At the LID developers' Wiki, I'm using the page, FOAF Fields, as a workspace as i'm reading through the FOAF Vocabulary Specification. A few minutes ago, the difference in where-it-is-coming-from between vCard and FOAF came to the fore. I take this occassion to offer some thoughts on the concepts, person and persona.

Wiki enables your feedback and ideas to be entered right there, by changing or replacing my text. Or by entering text at the discussion tab.

Or, if you are more blog than wiki, kindly blog and link back to here.

In vCard, that a vCard is the vCard of a person is implicit. Just as it is implicit, if we see a small paper card, about two inches by three and a half, with a name on it, that this is the calling card or business card of some person, and that other data on that card gives us information about that person and their relationships. Just as a person may have different business cards for different roles, so two different vCards can be vCards of the same person. But the vCard specification gives us no way to relate those two vCards.

One datum on a vCard is related to another by being within the same vCard. (Yes, or by being somehow linked to from a vCard, but forget that for this discussion.)

One datum in FOAF is related to another by property connections to an object.

A concrete example:

With vCard, organization is a text field, giving the name of the organization. We know 'NetMesh' is the name of the organization of Joaquin Miller, because we find it in the org field of a vCard and 'Joaquin Miller' in the formatted name field of that vCard.

With FOAF, instead, we know NetMesh is the organization of Joaquin Miller, because we find an organization link to an organization object with 'NetMesh' in the name property from the person object with 'Joaquin Miller' in the name property.

With vCard, we can't tell that Johannes is associated with the same organization as Joaquin. Perhaps there are two organizations with the same name, one headquartered in sunny Sunnyvale, and the other with address in foggy on a summer morning East Oakland. FOAF lets us know that this is the same NetMesh.

So you conclude FOAF is better? Let's judge goodness while considering intent. And let's not rush to judgement.

Permit me to go down this rabbit hole just a bit deeper.

Suppose one person has two vCards. Consider two cases:

Case 1: One vCard identifies the person as Deputy Assistant Undersecretary for Personas of the Department of Homeland Security, USofA. The other identifies that person as Member, Board of Directors, Society for Calming of the Polity. In this case, we have one person, with one {identity | persona | whatchewmightcallit}, in two roles, with a vCard for each role.

Case 2: One vCard identifies the person as Reporter, Daily Planet, Metropolis. The other identifies that person as Man of Steel. In this case, we have one person with two distinct and (except for we readers) unrelated {identities | personas | whatchewmightcallits}.

For vCard, these two cases are like water off that famous duck's back. If the first person profers two vCards, we all understand what is going on. (Someone might want to have a look at the law, to check on the limits on outside activities of officers of the government.) If Lois finds a copy of Superman's vCard on Clark's computer, that does not prove anything.

On the other hand, vCard has no way to link the two vCards in the first case and, therefore, no way to keep them separate in the second.

For FOAF, the identity data is linked to a person object. The first case is handled nicely by linking two sets of identity data to the same person object. (I don't know enough about FOAF yet to know if there is a mechanism for preventing the two sets of data from being jumbled. We can't have donors delivering money for the Society to the office of the Deputy Assistant Undersecretary. Well, we can and may do, but that's illegal, so it will be useful to avoid the jumble.)

The second case, on the other hand, is a problem for FOAF. If we believe in the semanticity of the web, then foaf:Person represents a person. FOAF groups the reporter's contact data as properties of the foaf:Person object representing Clark. How to group the man of steel's contact information, in case we need his help in dealing with the present situation? We can't group it using the object representing the reporter. But: if we group it using a different foaf:Person, we are lying and, more to the point, violating the FOAF specification.

Not to worry. Our LID model will deal with this. For now, though, we put aside these considerations and proceed with the project as planned.