XML - Lesson 2

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Ensuring Consistency of Data in XML

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NIIT eXtensible Markup Language/Lesson 2/Slide 1 of 49

Objectives

In this lesson, you will learn to:

Declare elements and attributes in a Document TypeDefinition (DTD)

Create an XML Schema

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Problem Statement 2.D.1

The head office of CyberShoppe sends the information

about its products to the branch offices. The product

details must be stored in a consistent format at allbranches. Restrictions must be placed on the kind of

data that can be saved in the data store to ensure

uniformity and consistency of information.

The products sold by CyberShoppe are organized intotwo categories, toys and books. The product details

comprise the name of the product, a brief description

about it, the price of the product, and the quantity

available in stock. Every product is uniquely identified

by a product ID.

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Task List

Identify the elements required for storing structureddata.

Identify the attributes.

Identify the method for storing consistent data.

Identify the method for declaring elements to be usedfor storing structured data.

Identify the method for declaring attributes.

Identify the method to validate the structure of data.

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Task List (Contd.)

Declare elements and attributes.

Store data.

Validate the structure of data.

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Task 1: Identify the elements required for storing

structured data.

Result:

The elements required to store the details about

products sold at CyberShoppe are as follows:

Represents the description of each product.DESCRIPTION

Represents the quantity of each product.QUANTITY

Represents the price of each product.PRICE

Represents the name of each product.PRODUCTNAME

Represents the details (product name, description, price, and quantity) for each

product.

PRODUCT

Indicates that data specific to various products is being stored in the document.Acts as the root element for all other elements.

PRODUCTDATA

DescriptionElement

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Task 2: Identify the attributes.

Result:

In case of CyberShoppe, you need to store all detailsabout products in an XML document.

Each product needs to have a unique identification

number for easy identification of a particular product.

Therefore, PRODUCTID can be defined as anattribute of the PRODUCT element.

The category classifies a product as Book or Toy.

Therefore, CATEGORY can also be defined as an

attribute of the PRODUCT element.

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Task 2: Identify the attributes. (Contd.)

The following table specifies the attributes to be

used in the XML document that stores product

details:

Represents the category of a product, and specifies whether a

product is a TOY or BOOK.

CATEGORY

Represents a unique identification value for each product. It must

be specified for every product.

PRODUCTID

DescriptionAttribute

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Task 3: Identify the method for storingconsistent data.

Document Type Definition

A DTD defines the structure of the content of an XMLdocument, thereby allowing you to store data in aconsistent format.

XML allows you to create your own DTDs forapplications.

You can check an XML document against a DTD.

This checking process is called validation.

XML documents that conform to a DTD areconsidered valid documents.

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Task 3: Identify the method for (Contd.)

Result:

As a DTD allows you to specify the structure and typeof data elements, a DTD can be created to specify the

structure of the document.

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Task 4: Identify the method for declaring

elements to be used for storing structured data.

In DTD, elements are declared by using the following

syntax:

content-model)>

Elements can be of following types:

Empty

Unrestricted

Container

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While declaring elements in a DTD, different symbols

can be used to specify whether an element is mandatory

or optional, and whether it can occur more than once.

The following table lists the various symbols that can be

used while defining the DTD:

Either PRODUCTNAME or

DESCRIPTION.

PRODUCTNAME|

DESCRIPTION

or|

PRODUCTNAME or

DESCRIPTION must occur in

that order.

PRODUCTNAME,

DESCRIPTION

and in specific

order

,DescriptionExampleMeaningSymbol

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DESCRIPTION can occur

multiple times.

DESCRIPTION+An element must

occur at least once.There can be

multiple

occurrences.

+

Any number of

PRODUCTNAME or

DESCRIPTION elements

can be present in any order.

(PRODUCTNAME|

DESCRIPTION)*

An element can

occur zero or

multiple times.

*

DESCRIPTION need not be

present, but if it is present, itcan occur only once.

DESCRIPTION?optional, can

occur only once.

?

DescriptionExampleMeaningSymbol

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Contains regular text that represents the price of a product.Data contentPRICE

Contains regular text that represents the quantity of a product.Data contentQUANTITY

Contains regular text that represents the description of a product.Data contentDESCRIPTION

Contains regular text that represents the name of a product.Data contentPRODUCTNAME

Contains details of other products, and hence will contain other

elements like PRODUCTNAME, DESCRIPTION, PRICE, and

QUANTITY.

Element contentPRODUCT

Contains one or more PRODUCT elements.Element contentPRODUCTDATA

DescriptionContent TypeElement


As per the given scenario, the type of content for each

element is given in the following table:

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You need to use the statement for

declaring elements in a DTD.

For example, the PRODUCTNAME element used in the

CyberShoppe scenario can be declared as follows:

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Task 5: Identify the method for declaring

attributes.

