[new rule] add a rule(set) to clearly specify how data change events should be used

(i) This issue has been manually transferred from a former internal repository, as a private repository issue cannot be transferred to a public repository.

Context

Data change events usually do not contain semantical information of why a change happened. This is why the usage of data change events should be limited. Deducting business decisions from data change events implicitly requires domain knowledge of a foreign domain, thus reducing encapsulation.

A rule (or a set of rules) should be created to clearly state how data change events should be used.

Possible rules:

• SHOULD use data change events for data replication
• SHOULD be used for updating otherwise read-only data sources. The only purpose of these read-only data sources is for consumption (e.g. by UIs, report generation, statistics).
• MUST NOT be used to implement policies (automation rules) that issue business side effects (commands) to any API.
• MUST NOT deduct intention from data change events

No file, test, or entry point is identified in the issue. Start by reviewing the repository’s existing asynchronous and event guidelines, then confirm the intended scope and wording with maintainers. Done means an agreed rule or rule set is added to the appropriate guideline document with clear usage boundaries.