Move non-otlp.md to common directory (#2587)

specification/common/mapping-to-non-otlp.md

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+# OpenTelemetry Transformation to non-OTLP Formats
+
+**Status**: [Stable](../document-status.md)
+
+All OpenTelemetry concepts and data recorded using OpenTelemetry API can be
+directly and precisely represented using corresponding messages and fields of
+OTLP format. However, for other formats this is not always the case. Sometimes a
+format will not have a native way to represent a particular OpenTelemetry
+concept or a field of a concept.
+
+This document defines the transformation between OpenTelemetry and formats other
+than OTLP, for OpenTelemetry fields and concepts that have no direct semantic
+equivalent in those other formats.
+
+Note: when a format has a direct semantic equivalent for a particular field or
+concept then the recommendation in this document MUST be ignored.
+
+See also additional specific transformation rules for
+[Jaeger](../trace/sdk_exporters/jaeger.md) and [Zipkin](../trace/sdk_exporters/zipkin.md).
+The specific rules for Jaeger and Zipkin take precedence over the generic rules defined
+in this document.
+
+## Mappings
+
+### InstrumentationScope
+
+OpenTelemetry `InstrumentationScope`'s fields MUST be reported as key-value
+pairs associated with the Span, Metric Data Point or LogRecord using the following mapping:
+
+| OpenTelemetry InstrumentationScope Field | non-OTLP Key | Notes |
+| ------------------- | --- | --- |
+| `InstrumentationScope.name`|`otel.scope.name`|since 1.10.0|
+| `InstrumentationScope.version`|`otel.scope.version`|since 1.10.0|
+
+The following deprecated aliases MUST also be reported with exact same values for
+backward compatibility reasons:
+
+| non-OTLP Key | Alias for | Notes |
+| --- | --- | --- |
+|`otel.library.name`|`otel.scope.name`|deprecated since 1.10.0|
+|`otel.library.version`|`otel.scope.version`|deprecated since 1.10.0|
+
+### Span Status
+
+Span `Status` MUST be reported as key-value pairs associated with the Span,
+unless the `Status` is `UNSET`. In the latter case it MUST NOT be reported.
+
+The following table defines the OpenTelemetry `Status`'s mapping to Span's
+key-value pairs:
+
+|OpenTelemetry Status Field|non-OTLP Key|non-OTLP Value|
+|--|--|--|
+|Code | `otel.status_code` | Name of the code, either `OK` or `ERROR`. MUST NOT be set if the code is `UNSET`. |
+|Description | `otel.status_description` | Description of the `Status` if it has a value otherwise not set. |
+
+### Dropped Attributes Count
+
+OpenTelemetry dropped attributes count MUST be reported as a key-value
+pair associated with the corresponding data entity (e.g. Span, Span Link, Span Event,
+Metric data point, LogRecord, etc). The key name MUST be `otel.dropped_attributes_count`.
+
+This key-value pair should only be recorded when it contains a non-zero value.
+
+### Dropped Events Count
+
+OpenTelemetry Span's dropped events count MUST be reported as a key-value pair
+associated with the Span. The key name MUST be `otel.dropped_events_count`.
+
+This key-value pair should only be recorded when it contains a non-zero value.
+
+### Dropped Links Count
+
+OpenTelemetry Span's dropped links count MUST be reported as a key-value pair
+associated with the Span. The key name MUST be `otel.dropped_links_count`.
+
+This key-value pair should only be recorded when it contains a non-zero value.