Nowadays, adaptive web sites must have the ability to use distributed repositories. The variety of available data sources and user profiles quickly lead to a combinatorial explosion of web site versions. It is impossible to manage these web sites without some form of automation. We are interested in web sites for which users belong to a kind of community of practices: they share a common knowledge to work together. We claim that the explicit knowledge of communities is the key issue to automate the hypermedia generation and thus to ensure consistency and comprehension. We have designed a flexible adaptive composition engine. In our framework, hypermedia consistency is managed by an author through content, adaptation and sites structure at knowledge level and based on his know-how. Our major contribution consists of: (i) a semantic organization of resources, (ii) a declarative specification of adaptation and (iii) the flexibility of the composition engine.