In discussing my definition of a digital identity, Stefan Brands has asked, “What is a digital subject – and why not an entity in general?” A great question.
Let me quote from the Oxford English Dictionary. A “subject” is “a person or thing that is being discussed, described or dealt with.” “Digital” means “relating to or using signals or information represented by discrete values of a physical quantity.” So I interpret “digital subject” as a “person or thing represented or existing in the digital realm which is being described or dealt with”. “Dealt with’ is a great concept, and pertains to much of what we do in computing.
I think it is essential – not optional – to make it clear that the digital world includes many things which need to be “dealt with” other than humans. First and formost are the devices which allow us to penetrate the digital realm, and the digital resources which attract us to it. Beyond that are policies and relationships with other digital subjects (e.g. between humans and devices or documents or services). These policies and relationships are then themselves things that must be dealt with.
The OED goes on to define subject, in a philosophical sense, as the “central substance or core of a thing as opposed to its attributes”. I take “attributes” precisely as characteristics which are expressed in claims, so from this point of view, also, “subject” is the perfect word.
As for “entity”, the OED defines it as “a thing with distinct and independent existence”. The independent existence of the thing is a moot point here – it may well be an aspect of something else. Instead, what is most important about the entity is that it is being dealt with by some relying party and thus claims are made about it. So “subject” is a better word than ‘entity”.