Paperwork and public services
ADA (Diavgeia online posting number)
In short
The unique code every public decision gets when it is posted on Diavgeia.
The ADA is the "ID" of a decision on Diavgeia. It is created when the decision has been fully registered, and it is printed automatically on every page of the posted document.
A decision has only one ADA. If the decision is cancelled, its ADA stays inactive and is not given to another one.
Example: you receive a decision from your municipality. Copy the ADA from the page and search for it on Diavgeia to see that the decision was posted and which text is the official one.
Official source: Diavgeia