The Work

A thought on identifiers and books

In mid-March of 2006, NISO convened a roundtable of experts and thought leaders in digital resources, at the National Library of Medicine in Bethesda, Maryland. The goal of this meeting was to establish some consensus around the use of identifiers for text, video, music, and other media in the digital realm. In breakout discussions, three characteristics of an identifier were ultimately defined: granularity, semantic opacity, and persistence.

The granularity of an identifier refers to precisely what it identifies. An ISBN, for example, identifies a stand-alone, trade-able publication (a book or a chapter). It does not identify an illustration, a diagram, a bibliography. The publication is the extent of the ISBN’s granularity. Other identifiers (such as the DOI) can identify components of publications.

Semantic opacity refers to the degree to which the identifier is a “dumb number” – a random string of numbers that carries no intelligence. The ISBN is only partly a dumb number – it begins with 978 or 979, which indicate that the thing being identified is in the book supply chain; it then has a publisher prefix. The string following the publisher prefix is semantically opaque, and the ISBN ends in a check-digit that validates the number.

Persistence refers to how long the relationship between the identifier and the object will last. Identifiers on shipping containers, for example, do not need to be persistent after the container has been unloaded and its contents dispersed. Identifiers on books need to be persistent for a much longer period of time, as information about a book can be created long after the book itself has gone out of distribution.

Essentially, all an identifier does is say, “This thing is not that thing.” It doesn’t say what the thing is, or offer any insight about any of the thing’s characteristics. An identifier expresses uniqueness. And that’s all it expresses.

7 thoughts on “A thought on identifiers and books

  1. Uniqueness within some domain. It does give some idea of what the thing is (e.g. your explanation of what an ISBN identifies).


  2. I think I understand what you mean when you say that an identifier “doesn’t say what the thing is or offer any insight about any of the thing’s characteristics”. But how does that fit with the idea that starting an ISBN with 978 tells us that the thing is book? I guess the number on its own doesn’t say that; another reference table tells us the nature of the thing.. yes?

    1. The problem with the ISBN is that it is not truly a dumb number. The 978 or 979 prefix tells us that it’s a book-ish thing. Then there’s the publisher prefix. Some publishers get horribly attached to their prefixes – but when there’s an acquisition or merger, the prefix ceases to mean what it used to. So it’s best to regard the ISBN as a dumb number in practice, even though it actually does have some intelligence in it.

      The same is true of phone numbers. Area codes shift, people move with their numbers, etc.

      Perhaps I should amend it to say the BEST identifiers don’t say what the thing is or offer any insight about its characteristics. Because the minute they do, problems of interpretation arise.

  3. Fantastic website you have here but I was curious if you knew of any message boards
    that cover the same topics discussed in this article?
    I’d really like to be a part of community where I can get responses from other experienced individuals that share the same interest. If you have any suggestions, please let me know. Kudos!

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