protected Layer identifyServiceLayer(SpanLayer spanLayer) {
        if (SpanLayer.FAAS.equals(spanLayer)) {
            // function as a Service
            return Layer.FAAS;
        } else {
            return Layer.GENERAL;
        }
    }
Identify the layer of span's service/instance owner. Such as  ${@link Layer#FAAS} and ${@link Layer#GENERAL}.
oap-server/analyzer/agent-analyzer/src/main/java/org/apache/skywalking/oap/server/analyzer/provider/trace/parser/listener/CommonAnalysisListener.java