使用XMLStarlet时出现命名空间错误

xml sel -t -m "Config/Application" -v "@rmiPort" -n config.xml
namespace error : Namespace prefix log4j on configuration is not defined
                    <log4j:configuration>
                                        ^

config.xml有以下声明:

<?xml version="1.0"?>
<!DOCTYPE Config SYSTEM "../../../dtds/Config.dtd">
<Config>
...
<Logger>
 <log4j:configuration>
...

config.dtd如下所示:

<?xml version="1.0" encoding="UTF-8" ?>

<!ENTITY % log4j:configuration SYSTEM "log4j.dtd">
%log4j:configuration;
...
    <!ELEMENT Logger ((log4j:configuration)*)>

知道如何修复名称空间或消除错误吗?