Suppose you have a paperback copy of The Hobbit. I have an identical-looking copy. Are we holding the same book? There are a couple of ways to answer this:
- No. I could shred my book and your book would be unaffected.
- Yes. We could swap copies and both of us would still have the same book.
Now suppose you have the same paperback copy of The Hobbit, but I have an older hardcover copy (with more tasteful cover art). Besides the fact that we're swapping items, is (2) still valid? Do we still end up with the same book-not-as-item that we started with?
You're probably thinking "yes." We don't tend to think of different editions as different "books." Still, it's worth making the distinction. You can't order just The Hobbit from Amazon.com; you must choose a paperback edition, a mass market paperback edition, a hardcover edition, an audio CD edition, or a Kindle edition. These are different ways of wrapping up and presenting — of manifesting — the same essential content, i.e. the text of The Hobbit.
Let's take this one final step. This time you and your book club friends have spent the last month reading The Hobbit in a variety of editions: paperback, e-book, audio CD, etc. No problem! You all read or heard the same text, so you can have a great discussion about the text. Then I show up and say I watched a film version, or played a video game, or attended the ballet. What did I do that's so different from the variety of ways the rest of you experienced The Hobbit? I watched (or played) a different expression of The Hobbit. It's not just that the wrapping was different; someone created new content.
Still, Tolkien's text and the upcoming film adaptation of The Hobbit are highly related. They will share characters, theme, plot, and many of the same lines. They can be considered different expressions of the same work, broadly speaking.
What's the point of the WEMI model? Searching and browsing tools which make these kind of distinctions can help users find what they need more efficiently. Interests may vary anywhere from a cultural studies student writing a paper on the different expressions of The Hobbit...to a collector interested in a specific, physical volume.
For some people, these four levels are not fine-grained enough, or just don't fit with the shape of their interests. For example, does a Japanese translation of The Hobbit count as a different manifestation, or a whole new expression? How much can two expressions differ and still be covered by one broad work? These concerns don't mean WEMI is wrong; it just means WEMI isn't right for every purpose. But what conceptual model is? Even models of unquestionably objective features of the world, like subway maps, can legitimately bow to both facts and interests...so long as we understand what's going on and why.