Architecture constraints are specifications which enable developers to formalize design rules that architectures should respect, like the topological conditions of a given architecture pattern or style. These constraints can serve as a documentation to better understand an existing architecture description , or can serve as invariants that can be checked after the application of an architecture change to see whether design rules still hold. Like any specifications , architecture constraints are frequently subject to reuse. Besides, these constraints are specified and checked during architecture design time, when component descriptions are specified (or selected from repositories), then instantiated and connected together to define architecture descriptions. These two facts (being subject to reuse and instantiation/connection) make architecture constraints good candidates for component-based design within a unified environment. In this paper, we propose a component model for specifying architecture constraints. This model has been implemented as an extension to an ADL that we have developed, which is called CLACS. The obtained process advocates the idea of specifying architecture constraints using the same paradigm (of component-based development) as for architecture description. To evaluate the component model, we conducted an experiment with a catalog of constraints formalizing the topological conditions of architecture patterns. The results of this experiment showed that constraint specification is improved by this reuse-by-composition model.