The keyword system used is based on GEMET (GEneral Multilingual Environmental Thesaurus) - a thesaurus system developed for the European Topic Centre on Catalogue of Data Sources and the European Environment Agency. It contains over 5,000 keywords, organised in a hierarchical structure under 40 themes.
For this eLibrary, some additional keywords have been added to the GEMET to cater for some Namibian and southern African concepts that were not adequately covered.
Data sets in the eLibrary have been assigned the lowest level of keywords possible. This, together with a hierarchical structure, facilitates 'smart' searching. For example, searching on the broad term 'vertebrate' will automatically find any data set assigned the keyword 'bird', 'fish', 'mammal' etc or any subset of those keywords.
There are 40 top-level 'themes' which are then broken down into 'concepts' or keywords.