Integration fails without an authoritative source

Disconnected systems are often described as ‘we have no API’. The break is earlier: the same customer, order, or stock record is written in more than one place, and no one has said which copy is authoritative.

That is the definition in the system boundaries diagnosis. Every new system connected before the boundary is drawn multiplies the conflicting record.

What an authoritative source is

An authoritative source is the single writable copy of a record for a given fact. Other systems read that copy or request an update through a defined flow. If two systems write the same field independently, there is no authoritative source — there is synchronization. Synchronization moves the contradiction with a delay.

• Which entity is born in which system?
• Which fields may not be changed by another system?
• If an update request is rejected, what does the operation do?

Why integration comes after

System integration establishes the direction of a data flow, its contract, and its retry behaviour. Direction cannot be drawn if the authoritative source is unknown. A contract cannot be signed if it does not say which field belongs to whom.

That is why the integration note stands separately: system integration is done by contract. The first clause of the contract is the authoritative source.

What gets built

An entity list is drawn first. Write rights are assigned per entity. Reads and event notifications are kept separate. Conflicting records are stopped; they are not silently overwritten. The operation must be able to see a rejected update — otherwise visibility is lost.

This work often needs a dedicated record layer. A packaged product treats every entity as its own. At that point custom software becomes the system that holds the authoritative source; the others connect to it.

To make the source explicit, it is enough to say which records each current system writes. Discuss the scope.