In Web-based Cooperative Information Systems (WCIS), user groups with different roles cooperate through specialized interfaces. Cooperative interaction and user interface structures are usually rather complicated, and modeling has an important part in them. Model-Driven Engineering (MDE) is a software engineering discipline which assists engineers in abstracting system implementations by means of models and metamodels. This article describes an interactive, structural metamodel for user interfaces based on component architectures as a way to abstract, model, simplify and facilitate implementation. The paper also presents a case study based on an Environmental Management Information Systems (EMIS), where three actors (a politician, a GIS expert, and a technician) cooperate in assessing natural disasters.