When I hear the words 'single source of truth' I often pause and think for a moment to understand the context of the sentence. Here are my thoughts on what it means to me using the healthcare domain.
Often what we mean is a single place to go and find out everything we need to know about a patient. The main focus being on the word 'single'. I want the many truths and I want to go to a single place and find it. Sometimes we have to combine single sources of truths though to build up a more complete picture.
Some examples of this are GP records, the GP has a longitudinal view of a patient healthcare record. It has a view of the truth and is a single place we can go for it. It doesn't necessarily hold all the data we need though, just a view of it so not always the full truth.
This is different to the source of a single truth where the focus is on the word 'truth'. The truth is where the data originates, usually tied to an event of some sort. It may be replicated to other places, but the truth still rests at the source.
Examples of this would be an episode of care in a hospital in a particular specialty or a laboratory. This is where the truth is recorded, it can be replicated, summarised, shared or accessed via API's or sent back to a GP, so they have the most complete holistic picture but they don't always get the whole truth.
There are a lot of sources of truth when it comes to healthcare data, I find it really helpful to know if I am dealing with a single source, or a single truth when using data for specific use cases.
I don't believe a single source of the truth (and nothing but the truth) exists in healthcare, even if many people believe this can happen, I am not sure it will or if it should.