Wednesday, July 24, 2013

Java WebService Tutorial - Part 05 ( XSD )


In this tutorial  we will look in detail about XSD (XmlSchemaDefinition) in details now....

XSD : 

It is used in WSDL Document to define the data types of Method takes .Such as Input Parameters data types,Output Parameter data types,attribute types and return types.

It defines element that can appear in Document.

It defines attributes that can appear in the Document.

It defines the order of Child element and define no.of child elements.

It defines whether an elemnt is empty or can include text.
 
It defines default and fixed value for elements and attributes.

It can define in the WSDL itself or it can be refer externally by importing the XSD URL in the WSDL just like JavaScript and CSS.

It's an alternative to DTD's.More Powerful then DTD.(Document Type Definition)

Multiple Schema's can refer in one WSDL.Allows re-usability.Allow Namespace.

We can define our own dataype derived from the standard types.

Root Element of XSD :
  
<schema> : This is the root element of any XML Schema Document.It can contain attribute also.

 Syntax:
<? xml version="1.0" ? >
<xs:schema>
------
------
</xs:schema>

Ex:

<?xml version="1.0"?>

<xs:schema xmlns:"http://www.w3.org/2001/XMLSchema" targetNameSpace="http://www.ayaz.com" xmlns="http://www.ayaz.com" elementFromDefault="qualified">
...............
...............

</xs:schema>

Here xs:schema  xmlns follows the namespace define the w3 standards. targetNamspace schema defines the elements defines by this schema comes from ayaz.com.elementfromDefault specifies that every element should be namespace qualified.


Simple Example : (note.xml)
------------------------------------
<?xml version="1.0"?>
<note>
<from>Tom</from>
<to>Jack</to>
<heading>Remainders</heading>
<body> Dont'forget</body>
</note>

note.xsd :  Defines element for note.xml

<?xml version="1.0"?>
<xs:schema xmlns:"http://www.w3.org/2001/XMLSchema" targetNameSpace="http://www.ayaz.com" xmlns="http://www.ayaz.com" elementFromDefault="qualified">
.
<xs:element name="note">
<xs:complexType>
<xs:sequence>
<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/>
 </xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>

We will look on each of the element in detail in later part.So i have the xsd for my xml element now i can refer in my Document .

<?xml version="1.0"?>
< note xmlns="http://www.ayaz.com" xmlns=xsi="http://www.w3org.2001/XMLSchema-instance"
xsi:schemaLocation="http://www.ayaz.com/note.xsd">
<from>Tom</from>
<to>Jack</to>
<heading>Remainders</heading>
<body> Dont'forget</body>
</note>
Red color highlighted - tells the Schema validator that all elements used in this XML Document are declared in "http://www.ayaz.com"

Blue color highlighted - tells once you have the XML Schema instances we can use the SchemaLocation Attribute.

Brown Color highlighted - tells the namespace used for the xsd and it's location.

2. XSD Elements:

 XSD elements can be classified as "Single" and Complex" Element. 

a.Simple Element :

A Simple element does not have any attribute and other elements.

It can contain only Text.The Text can be of any type (String,boolean,Int)or it can be custom type define by the user.

We can also add restrictions such as limit the content or to match the specific pattern.

Synatx: 

<xs:element name="------ " type="------"/>

Ex: <xs:element name="firstname" type="xs:String"/>

Default & Fixed Value :

Default - This value is taken when there is no value is provided.
Fixed - This value is taken assigned automatically to the element and cannot assign other values.

Ex:
<xs:element name="firstname" type="xs:String" default="John "/>

<xs:element name="color" type="xs:String" fixed="red"/>


b. XSD Attributes:

Simple elements cannot have attributes. If an element is specified with attribute then it is considered ad complex type element.But a attribute always declared as   simple type.

Synatx :

<xs:attribute name="-----" type="----"/>

Ex:

<xs:attribute name="lang" type="xs:String" />

<lastname lang="en">Smith</lastname> -- Refering in XML Document.

Note: Default and fixed behave same way as the does for simple element.

Optional & required

Attribute can be specify as optional or required one.Attributes are optional by default to make the attribute declared as required we should declared by the "use" keyword.

<xs:attribute name="lang" type="xs:String"  use="required'/>

c. XSD Restrictions /Facets   :

<xs:restriction> is used to set restrcitions.

