1. A data storage and retrieval system for storing and retrieving a plurality of items of data, comprising: an input device for inputting items of variable data input; an output device for outputting items of data of said plurality of items; an indexed data memory unit including a general data memory unit and an associative index means operatively associated with said general data memory unit; wherein said general data memory unit comprises means for storing said plurality of items of data including a plurality of expressions for interrelating said items of data, said plurality of expressions including at least one mathematical expression and at least one logical expression, said plurality of items of data being arranged in classes of information corresponding to a plurality of levels of specificity and including a major class of information C.sub.1 and a plurality of classes of information C.sub.2,. .. , C.sub.N which are progressively more specific than said major class of information C.sub.1 said plurality of classes of information being arranged in a hierarchical structure wherein said major class of information and said plurality of classes of information are arranged in order of increasing specificity, each class of information having a plurality of members M.sub.1, M.sub.2,. .. , M.sub.i, and each member having at least one of said plurality of items of data; and wherein said associative index means comprises: (i) a first determining means for determining first indexes from said mathematical expression using said items of variable data input; (ii) a second determining means for determining second indexes from said logical expression using said items of variable data input and using said first indexes, said second determining means being in operative association with said first determining means, said second indexes determining a location of related items of data which are related to a chosen item of data for which said first and second indexes are determined; and (iii) means for selecting and retrieving said related items of data from a selected member of a class of information from said general data memory unit; and a data processing unit connected between said input device, said output device and said indexed data memory unit for controlling communication therebetween.