When the year doesn't matter, but the month and day do, use xsd:recurringDate : recurringDate « XML Schema « XML Tutorial

1. XML Tutorial
2. XML Schema
3. recurringDate

File: Schema.xsd

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
  targetNamespace="http://www.java2s.com" 
  xmlns="http://www.java2s.com"
  elementFormDefault="qualified">

  <xs:element name="birthday" type="xs:recurringDate" />

</xs:schema>


File: Data.xml
<?xml version="1.0"?>
<birthday>--03-14</birthday>