Small clarification for default's service.name for exporters. (#1386)

CHANGELOG.md

@@ -52,6 +52,9 @@ Updates:
   ([#1339](https://github.com/open-telemetry/opentelemetry-specification/pull/1339))
 - Trace Exporters: Fix TODOs in Jaeger exporter spec
   ([#1374](https://github.com/open-telemetry/opentelemetry-specification/pull/1374))
+- Clarify that Jaeger/Zipkin exporters must rely on the default Resource to
+  get service.name if none was specified.
+  ([#1386](https://github.com/open-telemetry/opentelemetry-specification/pull/1386))
 
 ## v0.7.0 (11-18-2020)
 

specification/trace/sdk_exporters/jaeger.md

@@ -43,6 +43,8 @@ single process and exporters need to handle this case accordingly.
 Critically, Jaeger backend depends on `Span.Process.ServiceName` to identify the service
 that produced the spans. That field MUST be populated from the `service.name` attribute
 of the [`service` resource](../../resource/semantic_conventions/README.md#service).
+If no `service.name` is contained in a Span's Resource, that field MUST be populated from the
+[default](../../resource/sdk.md#sdk-provided-resource-attributes) `Resource`.
 
 ### InstrumentationLibrary
 

specification/trace/sdk_exporters/zipkin.md

@@ -53,7 +53,9 @@ and Zipkin.
 
 Zipkin service name MUST be set to the value of the
 [resource attribute](../../resource/semantic_conventions/README.md):
-`service.name`. In Zipkin it is important that the service name is consistent
+`service.name`. If no `service.name` is contained in a Span's Resource, it MUST be populated from the
+[default](../../resource/sdk.md#sdk-provided-resource-attributes) `Resource`.
+In Zipkin it is important that the service name is consistent
 for all spans in a local root. Otherwise service graph and aggregations would
 not work properly. OpenTelemetry doesn't provide this consistency guarantee.
 Exporter may chose to override the value for service name based on a local root
@@ -62,9 +64,6 @@ span to improve Zipkin user experience.
 *Note*, the attribute `service.namespace` must not be used for the Zipkin
 service name and should be sent as a Zipkin tag.
 
-*Note*, exporter to Zipkin MUST allow to configure the default "fall back" name
-to use as a Zipkin service name.
-
 ### SpanKind
 
 The following table lists all the `SpanKind` mappings between OpenTelemetry and