Xml session04

Extensible Markup Language
Objectives

In this session, you will learn to:
Reuse XML schema components
Create groups of elements and attributes in an XML schema

Ver. 1.0 Session 4 Slide 1 of 23

Reusing Components of a Schema

• Schemas support a high degree of reusability among other
schemas.
• Reusability among other schemas is achieved by using the
include or import elements.


The include Element

• The include element is used to include or refer to an
external schema that is located at a definite address.
• The syntax for using the include element is:
Specifies the element ID.
<include id="ID"
schemaLocation="filename Specifies the physical location of
the schema file.
"/>

• The include element can have multiple occurrences in an
XSD document.
• The schema element is the parent element of the include
element.
• The restriction on the usage of this element is that the
containing and contained schema files must belong to the
same target namespace.


The import Element

• The import element performs the same function as the
include element.
• The import element access components from multiple
schemas that may belong to different target namespaces.
• The syntax for using the import element is:
<import id="ID" Specifies the unique element ID.

namespace="namespace" Specifies a namespace URI to which the
imported schema belongs.
schemaLocation="filena
me"/> Is identical to the value used by the
include element.


Demo: Reusing XML Schema Components

Problem Statement:
The various products at CyberShoppe are purchased from their
suppliers through their branch offices. The purchase order
details are sent to the head office to generate reports. To
ensure that the data can be accessed across all hardware and
software used at the head office, the branch offices send data
in an XML format. On receiving this data, the head office needs
to verify that all branches have specified the required
information in a consistent format.
The purchase order details sent by the branch offices include
the product ID, order ID, date of the purchase order, name and
address of the supplier, quantity ordered, and price per unit.


Demo: Reusing XML Schema Components (Contd.)

Problem Statement (Contd.):
The product ID and order ID are used in a number of
documents. The product ID begins with P, followed by three
digits. Similarly, the order ID begins with O, followed by three
digits. These restrictions must be specified at a centralized
location such that they can be applied across multiple
documents.


Creating Grouped Elements and Attributes

An XML schema defines the following in an XML document:
Elements
Attributes
Child elements
Order of the child elements
Number of child elements
State of the element, whether it is empty or includes text
Data types for the elements and attributes
Default and fixed values for the elements and attributes


Creating Grouped Elements and Attributes (Contd.)

An XML schema combines related elements and attributes
into groups.
Creating grouped elements and attributes facilitates the
following tasks:
Create a reusable group of elements and attributes.
Select a single element from a group.
Specify the sequence of elements.
XSD provides the following elements to group user-defined
elements and attributes:
 sequence
 group
 choice
 all
 attributeGroup


The sequence Element

• The sequence element ensures that the elements declared
within the opening and closing tags of this element appear
in a specific order. The following code snippet shows the
usage of the sequence element:
<xsd:sequence>
<xsd:element name="FIRSTNAME"
type="xsd:string"/>
<xsd:element name="LASTNAME"
type="xsd:string"/>
<xsd:element name="DESIG"
type="xsd:string"/>
<xsd:element name="DEPARTMENT"
type="xsd:string"/>
</xsd:sequence>


The group Element

A set of elements can be grouped together by a common
name in an XML schema, and incorporated into a complex
data type.
The syntax for declaring a group element is:
<group
Specifies the maximum number
maxOccurs="nonNegativeInteg of times a group can occur in
er | unbounded“ the XML document.
minOccurs="nonNegativeInteg Specifies the minimum number
er" name="NCName" of times a group can occur in
ref="QName"> </group> the XML document.
Assigns a name for the group
element.
Refers to a group in a complex
type element


The choice Element

• In XSD, a single option can be selected from multiple
options using the choice element.
• The choice element allows only one of the elements
contained in the group to be present within the parent
element.
• The syntax for declaring a choice element is:
<choice id="ID"
maxOccurs="nonNegativeInteger|unbounded"
minOccurs="nonNegativeInteger">
</choice>


