Collaborative working is increasingly popular, but it presents challenges due to the need for high responsiveness and disconnected work support. To address these challenges the data is optimistically replicated at the edges of the network, i.e. personal computers or mobile devices. This replication requires a merge mechanism that preserves the consistency and structure of the shared data subject to concurrent modifications. In this paper, we propose a generic design to ensure eventual consistency (every replica will eventually view the same data) and to maintain the specific constraints of the replicated data. Our layered design provides to the application engineer the complete control over system scalability and behavior of the replicated data in face of concurrent modifications. We show that our design allows replication of complex data types with acceptable performances.