Melvil Dewey published his decimal classification in 1876, the same decade the card catalogue became standard American library furniture. A card per book, drawers per subject, guide cards per letter — a physical index that could be edited one card at a time without reprinting anything. It looks primitive next to a search bar, but it solved a real problem: how do you let a stranger, with no training, find something in a collection they've never seen?
The union catalogue and the API
By the mid-twentieth century, libraries were sharing catalogue records between institutions — a union catalogue, letting one library's index describe another library's shelf. This is functionally identical to an API: a standard record format (MARC, in the library case) that lets one system describe data it doesn't own. Long before "interoperability" was a product requirement, it was a cataloguing committee's entire job.
Keyword search and its discontents
Full-text search replaced controlled vocabulary with statistics: instead of a librarian deciding which subject headings apply, an algorithm ranks documents by word frequency and link structure. It is faster and needs no training. It is also why search results reward whoever uses your exact words, rather than whoever actually answers your question — a trade the card catalogue never had to make, because a human indexer stood between the question and the shelf.
Every card catalogue was a compromise between what a book is about and what a person will type.
The search bar didn't invent that compromise. It just removed the person who used to negotiate it on your behalf.