Split domain ownership without splitting every shared table first

• Decompose the overloaded entity into facts and decisions: legal identity, billing account, credentials, support relationship, and sales profile may have different owners. Identify shared invariants and consumers.

• Map change frequency, cross-team edits, direct writes, query patterns, and incident ownership. The primary bottleneck may be decision ambiguity rather than database throughput.

• Each fact and command has one accountable owner, consumers receive stable read contracts, unauthorized writes stop, and physical migration can happen later without changing semantics again.

• Create domain services or modules that own commands and publish canonical facts, while a composed customer view serves cross-domain reads. Enforce database roles, API contracts, and an ownership catalog even if storage remains shared initially.

• Commands route to the owning domain; domain events update composed projections. Shared identifiers link facts without giving every team permission to mutate the aggregate.

• Keep shared-table transactions where necessary during transition, but make cross-domain invariants explicit and assign a coordinator. Derived views are eventually consistent with freshness contracts.

• If a domain owner is unavailable, reject or queue its mutation rather than allowing another team to write tables directly. Projections reconcile from source facts and expose stale status.

• Database and service permissions follow fact ownership, tenant context, and purpose. Support tools issue domain commands rather than privileged direct updates.

• Track cross-owner code changes, direct writes, contract usage, projection lag, denied mutations, and decision lead time. Ownership is effective only if incidents and roadmap questions route correctly.

• Logical ownership yields organizational value before paying for data duplication. Split physical stores when scale, failure, compliance, or delivery benefit exceeds synchronization cost.

• One canonical mega-entity feels simple but centralizes every decision; full duplication gives autonomy but creates conflicting truth. Own individual facts and compose views.

• Publish the fact map, assign owners, wrap writes, revoke direct access, build projections, then move storage domain by domain only where justified.

• Staff candidates separate semantic ownership from physical placement. They reduce coordination by assigning decisions, not by blindly copying shared data into every service.

Interviewer evaluation rubric