Schlagwortkatalog or SWK (English: Keyword catalog) is a German word for a library catalog that lists the publications according to descriptor keywords and thus allows selective thematic searches for literature. A keyword is understood to be a natural language expression that reproduces the content of the publication as briefly but precisely as possible. Complex content can be described using a syntactical keyword chain, a combination of several individual keywords (example: Uganda / child / soldier / experience report).[1] The sub-keywords are not only used for targeted research, but also allow catalog users to see whether the document found is relevant to their search. While earlier keyword catalogs were kept as an independent card catalog, the search option for keywords is integrated in modern OPACs.