The range of X509SerialNumber

Hi,

In the xmldsig-core or RFC3275,  X509SerialNumber is defined as "integer"

<complexType name="X509IssuerSerialType"> 
     <sequence> 
       <element name="X509IssuerName" type="string"/> 
       <element name="X509SerialNumber" type="integer"/> 
     </sequence>
</complexType>

As I know, serialNumber in a certificate is a ASN1 "INTEGER", which may 
be a very large value, such as "123456789012345678901234567890", which 
can not assigned to a general "int" or "long" variable. In XML Schema 
specification, I do not find the evidence that a "integer" value can 
hold BIG INTEGER like the above example. So I think the type of 
 X509SerialNuber may be "base64Binary".

Am I right or wrong?
Andrew