With the advent of the information society, many researchers are turning to artificial intelligence techniques to provide effective retrieval over large bodies of textual information. Yet any AI system requires a formalism for encoding its knowledge about the objects of its knowledge, the world, and the intelligence that it is designed to manifest. In the CODER system, the mission of which is to provide an environment for experiments in applying AI to information retrieval, that formalism is provided by a single well defined factual representation language. Designed as a flexible tool for retrieval research, the CODER factual representation language is a hybrid AI language involving a system of strong types for attribute values, a frame system, and a system of Prolog-like relational structures. Inheritance is enforced throughout, and the semantics of type subsumption and object matching formally defined. A collection of type and object managers called the knowledge administration complex implements this common language for storing knowledge and communicating it within the system. Of the three types of knowledge structures in the language, the frame facility has proven most useful in the retrieval domain. The factual representation language is implemented in Prolog as a set of predicates accessible to all system modules. Each level of knowledge representation (elementary primitives, frames, and relations) has a type manager; the frame and relation levels also have object managers. Storage of complete knowledge objects (statements in the factual representation language) is supported by a system or external knowledge bases. One paper discusses the frame construct itself, the implementation of the knowledge administration complex and external knowledge bases. and the use of the construct in retrieval research. The paper closes with a discussion of the utility of the language in experiments.