Identity and Persistence

In this part we’ll have a closer look at the identity of the things we keep data of. One could argue that this is mostly a ‘pattern of miscommunication’ however, this one requires a little more background to understand so we treat it separately.

The question about identity is about wondering about what one is thing and it being the same. This becomes relevant when dealing with aboutness and master data management: when we are wondering whether we have two records about the same thing in multiple information systems. So in the context of data management, having an understanding of the nature of identity is prerequisite.

What is Identity?

Identity is about sameness. There are two important narrower concepts of Identity:

• Qualitative Identity is when thing share properties. For example: the two cars parked in front of my house both have wheels (four of them).
  • This concept helps us classify things and this will be discussed in more detail in the part on models of meaning
• Numerical Identity requires absolute and total qualitative identity. Numerical identity is the relation that a thing has to itself.
  • This is the subject we’ll look at here.

From here on out, we’ll use the term ‘identity’ to refer to the concept of numerical identity.

Numerical identity over time

The above definition of (numerical) identity seems simple enough. However, we will soon find that it only ever has real world application and meaning at single points in time. This is problematic because our information requirement typically spans over time.

Ship of Theseus

One thought experiment that describes our problem is a story about the Ship of Theseus. Imagine the ship that is owned by Theseus. It is built and then gets used over time. As the ship gets older, more and more of its parts are replaced, until the ship no longer contains any of the parts that it was originally constructed with.

If we use the definition of (numerical) identity as given above, we must conclude that the later ship does not have the same identity as the original ship. Yet, we think of it as the same ship. There is an extension of the thought experiment where someone collected all the parts as they got replaced, and then decides to build the original ship with its original parts. From a physical perspective this would be the future identity of the ship of Theseus, but Theseus himself at the same time still has a ship that he calls his own, so he wouldn’t think of the rebuilt ship as the same ship.

Note

Sometimes, you find that while you are writing up what you know, you realize that some other people have tried to convey the same knowledge in a different, perhaps much better way.

“Courtesy of kurzgesagt.org”

This Kurzgesagt video applies these concepts to us as individuals, but we can easily imagine this applying to anything we store data about.

Numerical identity is not what we are interested in

The understandable question is to wonder when the original ship stopped being the same ship and became another ship. However, that question is pointless: the moment the original ship got a single scratch, the ‘absolute and total qualitative identity’ condition is no longer met and we are then dealing with two identities, and therefore ‘no longer the same thing’.

Apparently, the matter in our body is mostly replaced every seven to ten years. Yet, we as people think of ourselves as ‘I’ and while we know that we change as people, there is still a sense of self that persists. This makes intuitive sense and it is also what our legal systems rely one: I can go to prison today for a crime that I committed last week. It would be surprising to have a judge accept the argument that I cannot be punished for that crime because I do not have the same identity as the person who committed the crime. So clearly, numerical identity is not what we are after.

Identity for all intends and purposes

This seems to pose a problem to our definition of identity. And yet, philosophers would say “there are no philosophical problems about identity”. The consensus seems to be that the nature of what 1 thing is, depends on what we are interested in. Looking at the Ship of Theseus, there are two perspectives. If we are concerned with ordering new parts for the ship, we care about its physical nature. From that perspective a broken rudder getting replaced by a new one, constitutes a new rudder identity and is something completely different form repairing the rudder: different processes, different parties involved. If we care about using the ship we look at things differently. A ship needs a rudder to steer. It had a rudder to steer, now it still has a rudder to steer. The functioning of the rudder was briefly interrupted while it was broken and then it got fixed. We don’t care how the failure of the rudder was resolved, we just care that it got resolved.

Conclusion

So how we resolve the question about the Ship of Theseus is more about how we want to resolve it, that it is about the nature of identity. But that doesn’t mean it has no effect on identity. In fact: The maintainer of the ship and the user of the ship have a different perspective on how the ship remains identical over time, this means that they look at two different identities. This means that in our data management processes,we need to manage these two identification keys (ID’s): one that represents the physical ship, one the functional ship. The relationships between these ID’s changes over time. Understanding this, as an organization, matters because the people who use ships and the people that repair ships need to be able to cooperate and communicate with each other: No ship no usage, no usage no need for a ship.