When a new book arrives, it will acquire a number and/or label in several forms: The ISBN will be somewhere on the book itself. We enter the accession number into the system when an item enters the collection. A barcode might be added for circulation, and the call number will be on the spine label. These can all look the same at first glance, but each number has a different meaning to keep in mind when interpreting catalog records and preventing mistakes with shelving, circulation, inventory, and item pickup.
The ISBN is the book’s identity: It is associated with the publication as a whole, not with an individual copy owned by a library. If a title is issued simultaneously in hardcover and softcover, there will be different ISBNs for those two editions, and all the copies of one of those editions will share an ISBN. So, you can’t assume there is a 1:1 ratio between the ISBN and the number of items on a shelf, or between the ISBN and the number of different volumes we hold. Rather, it can be used to verify bibliographic data.
An accession number associates with the physical arrival of a specific item in a collection. It might be created when a title is entered into an accession book or other collection register. Local practice varies on whether you also document the accession date, source, cost, title and/or other subject, and collection status. In short, unlike the ISBN, it belongs to the library, and two copies of a book can share an ISBN while the library assigns a unique accession number to each for its own records.
The barcode is associated with an item, too, but usually it serves circulation functions as a quick way to find a circulation record for check-out, check-in, renewal, inventory, or status change. It generally doesn’t help someone find a shelf location for a book. It connects circulation data for a physical copy to circulation records in a library catalog, a database, or a paper record. So if a barcode has been damaged, it could lead to one book being in the catalog and another in a person’s scanner. This is why you check that the barcode and item record always correspond.
The call number is the shelf location. It can contain the classification number combined with letters, numbers, or symbols representing an author, title, or local subject or collection. It appears in the library catalog and sometimes also on the spine label, so the user can move from a list of results for a given topic in the catalog to a location on the bookshelves. Shelving a book alphabetically by title will break the sequence of the collection if it is arranged, for instance, first by class subject, then by author mark. When doing shelf reading (shelf matching), the call numbers of every label in one section should be compared to those of the call numbers of the books you just pulled.
Pick three books, pull up the catalog, and make a chart or table. Write down the ISBN of the book and the accession number on an item record. Next, note the barcode on the book. Add the call number from the catalog or the spine label. Now you’ll have four pieces of data for each title. Write a sentence in the column describing what the number is for. Check for two copies of the same book; do they have the same ISBN? Every physical book? The accession number on the item record. The barcode? The call number? This activity is not about memorizing a definition of what any of these numbers means; rather, the point of using real examples is to keep the connections between publication data, acquisition item records, circulation records, and shelf location fresh in mind, and not to confuse one with another.