xml - lesson 3

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Working with XML Schemas

NIIT eXtensible Markup Language/Lesson 3/Slide 1 of 36

Objectives

In this lesson, you will learn to:

Declare attributes in an XML schema

Identify the need for XML namespaces

Use the components of one XML schema in another

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Problem Statement 3.D.1

The head office of CyberShoppe sends informationabout 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 thatcan be saved in the data store to ensure uniformityand consistency of information.

CyberShoppe sells two categories of products, booksand toys. The product details comprise the name ofthe product, a brief description about it, the price ofthe product, and the quantity available in stock. Theprice of the product must always be greater than zero.

In addition to these details, you also need to store thecategory and product ID.

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Task List

Identify the elements and attributes required in the

XML document.

Identify the method for declaring an attribute in an

XML schema.

Identify the mechanism to restrict the values that can

be assigned to an attribute.

Declare elements and attributes.

Create an XML document.

Validate the XML document against the schema.

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Task 1: Identify the elements and attributes

required in the XML document.

Result

The required elements are:

PRODUCTDATA

PRODUCT

PRODUCTNAME

DESCRIPTION

PRICE QUANTITY

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Task 1: Identify theXML document. (Contd.)

The required attributes are:

PRODID

CATEGORY

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Task 2: Identify the method for declaring an

attribute in an XML schema.

The attribute Element

In XSD, an attribute for a user-defined element is

declared using the attribute element.

The syntax for declaring an attribute in XSD is

given below:

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Task 2: Identify the XML schema. (Contd.)

The attribute Element (Contd.)

The attribute element contains attributes thatare used to further qualify and restrict the scope

and usage of the user-defined attribute. These

attributes are discussed below.

The name Attribute Is used to specify the name of a user-defined

attribute.

Must be used when the schema element is theparent element of the attribute element.

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The ref Attribute Is used to reference a user-defined attribute

declared in the same or any other XSD

document.

The type Attribute

Takes a value, which specifies the data type of

the user-defined attribute.

Attributes can be associated with both built-inand user-defined simple data types.

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The use Attribute

The use attribute specifies the way in which anattribute must be used in an XML document.

The values that can be assigned to the use

attribute are as follows:optional: Specifies that the use of the

attribute in the XML document is optional.

default: Specifies a default value for an

attribute. You must use the value attribute ofthe attribute element if you set the valueof the use attribute to default.

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Global Attributes

Global attributes are attributes that are declaredoutside all element declarations. For such

attributes, the schema element is the parent

element.

After declaring a global attribute, you can reusethis attribute from anywhere within the schema.

Global attributes can be associated with both

simple and complex data types.

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Task 2: Identify theXML schema. (Contd.)

Result

In order to declare the category and ProdID attributes,you should use the attribute element of XSD.

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Task 3: Identify the mechanism to restrict the

values that can be assigned to an attribute.

Result

In order to restrict values that can be assigned to anattribute, you need to declare the attribute and

associate it with a user-defined simple data type.

Next, you need to create the simple data type by

using the simpleType element of XSD.

Finally, you need to use the restriction element of XSD

within the simpleType element in order to restrict the

values that can be assigned to the elements orattributes that use the simple data type.

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Task 4: Declare elements and attributes.

Task 5: Create an XML document.

Task 6: Validate the XML document against the

schema.

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Just a Minute

In addition to storing the name of the book, first and

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

also need to store the book ID and the type of coverfor each book. The type of cover can be either hard or

soft. Declare the elements and attributes required to

store book details. The book ID can also be used in

different XML documents that store products data.Ensure that the book ID attribute is reusable.

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XML Namespaces

Introduction to XML Namespaces

A namespace is a method of preventing conflicts

between elements having same names.

In XML, a namespace is a virtual space that isassigned or recognized by a Uniform ResourceIdentifier (URI).

A URI is a string that uniquely identifies theelements and attributes from different schemas.

A namespace URI is not the same as a Web URI.It does not actually point to a resource on theInternet. It is just a unique identifier used to resolveconflicts between elements having same names.

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XML Namespaces (Contd.)

