Xml session02

Extensible Markup Language
Objectives

In this session, you will learn to:
Create an XML schema
Declare attributes in an XML schema
Identify the need for XML namespaces

Ver. 1.0 Session 2 Slide 1 of 36

Introducing XML Schema

An XML schema defines the list of elements and attributes
that can be used in an XML document.
An XML schema specifies the order in which the elements
appear in the XML document, and their data types.
Microsoft has developed the XML Schema Definition (XSD)
language to define the schema of an XML document.


Advantages of XML Schema Created Using XSDs

Some of the advantages of creating an XML schema by
using XSD are:
XSD provides control over the type of data that can be
assigned to elements and attributes.
XSD enables you to create your own data types.
XSD enables you to specify restrictions on data.
The syntax for defining an XSD is the same as the syntax used
for XML documents.
XML schema content models can be used to validate mixed
content.
XML schema is extensible.
XML schema is self documenting.


Support for XML Schemas in Various Parsers

Parsers that provide support for XML schemas are:
– IBM XML4J: Validates XML documents against several types
of XML schemas.
– MSXML 6.0: Enables loading of XML data from anonymous or
untrusted sources in a secured manner.


Data Types in XML Schemas

In an XML schema created using XSD, every element must
be associated with a data type.
XSD provides the following list of predefined data types:
Primitive
Derived
Atomic
List
Union


Data Types in XML Schemas (Contd.)

  Do not contain elements or attributes.
Primitive
  Contain only values.
Derived
 Atomic
 List
 Union



 Primitive
 Derived Are defined by using other data types
called base types.
 Atomic
Can be built-in or user-defined.
 List
 Union



 Primitive
 Derived
 Atomic Cannot be broken down into smaller
units.
 List
Can be primitive or derived.
 Union



 Primitive
 Derived
 Atomic
 List  Are derived data types that contain a set
of values of atomic data types.
 Union
 Elements referring to a list data type can
contain a value only from that defined
set.



 Primitive
 Derived
 Atomic
 List
 Union  Are derived from the atomic and list data
types.


Elements in XML Schemas

There are two types of elements, simple and complex that
can be defined in a schema.
Simple Element
A simple element does not contain any child elements or
attributes.
It contains only values, such as numbers, strings, and dates.
You can specify restrictions on elements by defining a new
simple data type from an existing data type using facet values.
You can also associate an element with a simple data type.

Let us look at the syntax for declaring a simple element.


Elements in XML Schemas (Contd.)

<xsd:element name= The name attribute specifies the name of
the element declared.
“element-name"
type="data type" The type attribute specifies the data
min0ccurs="nonNegativeInteger" type of the element declared.
max0ccurs="nonNegativeInteger| minOccurs specifies the minimum
unbounded"/> number of times the element can occur.
maxOccurs specifies the maximum
number of times the element can
appear.



Complex Element
A complex element contains other elements, attributes, and
mixed content.
To declare a complex element, you need to first define a
complex data type.
After defining the complex data type, you can declare a
complex element by associating this data type with the
element.

Let us look at the syntax for declaring a complex element.



<xsd:complexType name="data The complexType element is used to
type name"> declare a new complex data type.
Content model declaration The name attribute specifies the name of
</xsd:complexType> the new complex data type.
The Content model declaration
contains the declaration for the elements
and attributes that make up the content
of the complex type.


Demo: Creating an XML Schema

Problem Statement:
CyberShoppe, a toy and book store in the United States, sends
its product information from the head office to the branch
offices. The product details must be stored in a consistent
format. Restrictions must be placed on the type of data that
can be saved in the data store, in order to ensure uniformity
and consistency of information.
The product details include the product name, a brief
description, product price, and the available quantity on hand.
The price of the product must always be greater than zero.


Declaring Attributes in a Schema

Attributes in an XML schema are declared in the same way
as elements.
Declaring attributes in an XML schema facilitates the
assimilation of information for an XML document.
Attribute declarations can be defined in two ways:
– Simple type definitions: Facilitates local validation of the
attribute information.
– Global attribute declarations: Enables reuse of attributes.


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:
<attribute name="attributename"
ref="attributename"
type="datatypename" use="value" value="value">
</attribute>
• The attribute element contains attributes that are used
to further qualify and restrict the scope and usage of the
user-defined attribute.


Attribute Element (Contd.)

• The attribute element consists of the following
attributes:
name
ref
type
use



Is used to specify the name of a
attributes: user-defined attribute.
a name Must be used when the schema element
a ref is the parent element of the attribute
element.
a type
Colon (:) should not be included in the
a use value of the name attribute.



attributes:
Is used to refer to a user-defined
a name attribute declared either in the same or in
a ref any other XSD document.
a type
a use



attributes:
a name
a ref Takes a value that specifies the data
type of the user-defined attribute.
a type
a use



attributes:
a name
a ref
a type  Specifies the way in which an attribute
can be used in an XML document.
a use
 Values that can be assigned to the use
attribute are optional, default,
required, and fixed.


