Robert Shimmin wrote:
I know of one fairly prominent commercial digital library (Eighteenth Century Online) that made the decision that the issues with using page numbers as unique identifiers are sufficiently hairy that they went with sequential *image* numbers (which are unique), and the database maintains as metadata the page number that goes with each image number (which may not be unique, sequential, numerical, or even present).
They may have a completely different usage case than we have. PG is an archive and its primary scope is preserving material. We also make this material accessible to outside people. One of the principal points in online archiving is the permanence of the url. If you keep moving things around people will not be able to reference your material. Putting all pages of a book into a container and numbering them in one sequence may work well if you don't have external references to the sequence number. It may also work well if you are sure, *really* sure that you won't ever go back and add or remove some pages from the collection. But if you want people to link to the page images *and* be able to insert or delete pages from the collection after the first publication you cannot use the single sequence numbering technique. Suppose we have published page images for "Alice in Wonderland". Suppose the first edition just contains the pages and does not contain separate images for the illustrations. Later somebody goes back and scans the illustrations in a better resolution and naturally wants them to be inserted in the right position. Using sequential numbering you are dead in the water. Suppose you have collected a lot of page images but thrown away the images of the cover pages if there was no text on them. Later you decide to add those images too. Again, using single-sequence numbering you are dead in the water. But if you used the true page numbers none of these changes poses the slightest problem because you never have to change the urls of the pages you published before. -- Marcello Perathoner webmaster@gutenberg.org