Single source of truth
- Industry term
A single source of truth is the record everyone agrees decides a particular fact. Other copies can exist, and when they disagree, they follow that record.
Copies drift apart because each gets edited on its own, and nothing tells the others. With one record named as the decider, a disagreement becomes a lookup instead of a debate. Different facts can have different deciders, such as a billing system for whether someone paid and a profile page for their display name.
Where you’ll meet it
You ask your coding agent to change the email address on your personal website. The contact page now shows the new one, while the footer and the "Hire me" button still send mail to the old one, because the address was typed into each spot separately.
What to do
Tell the agent you want the address stored in one place in the code, with every page reading it from there. Ask it to search the project for other spots with the old address. Then preview the site and click each email link to see which address it opens.
Easy to mix up
A knowledge base holds a team's articles and how-to pages for browsing. A single source of truth can be as small as one fact in one spreadsheet cell, as long as everyone follows it.
Check yourself
A customer's mailing address is kept in your billing system, your support tool, and a shared spreadsheet. Customers who move almost always tell the support team first. Which should decide the address?
Go deeperCopies need rules for receiving changes and for showing their age
In data management, where the term is often shortened to SSOT, the deciding record may be a running log of events or a database spread across machines. Engineers then also settle whether each change is pushed out to the copies or the copies fetch changes on a schedule, and what the copies do while the original can't be reached.
When an assistant searches several places, each passage should arrive labeled with its source and the date it was saved. Without those labels, a “cache,” a copy kept for speed, can pass for the original after it goes stale.