diff -r c64e1588f428 -r bccda5688d71 src/StreamletAttributeFinder.h
--- a/src/StreamletAttributeFinder.h	Sat Jan 11 18:13:30 2020 +0100
+++ b/src/StreamletAttributeFinder.h	Sat Jan 11 19:10:01 2020 +0100
@@ -50,7 +50,7 @@
 
 protected:
 
-	virtual void writeFieldOfExistingFile(RelationalWriter* writer, const RequestedField& field) override {
+	virtual void writeFieldOfExistingFile(RelationalWriter* writer, const string_t& relationName, const RequestedField& field) override {
 		// TODO: paralelize also over records → fork multiple processes and distribute records across them; then collect results (with a lock)
 		if (field.group == RequestedField::GROUP_STREAMLET) {
 
@@ -73,7 +73,7 @@
 
 	static const string_t SCRIPT_PREFIX;
 
-	virtual vector<AttributeMetadata> toMetadata(RelationalWriter* writer, const RequestedField& field) override {
+	virtual vector<AttributeMetadata> toMetadata(RelationalWriter* writer, const string_t& relationName, const RequestedField& field) override {
 		if (field.group == RequestedField::GROUP_STREAMLET) {
 
 			if (cachedMetadata.count(field.id)) {
@@ -96,7 +96,7 @@
 				subProcess->write({StreamletMsg::WAITING_FOR_VERSION});
 				SubProcess::Message versionMessage = subProcess->read();
 				if (versionMessage.code == StreamletMsg::VERSION_ACCEPTED && versionMessage.parameters[0] == version) {
-					subProcess->write({StreamletMsg::RELATION_START});
+					subProcess->write({StreamletMsg::RELATION_START, relationName});
 					subProcess->write({StreamletMsg::INPUT_ATTRIBUTE_METADATA, L"path", L"string"});
 					for (string_t alias : field.getAliases()) subProcess->write({StreamletMsg::OUTPUT_ATTRIBUTE_ALIAS, alias});
 					for (int i = 0; i < field.options.size();) subProcess->write({StreamletMsg::OPTION, field.options[i++], field.options[i++]});