Present day shortcomings in information retrieval are the results of a failure to properly contend with the problem of data representation. The index provides the necessary linkage between a multiplicity of sources and a single receiver. Whether considering the source/document-space interface or the query/index interface, the elements of the underlying communication phenomena are the same: sets of documents, sets of attributes, and sets of relations expressing a connection between documents and attributes. The essential operation of the indexing system is the creation of a representation of the document space. The analysis -- document transformations and the final index-query transformations are shown to be, respectively, a prerequisite to, and function of, the document space representation. The operating characteristics of the indexing system are modeled by means of the index space. From a different point of view, the concept of error, organization, information and search are introduced through a consideration of the indexing process as a thermodynamic system. Thus, indexing is viewed as an order-increasing operation that identifies common data elements and relations between data elements present in the input document stream. (Author/MM)