def isValidSiteID(field_data, all_data):
    """ validate site id in the form xxx-yyy-zzz where
    xxx is a 3 character identifier (eg: AKL)
    yyy is a 3 digit identifier (eg: 001)
    zzz is a 3 digit identifier (eg: 001)
    """
    temp = field_data
    sid = temp.split('-')
    if len(sid)!=3:
        raise validators.ValidationError("Site ID is \
        not valid")
    if len(sid[0])!=3:
        raise validators.ValidationError("Site ID is \
        not valid")
    if len(sid[1])!=3:
        raise validators.ValidationError("Site ID is \
        not valid")
    if len(sid[2])!=3:
        raise validators.ValidationError("Site ID is \
        not valid")
        
    if not(sid[0].isalpha() and sid[0].isupper()):
        raise validators.ValidationError("Site ID is \
        not valid")
    if not(sid[1].isdigit()):
        raise validators.ValidationError("Site ID is \
        not valid")
    if not(sid[2].isdigit()):
        raise validators.ValidationError("Site ID is \
        not valid")