The paper presents an approach to a memory structure of design ideas in a library of design precedents. A model of case memory for design is developed. The model is composed of distinct chunks of knowledge called design stories. A formalism for the design story is proposed which represents the linkage between design issue, concept and form in stories. Stories are structured in memory according to a semantic network. The lexicon of the semantic network acts as a memory index. The memory structure and indexing system are demonstrated to enhance search and to support crosscontextual browsing and exploration in the precedent library. The approach is demonstrated in a pilot design aid system in the task domain of early conceptual design in architecture.