First stab at documenting the art of defining semantic conventions

CONTRIBUTING.md

@@ -14,6 +14,7 @@ requirements and recommendations.
 - [Sign the CLA](#sign-the-cla)
 - [How to Contribute](#how-to-contribute)
   - [Which semantic conventions belong in this repo](#which-semantic-conventions-belong-in-this-repo)
+  - [Suggesting conventions for a new area](#suggesting-conventions-for-a-new-area)
   - [Prerequisites](#prerequisites)
   - [1. Modify the YAML model](#1-modify-the-yaml-model)
     - [Code structure](#code-structure)
@@ -81,6 +82,18 @@ and helps to keep conventions consistent and backward compatible.
 Want to define your own conventions outside this repo while building on OTel’s?
 Come help us [decentralize semantic conventions](https://github.com/open-telemetry/weaver/issues/215).
 
+### Suggesting conventions for a new area
+
+Defining semantic conventions requires a group of people who are familiar with the domain,
+are involved with instrumentation efforts, and are committed to be the point of contact for
+pull requests, issues, and questions in this area.
+
+Check out [project management](https://github.com/open-telemetry/community/blob/main/project-management.md)
+for the details on how to start.
+
+Refer to the [How to define new conventions](/docs/general/how-to-define-semantic-conventions.md)
+document for guidance.
+
 ### Prerequisites
 
 The Specification uses several tools to check things like style,

docs/general/how-to-define-semantic-conventions.md

@@ -0,0 +1,154 @@
+<!--- Hugo front matter used to generate the website version of this page:
+linkTitle: How to define new semantic conventions
+--->
+
+# How to define new semantic conventions
+
+**Status**: [Development][DocumentStatus]
+
+<!-- toc -->
+
+- [Defining new conventions](#defining-new-conventions)
+  - [Best practices](#best-practices)
+    - [Defining attributes](#defining-attributes)
+    - [Defining spans](#defining-spans)
+    - [Defining metrics](#defining-metrics)
+    - [Defining resources](#defining-resources)
+    - [Defining events](#defining-events)
+- [Stabilizing existing conventions](#stabilizing-existing-conventions)
+  - [Migration plan](#migration-plan)
+
+<!-- tocstop -->
+
+This document describes requirements, recommendations, and best practices on how to define conventions
+for new areas or make substantial changes to the existing ones.
+
+## Defining new conventions
+
+- New conventions MUST have a group of codeowners. See [project management](https://github.com/open-telemetry/community/blob/main/project-management.md) for more details.
+  <!-- TODO: add CI check for CODEOWNERS file (when a new area is added) -->
+- New conventions SHOULD be defined in YAML files. See [YAML Model for Semantic Conventions](/model/README.md) for the details.
+- New conventions SHOULD be defined with `development` stability level.
+- New conventions SHOULD include telemetry signal definitions (spans, metrics, events, resources, profiles) and MAY include new attribute definitions.
+
+### Best practices
+
+> [!NOTE]
+>
+> This section contains non-normative guidance.
+
+#### Defining attributes
+
+Reuse existing attributes when possible. Look through [existing conventions](/docs/attributes-registry/) for similar areas,
+check out [common attributes](/docs/general/attributes.md).
+Semantic conventions authors are encouraged to use attributes from different namespaces.
+
+Consider adding a new attribute if all of the following apply:
+
+- It provides a clear benefit to end users by enhancing telemetry.
+- There is a clear plan to use the attributes when defining spans, metrics, events, resources, or other telemetry signals in semantic conventions.
+- There is a clear plan on how these attributes will be used by instrumentations
+
+Semantic convention maintainers may reject the addition of a new attribute if its benefits
+and use-cases are not yet clear.
+
+When defining a new attribute:
+
+- Follow the [naming guidance](/docs/general/naming.md)
+- Provide descriptive `brief` and `note` sections to clearly explain what the attribute represents.
+  - If the attribute represents a common concept documented externally, include relevant links.
+    For example, always link to concepts defined in RFCs or other standards.
+  - If the attribute's value might contain PII or other sensitive information, explicitly call this out in
+    the `note`.
+
+    Include a warning similar to the following: <!-- TODO: update existing semconv -->
+
+    ```yaml
+      - id: user.full_name
+        ...
+        note: |
+          ...
+
+          > [!WARNING]
+          >
+          > This attribute contains sensitive (PII) information.
+    ```
+
+- Use the appropriate [attribute type](https://github.com/open-telemetry/weaver/blob/main/schemas/semconv-syntax.md#type)
+  - If the value has a reasonably short (open or closed) set of possible values, define it as an enum.
+  - If the value is a timestamp, record it as a string in ISO 8601 format.
+  - For arrays of primitives, use the array type. Avoid recording arrays as a single string.
+  - Use the template type to define attributes with dynamic names (only the last segment of the name should be dynamic).
+    This is useful for capturing user-defined key-value pairs, such as HTTP headers.
+  - Represent complex values as a set of flat attributes. <!-- This may change, check out https://github.com/open-telemetry/semantic-conventions/issues/1669 to monitor the progress -->
+- Define new attributes with `development` stability.
+- Provide realistic examples
+- Avoid defining attributes with potentially unbounded values, such as strings longer than
+  1 KB or arrays with more than 1,000 elements. Such values should be recorded in the log or event body instead. <!-- This may change, check out https://github.com/open-telemetry/semantic-conventions/issues/1651 to monitor the progress -->
+
+Consider the scope of the attribute and how it may evolve in the future:
+
+- When defining an attribute for a narrow use case, think about potential broader use cases.
+  For example, if creating a system-specific attribute, evaluate whether other systems
+  in the same domain might need a similar attribute in the future.
+
+  Similarly, instead of defining a simple boolean flag indicating a success or failure, consider a
+  more extensible approach, such as using a `foo.status_code` attribute to include additional details.
+
+- When defining a broad attribute applicable across multiple domains or systems,
+  check for existing standards or widely accepted best practices in the industry.
+  Avoid creating generic attributes that are not based on established standards.
+
+> [!NOTE]
+>
+> When defining conventions for areas with multiple implementations or systems — such as databases,
+> or cloud providers — it can take time to strike the right balance between being
+> overly generic and not generic enough.
+>
+> Start with experimental conventions, document how they apply to a diverse range
+> of providers, systems, or libraries, and prototype instrumentations.
+>
+> The end-user experience should serve as the primary guiding principle:
+>
+> - If the attribute is expected to be used in general-purpose metrics for the area,
+>   consider introducing a common attribute.
+>
+>   For example, most messaging systems have a concept like a queue or topic.
+>   Queue or topic names are critical for latency and throughput metrics and
+>   equally important for spans to debug and visualize message flow.
+>   This indicates the need for a generic attribute representing any type of messaging destination.
+>
+> - If the attribute represents something useful in a narrow set of scenarios or
+>   is specific to certain system metrics, spans, or events, it likely does not need to be generic.
+
+#### Defining spans
+
+TBD
+
+#### Defining metrics
+
+TBD
+
+#### Defining resources
+
+TBD
+
+#### Defining events
+
+TBD
+
+## Stabilizing existing conventions
+
+- All conventions MUST be defined in YAML before they can be declared stable
+- Conventions that are not used by instrumentations MUST NOT be declared stable
+
+TODO:
+
+- prototyping/implementation requirements
+- migration plan
+
+### Migration plan
+
+TODO
+
+[DocumentStatus]: https://opentelemetry.io/docs/specs/otel/document-status