Global Attributes

Global attributes are declared outside all element
declarations.
Global attributes facilitate attribute reusability.
Global attributes can be associated with simple and
complex data types.
Global attributes have the schema element as the parent
element.


Restricting Attributes Values

In order to restrict values that can be assigned to an
attribute:
a Declare the attribute and associate it with a user-defined
simple data type.
a Create a simple data type by using the XSD simpleType
element.
a Use the XSD restriction element within the simpleType
element to restrict the values that can be assigned to the
elements or attributes that use the simple data type.


Demo: Declaring Attributes in an XML Schema

Problem Statement:
The Marketing Manager at CyberShoppe sends its product
information from its head office to the branch offices. The
branch offices update this file and send it back to the head
office on a routine basis. The product details must be stored in
a consistent format at all branches. Restrictions must be
placed on the type of data that can be saved in the data store,
to ensure uniformity and consistency of information.
CyberShoppe sells two categories of products, books and toys.
Product details include the product name, a brief description,
product price, and the available quantity on hand. The product
price must always be greater than zero. In addition to these
details, the data store needs to store the category and product
ID.


Introducing XML Namespaces

In XML, a namespace is a virtual space that is assigned or
recognized by a Uniform Resource Identifier (URI).
A namespace is a string that uniquely identifies the
elements and attributes from different schemas.
A namespace is a unique identifier used to resolve conflicts
between elements that have the same names.
The following guidelines ensure the uniqueness of a URI:
Using a URI that is controlled by the developer.
Using a relative URI.


Declaring Namespaces

• A namespace can be declared in an XSD document by
using the xmlns keyword.
• The general form of the xmlns keyword is:
xmlns is the name of the attribute.
xmlns:prefix="URI"
prefix is an optional namespace.

• There are two types of namespace declarations:
 Default Declaration: Declares a default namespace for a
document without specifying the prefix for a default
namespace.
 Explicit Declaration: Enables xmlns keyword to associate a
prefix with a namespace.


Practice Questions

Harry is creating an XML schema using XSD. To associate
each element, he is using a data type that specifies the type
of content that an element can hold. Harry wants to use
such data types that are defined using base data types.
Base data types can either be primitive or derived data
types. Which of the following data types should Harry use to
accomplish this task?
a. Primitive
b. Union
c. List
d. Derived
Answer:
d. Derived


Practice Questions

Which one of the following code snippets can be considered
well-formed?
a. <EMPLOYEE empid=e001>
<EMPNAME> Alice Peterson</EMPNAME>
<BASICPAY> $2000 </BASICPAY>
</EMPLOYEE>
b. <EMPLOYEE empid=“e001”>
<EMPNAME> Alice Peterson<BASICPAY> $2000
</EMPNAME>
</BASICPAY>
</EMPLOYEE>
c. <EMPLOYEE empid=“e001”>
</BASICPAY></EMPNAME>
</EMPLOYEE>


Practice Questions (Contd.)

d. <EMPLOYEE empid=“e001”>
</employee>

Answer:
c. <EMPLOYEE empid=“e001”>
</EMPLOYEE>

Practice Questions

You have been assigned the task of developing an XML
schema file for a new Web application in an organization.
The application aims to deliver financial news to its
subscribers. Financial news comprises the date, the name
of the organization, and the pertinent financial information.
What should you use to represent the financial news in the
XML schema?
a. Complex type element
b. Simple type element
c. Element
d. Attribute

Answer:
a. Complex type element


Practice Questions

Joe wants to specify a user-defined attribute in an XML
schema. He wants to use the use attribute in the XML
schema, but does not want to set the value for the attribute
in his XML document. Which of the following values of the
use attribute should Joe use in his XML schema?
a. optional
b. default
c. required
d. fixed

Answer:
a. optional


Practice Questions

• You have created a global attribute named color. Which of
the following attributes of the xsd:attribute element will
you use to access color?
a. use
b. name
c. ref
d. type

Answer:
c. ref


Summary

In this session, you learned that:
An XML schema can be used to specify the list of elements
and the order in which these elements must appear in the XML
document.
The XSD language is used to describe the structure of the
elements in a schema.
The data types supported by an XML schema can be
categorized as follows:
 Primitive
 Derived
 Atomic
 List
 The simpleType XSD element allows you to create
user-defined simple data types.
 The complexType XSD element allows you to create complex
data types.

Summary (Contd.)

 The restriction element can be used to specify constraints
on the values that can be stored in elements and attributes.
 The attribute element is used to declare an attribute in an
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. In addition, it allows you to specify the
default value for an attribute.
 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.


Summary (Contd.)

 A global attribute is used to declare an attribute that is not
associated with any element and can be reused within a
schema.
 A namespace is used to avoid naming conflicts between
elements having the same name.
 A namespace is declared using the xmlns keyword.


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