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D2.13: Virtual Persons and Identities

Physical entities and virtual entities  D2.13 Virtual Persons


Links between entities

Links between physical entities and virtual entities

According to the above-mentioned dualistic separation between a physical and a virtual world, the model proposed in this document has two distinct, but interconnected layers at any specific time T. The interconnection consists of individual links between physical and virtual entities existing at time T. We say that such a (direct) link between two entities exists, if the physical entity is represented by the virtual entity, or vice versa, if the physical entity represents the virtual entity at this point in time.

In this way, a particular physical entity may be linked to many virtual entities, and a particular virtual entity may be linked to many physical entities (while some entities may not be linked at all). Note that links are supposed to exist at time T, i.e., new links may arise and outdated links may disappear over the course of time. This is the dynamic component of our model. In mathematical terms, we assume thus a time-dependent n-to-n relation between the sets of currently existing physical and virtual entities. This relation tells us precisely which entities are linked and which are not linked to each other at a particular point in time. It can be represented by a bipartite graph connecting the two worlds.

Examples of links between physical and virtual entities are shown in the following list.

  1. The “Empire State Building” (a physical entity) is linked to the virtual entity “The world’s tallest building in 1950

  2. The physical person “Neil Armstrong” is linked to the virtual person “The first man to walk on the moon

  3. A specific human player (a physical person) of an online role-playing game is linked to the avatar (a virtual person) under her control

  4. The football players “T. Henry” and “Ronaldinho” (two distinct physical persons) are both linked to the virtual person “Player of F.C. Barcelona

  5. The physical person “Steve Jobs” is currently linked to the virtual person “CEO of Apple Inc.



At any point in time, we call a “subject” of a virtual person, any physical entity that is linked to this virtual person at that time. The subject can be a physical person, a cyborg, an animal, the wind, a specific instance of a computer-program, etc.

The collection of subjects for a given virtual person is time-dependant. It can even be empty either for a certain period of time, or forever. For example, the virtual person “The first man to walk on the sun” will very likely never have any subject linked to it. 

Let’s consider the virtual person “The first man to walk on the moon”. Before the 20th of July 1969, there was no subject linked to this virtual person. Since the Eagle has landed and Neil Armstrong has put his feet on the surface of the moon, the physical person Neil Armstrong will be the only living subject ever linked to this virtual person. After Armstrong’s death, when his body will have disappeared, there will be no physical entity linked to this virtual person anymore.

The concept of subject, in the physical world, allows also to handle in a similar way physical entities of different nature that share, for example, some acting capabilities or some identity-related characteristics. 


Links between physical entities or between virtual entities

To further augment the generality and possibilities of the proposed model, we may also consider a similar type of (direct) link between two physical entities or between two virtual entities. For example, by its legal empowerment to act on behalf of the company under her guidance, we may link the virtual entity “CEO of Apple Inc” to the virtual entity “Apple Inc.”. A picture of the Eiffel Tower is a physical entity that represents the Eiffel Tower. Therefore, there is a link according to our model between the Eiffel Tower (a physical entity) and its picture (another physical entity).

Such links between two entities of the same type can then be used to establish indirect links over corresponding chains of direct links. For example, we may link the physical entity “Steve Jobs” indirectly, that is via the virtual entity “CEO of Apple Inc.”, with the virtual entity “Apple Inc.”. This mechanism gives our model a recursive component.


An identity of a physical entity is described in Section . In particular, it depends on the ability of the observer to see the link between the entity and its corresponding identifying information.

In the virtual world, as we will see in Section , the link between a virtual entity and some identifying information is always visible.


Being the product of someone’s mind or imagination does not give a virtual entity its identity. However, any identity-related information defines a unique virtual entity: the abstract entity for which this information is tautologically an identity. In other words, any identifying information becomes the “tautological identity” of its corresponding virtual entity.

The tautological identity of a virtual entity is valid for any observer and becomes therefore independent from the observer(s). 

As a consequence, there is no reason to make a distinction between “identifying information” and “identity”, in the virtual world. Let’s consider again the example of a fingerprint. “The one who is characterized by this fingerprint” is a virtual person whose tautological identity is the information contained in this fingerprint. Any observer can link this information and this virtual person. In the virtual world, the tautological identity is in line with traditional definitions of the term “identity” that make it independent from the observer. 

The tautological identity is time-invariant; it is a property of the corresponding virtual entity.  

A defined virtual entity has a unique tautological identity in the virtual world. Therefore, there is a one-to-one correspondence between defined virtual entities and their tautological identities:

one virtual entity


its tautological identity

Only defined virtual entities can be virtual persons. Therefore, in the virtual world, we also have the following one-to-one correspondence:

one virtual person   


its tautological identity

Virtual identity

As we have seen, any identity-related information defines a unique corresponding virtual entity: the abstract entity for which this information is the tautological identity. All entities characterized by this (partially) identifying information are linked to this virtual entity.  

A “virtual identity”, for a given entity, is the identity of a virtual entity linked to this given entity. Both physical and virtual entities can have virtual identities.

A virtual identity, for a subject, is the identity of a virtual person linked to this subject.

Pseudonyms form an important family of virtual identities. Indeed, the pseudonym “Gauss375” is the tautological identity of its corresponding virtual person (“the one called “Gauss375”), which in turn is linked to the physical person(s) using the pseudonym. The virtual person creates an indirection between the pseudonym and its user(s).


Figure : A pseudonym is a virtual identity for its user(s)


Virtual identities emphasize the indirection between acting subjects and the identifying information related to their actions and/or the objects supporting these actions. the ISO/IEC 4th Working Draft 24760: “reference to a unique object that is used by an entity to be uniquely represented within a specific domain or process; the purpose of an identifier is to provide entities with means of representation independent of the entity’s identity in a given context without necessarily revealing the entity’s identity; the validity of the identifier is limited to the object life cycle.”

Actually, “identifiers” as they are defined in the ISO/IEC 4th Working Draft 24760 are covered by the concept of “virtual identities” which are also identifiers (identifying information) according to our definition. However, in our model, (partial) identifiers are more general and are not limited to virtual identities. 

Virtual entities can have virtual identities too.  

This happens whenever a virtual entity is linked to another virtual entity: the tautological identity of one virtual person becomes the virtual identity of the other one. 




Figure 10: Virtual identity of a virtual entity



Physical entities and virtual entities  fidis-wp2-del2.13_Virtual_Persons_v1.0.sxw  Conclusion
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