The family therapist Salvador Minuchin declared, "The human experience of identity has two elements: a sense of belonging and a sense of being separate." This is as good a description of digital identity as it is of our psychological identity. A digital identity contains data that uniquely describes a person or thing but also contains information about the subject's relationships to other entities.

To see an example of this, consider the data record that represents your car, stored somewhere in your state or country's computers. This record, commonly called a title, contains a vehicle identification number (VIN) that uniquely identifies the car to which it belongs. In addition, it contains other attributes of the car such as year, make, model, and color. The title also contains relationships: most notably, the title relates the vehicle to a person who owns it. In many places, the title is also a historical document, because it identifies every owner of the car from the time it was made, as well as whether it's been in a flood or otherwise salvaged.

While fields as diverse as philosophy, commerce, and technology define identity, most are not helpful in building, managing, and using digital identity systems. Instead, we need to define identity functionally, in a way that provides hooks for us to use in making decisions and thinking about problems that arise in digital identity.

Joe Andrieu, principal at Legendary Requirements, writes that "identity is how we recognize, remember, and respond to specific people and things. Identity systems acquire, correlate, apply, reason over, and govern information assets of subjects, identifiers, attributes, raw data, and context." This definition is my favorite because it has proven useful over the years in thinking through thorny identity issues.

The identity record for a car includes attributes that the system uses to recognize it: in this case, the VIN. The title also includes attributes that are useful to people and organizations who care about (that is, need to respond to) the car, including the owner, the state, and potential buyers. The government runs a system for managing titles that is used to create, manage, transfer, and govern vehicles (or, in Andrieu's formulation, remember them). The system is designed to achieve its primary goal (to record valuable property that the state has an interest in taxing and regulating) and secondary goals (protecting potential buyers and creating a way to prove ownership).

Digital identity management consists of processes for creating, managing, using, and eventually destroying digital records, like the one that contains your car title. These records might identify a person, a car, a computer, a piece of land, or almost anything else. Sometimes they are created simply for inventory purposes, but the more interesting ones are created with other purposes in mind: allowing or denying access to a building, the creation of a file, the transfer of funds, and so on. These relationships and the authorized actions associated with them make digital identities useful, valuable, and sometimes difficult to manage.

Photo Credit: Plate - WHOS_CAR from Lone Primate (CC BY-NC-SA 2.0)