The concept of a "switching language " between different indexing languages and information retrieval systems has been discussed since the mid-1960s. Some preliminary investigates into the feasibility of switching between mediating tool yielded positive results. The Broad system of ordering(BSO) , a general classification scheme for information exchange and switching, has been under development as a joint FID/UNESCO project since 1973. The purpose of this study is to find out the origin, development, definition, and principle of BSO. The results of the study can be summarized as follows: (1) BSO is a switching language for the purpose of interconnection of information system which is located different regions, or using different indexing languages. (2) BSO is in effect, fully faceted and broad classification system. (3) BSO is not only a subject code but also an ordering system. (4) BSO can be used information retrieval system because the notation of composite subjects is formed by combining notation. (5) BSO has to some extent sacrificed brevity by leaving large unused notational gap for future use. (6) The structure of the scheme is in no way dependent upon the notation. notation.