OpenTelemetry concept: a single underlying datum with high cardinality (many unique keys) and high dimensionality (each key can take many values). Traces, spans and events are facets of the same wide event. Spans carry a timestamp, extra attributes, and a human-readable message; events can belong to a span. Because upcoming data shapes aren't known in advance, schemaless databases are considered a good fit for wide-event storage even though they are poor transactional stores.