Add/Append related artifacts to Workitem

Hi everyone,
i need to append to a workitem some related artifacts using curl rest api. i'm able to add a related artifacts using a command like this:
curl -D - -k -b $COOKIES -c $COOKIES -H "Content-Type: application/x-oslc-cm-change-request+json" -H "Accept: application/json" -X PATCH -d '{"rtc_cm:com.ibm.team.workitem.linktype.relatedartifact.relatedArtifact": {"rdf:resource":"'$BUILDPATH'","oslc_cm:label":"Included in Build: '$BUILD'"} }' $HOST/oslc/workitems/$WORKITEM/
but if i call again this api the new value override the old one.
There is a way to append the new value insted of rewrite the all "related artifacts" property.
i'm new in rtc api usage so hope this question doesn't sounds stupid :).
Thanks.
One answer

You have to first retrieve all related artifacts, then add your new ones and save them all together.
Comments

The problem is that i cant retrieve all artifacts at the same time. So i need a way to add a new one later

is there a documentation about curl api?

That is how the API works. You GET the representation of the resource, you add, modify or remove stuff, then you PUT the result. If you just put one relationship, all the existing ones are deleted.
CURL is an application, bot an API. CURL allows to use REST or HTML APIs.
http://open-services.net/bin/view/Main/CmSpecificationV2 is the API specification for the OSLC REST API.