Two types of approach are possible for construction of object-oriented application systems : one is to identify a set of objects on the basis of a predefined problem solving framework, and the other is to design and implement a framework within given objects. Following the former methodology, we designed a framework for language processing in a speech understanding system, and then realized it as ASP (an association-based parser). Previous object-oriented language processing systems have emphasized their object-oriented representation of linguistic knowledge. But, in the case of speech understanding, control knowledge also plays a crucial role, where ambiguities are increased drastically by acoustic-phonetic errors as well as homonyms. In ASP, not only linguistic knowledge but also control knowledge is modularized into classes. This makes it easy for developers to realize various control strategies in ASP. ASP has been implemented on a Symbolics Lisp machine using Flavors, and almost 2O00 classes are involved. In particular, to enhance the extensibility of its knowledge base, ASP exploits layered software architecture, which assumes different types of programming skill for each layer. Currently, ASP is in operation as a language processing subsystem of a speech understanding system SPURT-I, and its performance has been evaluated with a 1O0O-word vocabulary. This paper gives a brief description of the framework of ASP, then explains its object-oriented implementation. The programming environment is discussed in terms of its extensibility, and the right level of object-oriented programming paradigm is clarified.