The all Element

• The all element uses the child elements in any order.
• The syntax for using the all element is:
<all maxOccurs="positiveInteger" minOccurs="0|1">
</all>


The attributeGroup Element

• The attributeGroup element enables grouping of
attributes that can be reused with different elements.
• The syntax for declaring attributeGroup element is:
<attributeGroup>
attribute1
attribute2
:
</attributeGroup>


Demo: Grouping Elements and Attributes in an XML Schema

Problem Statement:
The customer details of CyberShoppe need to be stored in a
central repository. To enable this, the computerized data needs
to be collated from the branch offices and maintained at a
central location. This data has to be made available to various
sections, such as the Accounts and the Sales sections of
various branches, irrespective of the hardware and software
platforms used. After collating the customer data, the head
office needs to verify that the complete information has been
made available and is stored in a consistent format.
Customer data includes the customer ID, first name, last name,
and contact information, such as the address and phone
number. A customer may provide residential or official contact
information.


Practice Questions

Which element enables the incorporation of data into a
complex data type?
a. sequence
b. group
c. all
d. attributeGroup

Answer:
b. group


Practice Questions

Consider the following statements:
Statement A: You can group a set of elements by a
common name and incorporate it into a complex data type
by using the group element.
Statement B: You can reuse a group of elements declared
earlier by using the ref attribute of the group element.


Practice Questions (Contd.)

Which of the following is correct about the preceding
statements?
a. Statement A is True, and Statement B is False.
b. Statement A is False, and Statement B is True.
c. Both, Statement A and Statement B, are True.
d. Both, Statement A and Statement B, are False.

Answer:


Practice Questions

Consider the following statements:
Statement A: The xsd:choice element allows only one of
the elements contained in the group to be present within the
parent element.
Statement B: You can set the value of the maxOccurs
attribute of the xsd:choice element to specify the
maximum number of times the group can occur within the
parent element.


Practice Questions (Contd.)

Which of the following is correct about the preceding
statements?
a. Statement A is True, and Statement B is False.
b. Statement A is False, and Statement B is True.
d. Both, Statement A and Statement B, are False.

Answer:


Practice Questions

• You want to create an attribute named baseprice with a
default value of 200, for the product element. The attribute
should accept integer values. Which of the following
statements will you use to declare the attribute?
a. <xsd:attribute name=“baseprice” default= 200
type=“xsd:integer”>
b. <xsd:attribute name=“baseprice”;
type=“xsd:integer”; use=“default” value=“200”>
c. <xsd:attribute name=“baseprice” default= “200”
type=“xsd:integer”>
d. <xsd:attribute element= “product” name=
“baseprice” default=“200” type= “xsd:integer”>

Answer:
c. <xsd:attribute name=”baseprice” default=”200”
type=”xsd:integer”>

Practice Questions

Which of the following statements is true about global
attributes?
a. Global attributes are declared within the content model of an
element.
b. While declaring a global attribute, you must specify whether
the attribute is optional or mandatory by using the use attribute.
c. The xsd:complexType element is the parent element for
global attributes.
d. After declaring a global attribute, you can reuse it anywhere
within the schema.

Answer:
d. After declaring a global attribute, you can reuse it anywhere
within the schema.


Summary

In this session, you learned that:
 You can refer to one schema from another by using the
include or import elements.
 The include element is used to refer to a schema in which
the target namespace is the same as that of the containing
schema document.
 The import element is used to refer to a schema in which the
target namespace is different from that of the containing
schema.
 You can group elements and attributes using the following
elements:
 sequence: Allows you to create a group of elements and specify
that all the elements within the group should appear in the same
sequence in which they are declared.


Summary (Contd.)

 group: Allows you to group a set of elements and use a common
name to refer to these elements. This group can be incorporated
into a complex data type.
 choice: Allows you to specify that only one of the specified set of
elements can be used at a time.
 all: Allows you to create a group of elements that can be used in
any sequence within the parent element.
 attributeGroup: Allows you to create a group of attributes that
can be reused in different elements.


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