Thursday, July 06, 2006

Ambiguity and Identity 

Uniqueness does not prevent ambiguity. Consider a fingerprint. Fingerprints have for some time been used to identify suspects in criminal investigations. A human fingerprint is considered unique, except in the case of identical twins. It would seem to be an ideal identifier for a person. But it might also be used for many other purposes. A gruesome example, after an airliner crash, a fingerprint could be used to identify a finger, or a hand, or an arm. On the other end of the scale, that same fingerprint could be used to identify my nuclear family, since no other family can possibly have a member with the same fingerprint. For the same reason, it could be used to identify a football team, a nation, or a species. It is a unique, distinguishing characteristic all right - of many, many things. By itself, it is not clear which of these a fingerprint identifies.

Numerals are also identifiers - of numbers. For example, the numeral "6" identifies the number 6. It lets you pick out the number 6 from any other number. It does not identify 6.00001 or 5.9999999. It identifies 6. So it is a good identifier. It is unique and unambiguous. Or is it. Six of what? It is my sons age in the phrase "Joshua is 6 years old." It is one half of a year, when counting months, as in "6 months".

But the web is an information space. And URIs identify information resources. Suppose you have an set of information resources each mapped to a unique URI, just as I did with my blue drinking glasses in Anatomy of a Reference. Now how does that help distinguish one resource from another? Suppose the resources are all copies of the same .jpg image stored in different locations. Just having a unique URI that can access each different copy of the image doesn't help us distinguish one of the images from another - they are all alike. Unless, of course, we attach the URI to the image. But that would alter the information contained in the image, making them different resources. It may be objected, "But it doesn't matter, they are all the same." Not if they are one of compliance buttons, such as "". The copy on my site means that my site is compliant, the copy on your site means that your site is compliant. See Level Triple-A Conformance to Web Content Accessibility Guidelines 1.0. Thus the information they communicate is different, even though the representations are the same. If I were to collect a dozen of them and store them in directories on my machine, I could not for the life of me distinguish one from the next, even though they are each retrievable by a unique URI from somewhere else. Just being accessible by a unique URI does not help me identify the different claims made by each one when they are collected and stored on my machine. This is because being accessible by a URI does not, in itself, add any distinguishing characteristic to the resource.


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Prior Art


"We are in the habit, I take it, of positing a single idea or form in the case of the various multiplicities to which we give the same name. Do you not understand?" "I do." "In the present case, then, let us take any multiplicity you please; for example, there are many couches and tables." "Of course." "But these utensils imply, I suppose, only two ideas or forms, one of a couch and one of a table." "Yes." "And are we not also in the habit of saying that the craftsman who produces either of them fixes his eyes on the idea or form, and so makes in the one case the couches and in the other the tables that we use, and similarly of other things? For surely no craftsman makes the idea itself. How could he?" "By no means."
Plato, Republic X, page 596a

David Hume

"This convention is not of the nature of a promise: For even promises themselves, as we shall see afterwards, arise from human conventions. It is only a general sense of common interest; which sense all the members of the society express to one another, and which induces them to regulate their conduct by certain rules. I observe, that it will be for my interest to leave another in the possession of his goods, provided he will act in the same manner with regard to me. He is sensible of a like interest in the regulation of his conduct. When this common sense of interest is mutually expressed, and is known to both, it produces a suitable resolution and behaviour. And this may properly enough be called a convention or agreement betwixt us, though without the interposition of a promise; since the actions of each of us have a reference to those of the other, and are performed upon the supposition, that something is to be performed on the other part. Two men, who pull the oars of a boat, do it by an agreement or convention, though they have never given promises to each other. Nor is the rule concerning the stability of possession the less derived from human conventions, that it arises gradually, and acquires force by a slow progression, and. by our repeated experience of the inconveniences of transgressing it. On the contrary, this experience assures us still more, that the sense of interest has become common to all our fellows, and gives us a confidence of the future regularity of their conduct: And it is only on the expectation of this, that our moderation and abstinence are founded. In like manner are languages gradually established by human conventions without any promise. ..." - A Treatise of Human Nature, Chapter 74 by David Hume

John Locke

"...Semeiotike, or the doctrine of signs; the most usual whereof being words, it is aptly enough termed also Logike, logic: the business whereof is to consider the nature of signs, the mind makes use of for the understanding of things, or conveying its knowledge to others. For, since the things the mind contemplates are none of them, besides itself, present to the understanding, it is necessary that something else, as a sign or representation of the thing it considers, should be present to it: and these are ideas. And because the scene of ideas that makes one man's thoughts cannot be laid open to the immediate view of another, nor laid up anywhere but in the memory, a no very sure repository: therefore to communicate our thoughts to one another, as well as record them for our own use, signs of our ideas are also necessary: those which men have found most convenient, and therefore generally make use of, are articulate sounds. The consideration, then, of ideas and words as the great instruments of knowledge, makes no despicable part of their contemplation who would take a view of human knowledge in the whole extent of it. And perhaps if they were distinctly weighed, and duly considered, they would afford us another sort of logic and critic, than what we have been hitherto acquainted with." - AN ESSAY CONCERNING HUMAN UNDERSTANDING by John Locke 1690