Concept maps — creating overview of your permanent notes
The slipbox, or zettelkasten, method is one of the most widely recognized personal knowledge management systems (PKM). The zettelkasten method has a long history dating all the way back to the 15th century. The German sociologist Niklas Luhmann (1927–1998) is often mentioned as one of authors who attributed his huge output to his zettelkasten system. Luhmann wrote 50 books and around 550 articles — quite impressive!
In short, the analog version of the zettelkasten method operates with three types of notes.