System integration

Where two systems disagree

The hard part of an integration is almost never the connection. It is that the two systems mean different things by the same word: a customer in one is a company and in the other a person, a date is a delivery in one and an invoice in the other, a status exists in one and has no equivalent at all.

The mapping document is where those disagreements are decided and written down, once, rather than encoded in somebody's head and rediscovered during an audit.

• Field-by-field mapping, with a written decision wherever there is no match
• Retries and idempotency, because networks fail and duplicates are worse than delays
• A test suite covering the edge cases, which is where integrations actually break
• Monitoring with alerts to a person, not to a log nobody reads
• Technical documentation, so this is maintainable by somebody else

When a system has no API

There is almost always a route: a scheduled export, a database connection, a scripted interface. We establish which one before quoting rather than discovering it halfway through, because the answer changes the cost by a multiple.

The code and the credentials are yours regardless of where it runs. An integration you cannot move is a dependency rather than an asset.