Already in 1874 (hectographed edition) and 1886 (printed edition), Karl Franz Otto Dziatzko of the University Library at Breslau had presented a set of cataloging rules under the title "Instruction für die Ordnung der Titel im Alphabetischen Zettelkatalog der Königlichen und Universitäts-Bibliothek zu Breslau", also known as "Breslauer Instructionen" (English: Breslau instructions).
[4][5] Fritz Milkau [de], a later employee of Friedrich Althoff, played a decisive role in the creation of the PI.
During their time, the PI were a major step forward in the German library landscape and they were occasionally adopted also outside of Prussia.
In the case of library catalogs following keywords or correspondingly structured directories, knowledge of these rules is still helpful, however.
Also, historical holdings still exist in libraries which are organized in catalogs based on the PI system.