Secure Data Communication

When sending data 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: "03-11-2004" will, in some countries, be

interpreted as 3.November and in other countries as 11.March

However, 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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XML Schemas are Extensible

XML Schemas are extensible, because they are written

in XML

With an extensible Schema definition you can:

Reuse your Schema in other Schemas

Create your own data types derived from the standard types

Reference multiple schemas in the same document

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Well-Formed is not Enough

A well-formed XML document is a document that

conforms to the XML syntax rules, like:

it must begin with the XML declaration

it must have one unique root element

start-tags must have matching end-tags

elements are case sensitive

all elements must be closed

all elements must be properly nested

all attribute values must be quoted

entities must be used for special characters

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The End eXtensable Markup Language

(XML) Part – III

Thank You

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