The query layer is a C++ program which mediates between the interface layer and the two database search engines, maintaining the ``state'' of the search and managing the data objects which represent the query as it changes throughout a session. It also carries out subsidiary tasks such as transaction logging. Although built specifically for the ENQUIRE project, it supports certain functions which have not been exploited within the current interface, and has a potential for configurability in terms of, for example, the type of database accessed, the query formulation methods used, and whether the user interface is graphical or character-based.
Details of some of the algorithms implemented within the query layer are given in section 2.3 below.