For some research the book form is just not conducive to the most productive work. Both the experiences of Beatrice Webb (My Apprenticeship, Appendix C) and Adolph Erman (on Wb) show that database forms for sorting, filtering, and comparing have been highly productive and provide a wealth of information which simply couldn't be done otherwise.

In the early twentieth century one might have created a card index to study a large textual corpus, but in the twenty first one is more likely to rely on a relational database instead.

Seems like from a historical perspective hierarchical databases were more prevalent in the 1960s and relational databases didn't exist until the 1970s. (check references for this historically)

Of course one must consider that within a card index or zettelkasten the ideas of both could have co-existed in essence even if they weren't named as such. Some of the business use cases as early as 1903 (earlier?) would have shown the idea of multiple storage and relational database usage. Beatrice Webb's usage of her notes in a database-like way may have indicated this as well.