XML Tutorial/XML Schema/month
If the day is irrelevant, you can specify just the year and month in an element of type xsd:month.
File: Schema.xsd
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.wbex.ru" xmlns="http://www.wbex.ru"
elementFormDefault="qualified">
<xs:element name="campaign_start" type="xs:month" />
</xs:schema>
File: Data.xml
<?xml version="1.0"?>
<campaign_start>1999-03</campaign_start>