Restriction on Simple Element

Ex: To accept values between 0-120

<xs:element name="age">
  <xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:minInclusive value="0"/>
      <xs:maxInclusive value="120"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>


To set Restrictions on set of values use the enumeration

<xs:element name="car">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="Audi"/>
      <xs:enumeration value="Golf"/>
      <xs:enumeration value="BMW"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

Length Restriction

 <xs:element name="password">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:length value="8"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>
 

Constraint          Description
enumeration Defines a list of acceptable values
fractionDigits Specifies the maximum number of decimal places allowed. Must be equal to or greater than zero
length Specifies the exact number of characters or list items allowed. Must be equal to or greater than zero
maxExclusive Specifies the upper bounds for numeric values (the value must be less than this value)
maxInclusive Specifies the upper bounds for numeric values (the value must be less than or equal to this value)
maxLength Specifies the maximum number of characters or list items allowed. Must be equal to or greater than zero
minExclusive Specifies the lower bounds for numeric values (the value must be greater than this value)
minInclusive Specifies the lower bounds for numeric values (the value must be greater than or equal to this value)
minLength Specifies the minimum number of characters or list items allowed. Must be equal to or greater than zero
pattern Defines the exact sequence of characters that are acceptable
totalDigits Specifies the exact number of digits allowed. Must be greater than zero
whiteSpace Specifies how white space (line feeds, tabs, spaces, and carriage returns) is handled

3. Complex XSD Elements :

A complex element is an XML element that contains other elements and/or attributes.
There are four kinds of complex elements:
  • empty elements
  • elements that contain only other elements
  • elements that contain only text
  • elements that contain both other elements and text.
empty element :

An empty complex element cannot have contents, only attributes.

An empty XML element

<product prodid="1345" /> 

 Ex:
<xs:element name="product">
  <xs:complexType>
    <xs:attribute name="prodid" type="xs:positiveInteger"/>
  </xs:complexType>
</xs:element> 

Element which have elements only :

An "elements-only" complex type contains an element that contains only other elements.

An XML element, "person", that contains only other elements:

<person>
  <firstname>John</firstname>
  <lastname>Smith</lastname>
</person>

You can define the "person" element in a schema, like this:
<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

Text- Only :

A complex text-only element can contain text and attributes.

This type contains only simple content (text and attributes), therefore we add a simpleContent element around the content. When using simple content, you must define an extension OR a restriction within the simpleContent element, like this:
<xs:element name="somename">
  <xs:complexType>
    <xs:simpleContent>
     
        ....
        ....
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

OR

<xs:element name="somename">
  <xs:complexType>
    <xs:simpleContent>
     
        ....
        ....
      </xs:restriction>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

Mixed Complex Elements:
A mixed complex type element can contain attributes, elements, and text.

An XML element, "letter", that contains both text and other elements:
<letter>
  Dear Mr.<name>John Smith</name>.
  Your order <orderid>1032</orderid>
  will be shipped on 2001-07-13.
</letter>
The following schema  declares the "letter" element:

  <xs:complexType mixed="true">
    <xs:sequence>
      <xs:element name="name" type="xs:string"/>
      <xs:element name="orderid" type="xs:positiveInteger"/>
      <xs:element name="shipdate" type="xs:date"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

4 . Indicators
There are seven indicators:
Order indicators:
  • All
  • Choice
  • Sequence
Occurrence indicators:
  • maxOccurs
  • minOccurs
Group indicators:
  • Group name
  • attributeGroup name

Mostly Used indicators are discussed below :

Sequence Indicator

The <sequence> indicator specifies that the child elements must appear in a specific order:
<xs:element name="person">
   <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

Occurence Indicator 

Occurrence indicators are used to define how often an element can occur.

maxOccurs Indicator
The <maxOccurs> indicator specifies the maximum number of times an element can occur:
<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="full_name" type="xs:string"/>
      <xs:element name="child_name" type="xs:string" maxOccurs="10"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>
The example above indicates that the "child_name" element can occur a minimum of one time (the default value for minOccurs is 1) and a maximum of ten times in the "person" element.

minOccurs Indicator 

 The <minOccurs> indicator specifies the minimum number of times an element can occur:
<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="full_name" type="xs:string"/>
      <xs:element name="child_name" type="xs:string"
      maxOccurs="10" minOccurs="0"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>
The example above indicates that the "child_name" element can occur a minimum of zero times and a maximum of ten times in the "person" element.

To allow an element to appear an unlimited number of times, use the maxOccurs="unbounded" statement


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