The syntax for declaring attributes in a DTD is as

follows:

valuetype [attributetype][default]>

The attributename valuetype[attributetype] [default] section is

repeated as often as necessary to create multiple

attributes for any given element.

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Task 5: Identify the attribute types and (Contd.)

Result:

In the case of CyberShoppe, the attribute and their

value types will be as follows:

You need to use the statement for

declaring attributes in a DTD.

Category must be TOYS

or BOOKS.

(enumerated)#REQUIREDCATEGORY

Product ID must have a

unique value and has to

be specified for every

product.

ID#REQUIREDPRODUCTID

DescriptionValue TypeAttribute TypeAttribute

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Task 6: Identify the method to validate the

structure of data.

To validate the structure of data in an XML document

you need to use parsers.

Parsers are software programs that check the syntax

used in an XML file. There are two types of parsers.

They are:

Non-validating parsers: Check whether an XML

document is well-formed.

Validating parsers: Check for well-formedness and

validity of an XML document.

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Task 6: Identify the method to validate (Contd.)

Result:

In order to check whether the data sent by the branchesof CyberShoppe conforms to the structure specified in

the DTD, you need a validating parser.

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Task 7: Declare elements and attributes.

Internal and External DTDs

You can declare elements and attributes in a DTD. A DTD can be classified into two types. They are:

Internal DTD

External DTD

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Task 7: Declare elements and attributes. (Contd.)

Differences between internal and external DTDs are

given in the following table:

This DTD can be used across multiple

documents.

This DTD can be used only by the document

in which it is created and cannot be usedacross multiple documents.

This DTD is maintained as a separate file. A

reference to this file in included in the XML

document.

This DTD is a part of the XML document.

External DTDInternal DTD

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To ensure that the structure of an XML document

conforms to the DTD, you must associate the DTD

with the XML document.

The declaration is used to define the

internal DTD. It can also be used to reference an

external DTD.

The syntax for defining an internal DTD in an XML

document is as follows:

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The syntax for referencing an external DTD in the

XML document is as follows:

Action:

Type the code for creating the DTD.

Save the file as products.dtd.

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E i C i t f D t i XML

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Task 9: Validate the structure of data.

Action:

Open index.htm in Internet Explorer.

Click the DTD Validator link.

Type the name of the XML document that you want to

parse in the text box.

Click the Validate button.


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Just a Minute

The branches of CyberShoppe send information aboutbooks sold by them to the head office. The book detailsmust be stored in a consistent format. Restrictions must

be placed on kind of data that can be saved in the datastore to ensure uniformity and consistency ofinformation. The details of the books sold byCyberShoppe consist of the name of the book, ISBN ofthe book, first and last names of the author of the book,and the price of the book. The ISBN should be uniquefor each book. In addition, you need to ensure that thebook category contains HISTORY, SCIENCE, orFICTION as its valid values. Create a DTD for declaringthe elements to be used for storing book details in anXML document.


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Introduction to XML Schemas

AnXML schema is used to define the structure of an

XML document.

Microsoft has developed a language that is used to

define the schema of an XML document. This

language is called the XML Schema Definition (XSD)

language.


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Advantages of XML Schemas over DTDs

Some of the advantages of an XML schema created

by using XSD over DTD are as follows:

XSD provides more control over the type of data

that can be assigned to elements and attributes as

compared to DTD.

DTD does not enable you to define your owncustomized data types. XSD enables you to create

your own data types.

XSD also allows you to specify restrictions on data.


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Advantages of XML Schemas over DTDs (Contd.)

The syntax for defining a DTD is different from thesyntax used for creating an XML document.However, the syntax for defining an XSD is thesame as the syntax of the XML document.


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Problem Statement 2.D.2The head office of CyberShoppe sends information about

its products to its branch offices. The product details must

be stored in a consistent format. Restrictions must be

placed on the kind of data that can be saved in the data

store to ensure uniformity and consistency of information.

The product details comprise the name of the product, a

brief description about it, the price of the product, and thequantity available in stock. The price of the product must

always be greater than zero.


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Task List

Identify the elements required to store data.

Identify the data type of the contents of an element.

Identify the method for declaring a simple type

element.

Identify the method for declaring a complex type

element.

Create the XML schema.

Create an XML document conforming to the schema.

Validate an XML document against the schema.


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Task 1: Identify the elements required to store

data.

Result:

As per the problem, the elements required in the XML

document are:

Represents the quantity of each product.QUANTITY

Represents the price of each productPRICE

Represents the description of each product.DESCRIPTION

Represents the name of each product.PRODUCTNAME

Represents the details (product name, description, price, and quantity)

for each product.

PRODUCT

This element indicates that data specific to various products is being

stored in the document. Therefore, it contains more elements and acts

as the root element

PRODUCTDATA

DescriptionElement


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Task 2: Identify the data type of the contents of anelement.

Every element declared in XSD, must be associatedwith a data type.

XSD provides a list of pre-defined data types.

