XML PHP, filter out specific "type"

I'm extracting the required nodes from the api easily from the response here : http://ift.tt/1qNsj43

However, i am trying to get the target of relation type discogs from the below with no luck, any help appreciated

<relation-list target-type="url">
    <relation type-id="6578f0e9-1ace-4095-9de8-6e517ddb1ceb" type="wikipedia">
        <target id="cba6f347-45b3-4bd5-8b7f-818fa76a63b2">
            http://ift.tt/1qNu3Ky
        </target>
    </relation>
    <relation type-id="99e550f3-5ab4-3110-b5b9-fe01d970b126" type="discogs">
        <target id="e9e6e840-ca1a-47fa-b835-47d0d86bcda8">
            http://ift.tt/1r2vZfI
       </target>
    </relation>
    <relation type-id="b988d08c-5d86-4a57-9557-c83b399e3580" type="wikidata">
        <target id="f9b00d41-6f25-4174-9c72-ba1c452cfa6d">
            http://ift.tt/1qNu3KC
        </target>
    </relation>
</relation-list>