lesson3 :XSD Attributes

XSD Attributes :
XSD Attributes is used only with complex types .The declaration of attribute is like simple types. In declaration you define attribute name and type.

Example on attribute declaration:
<xs:attribute name="mydate" type="date"/>

Type can be :
- xs:boolean
- xs:date
- xs:time
- xs:string
- xs:decimal
- xs:integer


Example on attribute usage:

<xs:attribute name="mydate" type="xs:date"/>
This XSD code defines an attribute called "mydate" with a specific data type of "xs:date". xs:date is a built-in data type from the XML Schema standard. It represents a date without a time-zone. The format of the date should be in the form of "yyyy-mm-dd" where "yyyy" is the 4 digits year, "mm" is the 2 digits month and "dd" is the 2 digits day. This attribute can be added to an element in an XML document and it can only contain a date value in the format specified above.


Xml is:


The default value for attributes:


In this XSD code, the attribute "mydate" has a default value of "0-0-0000" which will be used in case the attribute is not present in the XML.
If the attribute is present in the XML but its value is not a valid date, an error will be raised. It's important to notice that this default value "0-0-0000" is not a valid date according to the format "yyyy-mm-dd". It is used as a placeholder or a way to indicate that the date is not provided or not known.


The default value is the value that the attribute takes when you don't specify any values.
Fixed value for attributes:

This XSD code <xs:attribute name="mydate" type="xs:date" fixed="0-0-0000" />, defines an attribute called "mydate" with a data type of "xs:date" and with a fixed value "0-0-0000". This means that the attribute must always have the value "0-0-0000" in the corresponding XML document, and it cannot be changed by a user or application.



Required attributes:
To ensure that the attribute will exist in the element you use required.


This XSD code defines an attribute called "mydate" with a specific data type of "xs:date" and with a use value of "required". This means that the attribute must be present in the corresponding XML document and it must contain a valid date in the format "yyyy-mm-dd". If the attribute is not present, or its value is not a valid date an error will be raised.