Species catalogs—printed or digital—are a specific form of encyclopedias and compendia. They are designed for different purposes, and "are among the most useful aids to the taxonomist" (Mayr et al., 1953) and, as Michael Ohl argues, for many other disciplines as well. The backbone of what Michael Ohl understands as a "species catalog" is formed of the names of species and higher taxa, which are usually arranged in a classification. In some catalogs the names are arranged alphabetically and in some others according to multiple criteria. In most catalogs, varying amounts of supplementary information is added to the each species name, but many are pure lists of names. In its most simple form, species catalogs take the shape of a dictionary as a structured collection of words. However, the fact that those species compendia are rather referred to as catalogs emphasizes their function not as compendia of words but as compendia for the underlying information, to which the names refer. Although catalogs have usually been seen as documenting or archiving, hence, technical tools, they have undoubtedly played a significant role as references to existing knowledge about "what there is" in the living world (Ogilvier, 2006; Daston, 2012; Sepkoski, 2013).
The core of evolutionary and systematic biology is comparative, and thus catalogs can significantly contribute to setting up research agendas by selecting research targets out of a (theoretically) complete compilation of possible target species. Besides, one of the most important roles of species catalogs is to summarize knowledge in the taxonomic exploration of the living world. In this context, the perfect catalog provides total coverage of the world it describes. This is already an inherent property of any classification (Bowker and Star, 1999), but the "dream of completeness" is probably a significant factor in developing large-scale
In a modern context, the printed catalog as a structured information technology is closely connected to digital databases, which are able to organize large amounts of data more efficiently and faster. However, its function as a compendium of names as the reference points to a diverse set of further information has not changed significantly. As a "memory practice" (Bowker, 2005), the simple list and the complex database as "dispositifs techniques" (Foucault, 1973) work in a very similar way as language based knowledge memory tools. In his project, Michael Ohl focused on major historical and recent cataloging initiatives in zoology with a global perspective.