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XSD Attributes
All attributes are declared as simple types.
What is an Attribute?
Simple elements do not contain attributes. If
an element has attributes, then it is of a complex
type element. But the attribute itself is always
declared as a simple type.
Defining an Attribute?
The syntax for defining an attribute is:
<xs:attribute name=”aaa” type=”bbb”/>
where aaa is the name of the attribute and
bbb specifies the data type of the attribute.
XML Schema has a lot of built-in data types.The most common types are:
• xs:string
• xs:decimal
• xs:integer
• xs:Boolean
• xs:date
• xs:time
Example:
Here is an XML element with an attribute:
<name lang=”EN”>Rahul</name>
And here is the corresponding attribute
definition:
<xs:attribute name=”lang” type=”xs:string”/
>
Default Values for Attributes
Attributes may have a specified default value
OR a specified fixed value A default value is
automatically assigned to the attribute when
no other value is specified for example..the
default value is “EN”:
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<xs:attribute name=”lang” type=”xs:string”
default=”EN”/>
Fixed Values for Attributes
A fixed value is automatically assigned to the
attribute, and it cannot further specify another
value for example. The fixed value is “EN”:
<xs:attribute name=”lang” type=”xs:string”
fixed=”EN”/>
Optional and Required Attributes
Attributes are optional by default. To specify
that the attribute is required, use the “use”
attribute:
<xs:attribute name=”lang” type=”xs:string”
use=”required”/>
Restrictions on Content
When an XML element or attribute has a data
type defined, it can put restrictions on the
element’s or attribute’s content. If an XML
element is of type “xs:age” and contains a string
like “Hello”, the element will not validate. With
XML Schemas, user can also add his own
restrictions to XML elements and attributes.
These restrictions are called facets. |
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Feb 2008 | Java Jazz Up |22 |
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