# OpenTracing ## OpenTracing Attributes Attributes used by the OpenTracing Shim layer. | Attribute | Type | Description | Examples | Stability | |---|---|---|---|---| | `opentracing.ref_type` | string | Parent-child Reference type [1] | `child_of`; `follows_from` |  | **[1] `opentracing.ref_type`:** The causal relationship between a child Span and a parent Span. --- `opentracing.ref_type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used. | Value | Description | Stability | |---|---|---| | `child_of` | The parent Span depends on the child Span in some capacity |  | | `follows_from` | The parent Span doesn't depend in any way on the result of the child Span |  |