Architecture Heuristic YNIA: Events metadata

A while ago, I have continued with YNIA, which is a set of patterns I set up before really need them.

I work a lot (and enjoy working with) Event Sourced systems.

Events are composed of two parts:

• The business part (which is usually found during Event Storming sessions)
• Metadata (also called envelope), mostly a technical concern

Usually metadata are quite thin:

• UUID
• Creation date
• (Stream ID)
• (Position (index) in the stream)

The great thing about event sourcing is that it captures exactly what happened, which is an issue if you didn't captured enough, the problem is two-folds:

• You have forgotten an element in the business part: you can try to rebuild an enriched stream
• You have forgotten an element in the metadata part: good luck!

Metadata are a technical concern, until they became a business concern.

That's why I add the following elements:

• Occurring time: when the event happened in real-life (see bi-temporality)
• Actor: who (the person) did the action, it is the person in charge of the delegation (leading to "on behalf of")
• Initiator/on behalf of: who requested the action to be performed leading to the event
• Distributed trace identifiers: to be able to fetch the traces associated
• Origin system: usually en API or a batch/asynchronous process
• Origin system version: usually a deployment version/hash

It is not much, but it covers all the business cases I have faced until now.