Q. What exactly is EEBO-TCP made of?
A. (digital) copies of (microfilm) copies of works.
A. Well, no. Specific copies of works, held in libraries. What I think FRBR calls “instances”.
Q. FRBR makes me think of unhappy cats. Can you give an example?
A. Consider Jeremy Taylor’s 1668 page-turner “XXV sermons preached at Golden-Grove being for the winter half-year beginning on Advent-Sunday until Whit-Sunday”. Two copies of this book from the British Library’s collection, as printed by one E.Tyler for book-seller Richard Royston, have been microfilmed, one as image set 199641 and one as image set 45789. Both copies are of the same book and therefore have the same identifier (T410) in Wing. Check ’em out at https://search.proquest.com/eebo/docview/2248511138 and https://search.proquest.com/eebo/docview/248511188 and see if you can tell them apart (I can’t, in this case) And yes, EEBO also has images of two different copies of the 1655 edition of this book: same author, title , and publisher, but completely different bibliographic entity, with a different Wing identifier (T409). And probably many others. He was big in the 17th century, that Jeremy Taylor.
A. Perhaps the primary key to the EEBO catalogue should be the image sets, since each catalogue entry concerns one set of images. However, given the choice, no-one would prefer a title like “microfilm no 42” to one like “amusing title of work”. Consequently, Proquest provides a unique identifier for each bibliographic work, which is suffixed with an image set identifier if there are multiple copies of the same work (which happens a lot), or if the work exists in multiple volumes which have been scanned separately (fortunately, less frequent). And, not to be outdone, TCP also provides a unique identifier, but in their case it identifies a specific copy of a specific work. The URLs I quoted above behave similarly: they uniquely identify a specific copy of a specific work.
Q. Wait, how many identifiers are there now?
A. Sticking with the 1668 third edition of Taylor’s XXV Sermons, we have two image sets (identifiers 45789 and 199641). Since these correspond with a single bibliographic entity, also known as Wing 610, Proquest gives them the same catalogue number (10772247). (You may wonder why they don’t just use the Wing number, unless you are a librarian). But we can’t have two entries in our catalogue with the same identifier, so Proquest appends the image set identifier to the catalogue number for one of them (I don’t know how they decide which, nor why they don’t do it for both). TCP, as noted above, just give each distinct item a distinct identifier: in this case the transcription of image set 45789 is in TCP text A64140, and the other is in TCP text B30404. All clear now?
Q. There must be an easier way of doing this
A. Yes. Amongst a raft (or maybe a coracle) of other improvements this year when Proquest moved the online access to EEBO to a new platform, they also introduced a new identifier called a “GOID”, which is essentially a unique number for every entry in the catalogue. That’s what I used in the URLs quoted above. Hoorah! We can now access anything in the EEBO catalogue using a simple numeric code, just like we can in the TCP subset of it.
Q. What about the TCP identifiers though?
A. Alas, these are currently not included in the dataset which underlies the Proquest online catalogue. As noted here earlier, I am working on a super TEI-compliant version of said dataset, and that will assuredly include the TCP identifiers. More on that anon.
My humble thanks to Paul Schaffner for patiently explaining all this to me. Any residual errors are mine, not his.