Answer

Books, Journals, and digital resources are given unique numbers that can be used to identify them and make finding them easier.

E-resources/digital resources

• DOI (Digital Object Identifier) or a PMID (PubMed Identifier) is a unique number that has been assigned to a digital object, such as an article, book chapter, or data set.

If you have the DOI or PMID for something, it can help you get directly to the content.

Journals

• ISSN stands for International Standard Serial Number. ISSN's have eight digits, and each is unique to a journal publication.

Books

• ISBN stands for International Standard Book Number. ISBN's have 10 or 13 digits, and each is unique to a book publication.