Introduction to XML Namespaces (Contd.)

You can assign any name or string as a URI. XML allows you to map a prefix to a URI. You can

think of a prefix as an alias for a namespace URI.

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Declaring Namespaces

A namespace can be declared in the XSD

document by using the xmlns keyword.

This keyword is an attribute of the schemaelement, which is declared at the beginning of thedocument.

The general form of the xmlns keyword is asfollows:

xmlns:prefix=URI

There are two kinds of namespace declarations,default and explicit.

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Explicit Declaration

Inan explicit declaration, the xmlns keyword associates a

prefix with a namespace URI, as shown in the following

example:

:

Only those elements and attributes that explicitly use this

prefix come under the scope of the specified namespace.

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Problem Statement 3.D.2

The branches of CyberShoppe purchase various

products from their suppliers. The details about all

these purchase orders are sent to the head office forreporting purposes. To ensure that the data can be

accessed, regardless of the hardware and software

used at the head office, the branches send data in an

XML format. On receiving this data, the head officeneeds to verify that all branches have specified the

required information. It also needs to verify that the

data sent by various branches is in a consistent

format.

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Task List

Identify the elements and attributes required to store

data.

Identify a mechanism for applying restrictions across

multiple documents.

Declare reusable data types.

Declare the elements and attributes to be used forstoring data.

Create an XML document.

Validate the XML document against the schema.

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Task 1: Identify the store data. (Contd.)

The attributes required to store data aboutpurchase orders are:

ORDERIDPRODID

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Task 2: Identify a mechanismdocuments.

(Contd.)

The include element can have multiple

occurrences in an XSD document. The schema element is the parent element of the

include element.

The include element allows reference to any

external schema, which is defined in the context ofthe same target namespace.

A target namespace has a reference to a URI towhich a schema belongs.

The target namespace for a schema is declaredusing the targetNamespace attribute of theschema element.

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Task 2: Identify a mechanism documents.

(Contd.)

The import element

The import element performs the same function

as the include element. However, the import

element allows you to access components from

multiple schemas that may belong to different

target namespaces.

The syntax for using the import element is given

below:

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Task 2: Identify a mechanism documents.(Contd.)

Result:

In the given scenario, you can create reusable datatypes required for storing product ID and order IDin an XML schema.

You can specify the restrictions on these data

types. Then, you can use the include orimport

elements to reference these data types in anotherschema that contains the declarations for elements

and attributes required for storing purchase orderdata.

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Task 3: Declare reusable data types.

Task 4: Declare the elements and attributes tobe used for storing data.

Task 5: Create an XML document.

Task 6: Validate the XML document against the

schema.

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Just a Minute(Contd.)

The sales details sent by various branch offices

include the product ID, transaction ID, date of

transaction, customer ID, quantity ordered, and priceper unit.

The product ID, the transaction ID, and the customer

ID are used repeatedly in a number of documents.

Create reusable data types for storing these details.Also create an XML schema that uses these data

types for storing sales details. The product ID should

contain the pattern P[0-9][0-9][0-9].

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Summary

In this lesson you learned that,

The attribute element is used to declare an

attribute in the XSD document.

The attribute element has the following attributes:

name: Specifies the name of the user-defined

attribute.

ref: Contains a reference to a global attribute.

use: Specifies whether the use of the user-defined

attribute is mandatory or optional. Also allows youto specify the default value for an attribute.

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Summary (Contd.)

type: Specifies the data type of the attribute.

value: Specifies the default or fixed value for a

user-defined attribute.

The use attribute of the attribute element can take

optional, default, fixed, or required as its value.

A global attribute is used to declare an attribute that isnot associated with any element and that can be

reused within a schema.

A namespace is used to avoid naming conflicts

between elements having same names.

W ki i h XML S h

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Summary (Contd.)

The namespace is declared using the xmlns

keyword.

You can reference a schema from another schema by

using the include element or the import element.

The include element is used to reference a schema

in which the target namespace is the same as that ofthe containing document.

The import element is used to reference a schema

in which the target namespace is different from that of

the containing schema.

xml - lesson 3

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