# Semantic conventions for session

**Status**: [Experimental][DocumentStatus]

This document defines semantic conventions to apply to client-side applications when tracking sessions.

Session is defined as the period of time encompassing all activities performed by the application and the actions
executed by the end user.

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 (see [Session Start Event](#session-start-event) below).

## Attributes

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| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`session.id`](/docs/attributes-registry/session.md) | string | A unique id to identify a session. | `00112233-4455-6677-8899-aabbccddeeff` | `Opt-In` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
| [`session.previous_id`](/docs/attributes-registry/session.md) | string | The previous `session.id` for this user, when known. | `00112233-4455-6677-8899-aabbccddeeff` | `Opt-In` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |

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## Session Events

### Session Start Event

![Experimental](https://img.shields.io/badge/-experimental-blue)

[EventName](https://github.com/open-telemetry/opentelemetry-specification/tree/v1.40.0/specification/logs/data-model.md#field-eventname) MUST be`session.start`

For instrumentation that tracks user behavior during user sessions, a `session.start` event MUST be emitted
every time a session is created. When a new session is created as a continuation of a prior session,
the `session.previous_id` SHOULD be included in the event. The values of `session.id` and `session.previous_id`
MUST be different.

When the `session.start` event contains both `session.id` and `session.previous_id` fields, the event then implies
that the previous session has ended. If the session ID in `session.previous_id` has not yet ended via explicit
`session.end` event, then the consumer SHOULD treat this continuation event as semantically equivalent to
`session.end(session.previous_id)` and `session.start(session.id)`.

| Body field                                                    | Type   | Description                                          | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability                                                        |
|---------------------------------------------------------------|--------|------------------------------------------------------|-------------------------------------------------------------------------------------------------------|------------------------------------------------------------------|
| [`session.id`](/docs/attributes-registry/session.md)          | string | The ID of the new session being started.             | `Required`                                                                                            | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
| [`session.previous_id`](/docs/attributes-registry/session.md) | string | The previous `session.id` for this user, when known. | `Conditionally Required`                                                                              | ![Experimental](https://img.shields.io/badge/-experimental-blue) |

### Session End Event

![Experimental](https://img.shields.io/badge/-experimental-blue)

[EventName](https://github.com/open-telemetry/opentelemetry-specification/tree/v1.40.0/specification/logs/data-model.md#field-eventname) MUST be `session.end`

For instrumentation that tracks user behavior during user sessions, a `session.end` event SHOULD be emitted
every time a session ends. When a session ends and continues as a new session, this event SHOULD be
emitted prior to the `session.start` event.

| Body field                                                    | Type   | Description                            | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability                                                        |
|---------------------------------------------------------------|--------|----------------------------------------|--------------------------|------------------------------------------------------------------|
| [`session.id`](/docs/attributes-registry/session.md)          | string | The ID of the new session being ended. | `Required`                                                | ![Experimental](https://img.shields.io/badge/-experimental-blue) |

[DocumentStatus]: https://opentelemetry.io/docs/specs/otel/document-status