Add session.previous_id

CHANGELOG.md

@@ -24,6 +24,8 @@ release.
 
 ### Features
 
+- Adds `session.previous_id` to session.md
+  ([#348](https://github.com/open-telemetry/semantic-conventions/pull/348))
 - Metric namespaces SHOULD NOT be pluralized.
   ([#267](https://github.com/open-telemetry/opentelemetry-specification/pull/267))
 

docs/general/session.md

@@ -11,12 +11,17 @@ Consequently, a Session is represented as a collection of Logs, Events, and Span
 throughout the Session's duration. Each Session is assigned a unique identifier, which is included as an attribute in
 the Logs, Events, and Spans generated during the Session's lifecycle.
 
+When a session reaches end of life, typically due to user inactivity or session timeout, a new session identifier
+will be assigned. The previous session identifier may be provided by the instrumentation so that telemetry
+backends can link the two sessions.
+
 ## Attributes
 
 <!-- semconv session-id -->
 | Attribute  | Type | Description  | Examples  | Requirement Level |
 |---|---|---|---|---|
 | `session.id` | string | A unique id to identify a session. | `00112233-4455-6677-8899-aabbccddeeff` | Opt-In |
+| `session.previous_id` | string | The previous `session.id` for this user, when known. | `00112233-4455-6677-8899-aabbccddeeff` | Opt-In |
 <!-- endsemconv -->
 
 [DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/tree/v1.26.0/specification/document-status.md

model/session.yaml

@@ -9,9 +9,18 @@ groups:
       Consequently, a Session is represented as a collection of Logs, Events, and Spans emitted by the Client Application
       throughout the Session's duration. Each Session is assigned a unique identifier, which is included as an attribute in
       the Logs, Events, and Spans generated during the Session's lifecycle.
+
+      When a session reaches end of life, typically due to user inactivity or session timeout, a new session identifier
+      will be assigned. The previous session identifier may be provided by the instrumentation so that telemetry
+      backends can link the two sessions.
     attributes:
       - id: id
         type: string
         brief: "A unique id to identify a session."
         examples: "00112233-4455-6677-8899-aabbccddeeff"
         requirement_level: opt_in
+      - id: previous_id
+        type: string
+        brief: "The previous `session.id` for this user, when known."
+        examples: "00112233-4455-6677-8899-aabbccddeeff"
+        requirement_level: opt_in