Primitives Data Types: Fundamental data types ofXSD, such as string, decimal, float, and boolean.

Derived Data Types: Defined by using other datatypes.

Atomic Data Types: Data types that cannot bebroken further.

List Data Types: Contain a set of values.

Union Data Types: Derived from list and atomic datatypes.


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Task 2: Identify the data type of the (Contd.)

XSD also allows definition of custom data types. These

custom data types can be classified as follows:

Simple data type: A data type that contains only

values.

Complex data type: A data type that contains child

elements, attributes, and also the mixed content.


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Task 2: Identify the data type of the (Contd.)

Result:

The data type for the contents of the elements will be:

A simple type element that contains values of string data type.StringDESCRIPTION

A simple type element that contains values of positiveInteger

data type (product price must be greater than zero.

PositiveintegerPRICE

A simple type element that contains values of integer data type.IntegerQUANTITY

A simple type element that contains values of data string type.StringPRODUCTNAME

A complex type element that can hold other elements, attributes,

and mixed content. This element will hold a complex data type,

which will be defined in the later session.

Complex data typePRODUCT

A complex type element that can hold other elements, attributes,

and mixed content. This element will hold a complex data type,

which will be defined in the later session.

Complex data typePRODUCTDATA

DescriptionData TypeElement


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Task 3: Identify the method for declaring a

simple type element.

A simple element does not contain any child elements

or attributes. Simple elements contain only valuessuch as numbers, strings, and dates.

The syntax for declaring elements with a simple data

type is as follows:


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simple type element. (Contd.)

You can associate an element with a user-defined

simple data type. To do so, you must define the newsimple data type.

You can use the simpleType element of XSD to create

a user-defined simple data type.


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Task 3: Identify the method for declaring asimple type element. (Contd.)

Result:

As per the problem, the simple elements can bedeclared in the XSD as follows:


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complex type element.

A complex type element is one that contains othermarkup elements, attributes, and mixed content.

To declare a complex type element, you need to firstdefine a complex data type. After you define acomplex data type, you can declare a complexelement by associating this data type with theelement.

You can define a complex data type by using thesyntax given below:

Content model declaration


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complex type element. (Contd.)

To declare an element as a complex type element, the

element must be associated with a complex data type.

For example, to declare the element PRODUCT as a

complex type element you can associate this element

with the prdt data type as shown below:

Result

In the CyberShoppe scenario, you require two complex

type elements, PRODUCTDATA and PRODUCT.


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complex type element. (Contd.)

You can create complex type elements by associating

them with complex data types.

You can use the element element of XSD to declare a

complex type element.

You can use the complexType element of XSD tocreate the complex data type.


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Task 5: Create the XML Schema.

The Schema element

The integration of the various components of the

XSD is done using the schema element.

The declaration of an XML schema starts with the

element.

The element uses the xmlns attribute tospecify the namespace associated with the

document.

Action:

Type the XML Schema in Notepad.

Save the file as product.xsd.


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Task 6: Create an XML document conforming to

the schema.

To create a data structure that conforms to the XML

schema, you should create an XML document andassociate it with the XML schema.

An XML file cannot be directly associated with the

XML schema file. The XML file can be associated with

the XML schema only through a validator.

Action:

Type the code in Notepad.

Save the file as products.xml


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Task 7: Validate an XML document against the

schema.

Action:

Open index.htm.

Click the Schema Validator link.

Type the name of the XML document and the XSD

file.

Click the Validate button.


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Problem Statement 2.P.2The details of the books sold by CyberShoppe consist

of the name of the book, the ISBN of the book, the first

and last names of the author of the book, and the

price of the book. The ISBN must start with the letter Iand be followed by three digits.

This data must be validated to ensure that it conforms

to the standards specified in order to maintain dataintegrity. Also, the data types used for the data must

be compatible with those used in databases. All data

must be stored in a consistent format.


D t

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Summary

In this lesson, you learned that:

Document type Definition (DTD) is method for defining

the structure of the data in an XML document.

There are two types of DTD:

Internal DTD: It can be included as a part of the

document.

External DTD: it is stored as a separate file having

the declaration of all elements and attributes that

can be used in an XML document.

There are three types of elements: empty,unrestricted, and container.


D t

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Summary (Contd.) The statement is used to declare an

element in a DTD.

The statement is used to declare a list ofattributes for an element in a DTD.

The

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Summary (Contd.) Schema can be used to specify the list of elements

and the order in which these elements must appear inthe XML document.

The language that is used to describe the structure ofthe elements in a schema is called the XML SchemaDefinition (XSD) language .

The data types supported by schema are of the

following types: Primitive

Derived

Atomic

List


Doc ments

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Summary (Contd.) The simpleType element of XSD allows you to create

user-defined simple data types.

The complexType element of XSD allows you tocreate complex data types.

The restriction element can be used to specifyconstraints on values that can be stored in elementsand attributes.