Most current approaches to object-oriented reusability are based on empirical methods. However, the formal specification of reusable components and the development of a rigorous method for their systematic reuse permit building "correct" and efficient object-oriented software.This paper proposes the SRI model for the definition of the structure of a reusable component. This model integrates algebraic specifications and concrete classes in an object oriented language. A rigorous method for retrieval, adaptation and integration of SRI components is described.Eiffel was chosen as the language to demonstrate the power of the model. In such a framework, an Eiffel application is produced semiautomatically from previously existing classes by applying specification building operators for extension, renaming, restriction and composition.