The Lexicon is a set of preferred terms, alternative terms and illegal terms, compiled to control data entry for certain fields, and to focus searches on those fields. It is not a haven for creative writers and free spirits. At its best the Lexicon is a tool to control vocabulary according to hierarchies determined by standard authorities. This organization of "allowed" terms and "not allowed" terms controls data entry to facilitate efficient searches. At its worst, the Lexicon can defeat its own purpose. If necessary terms haven't been added or organized, the Lexicon can limit data collection and retrieval. If cataloguers, data entry personnel or users don't have adequate training, all the organization in the world won't make the data accessible.

The Lexicon is a separate module/table in the ARGUS program and is linked to the other modules/tables wherever there are superfields designated as Lexicon-controlled.

Lexicon-controlled fields are different from term-controlled fields. Term-controlled fields have a drop-down box attached. The drop-down contains a flat list of terms from which you can choose a term to use. Lexicon-controlled fields are linked to the Lexicon, and when you are entering data or searching, you can look in the Lexicon for terms to use in that field. The Lexicon is not a flat list, but a hierarchically structured set of terms, and the hierarchy is used when searching.

Both term-controlled fields and Lexicon-controlled fields are designed to make searching more efficient, through the use of vocabulary control.