Methods and apparatus, including computer program products, related to extensibility of pattern components in a visual modeling language environment. A pattern component may implement an interface, the pattern component may be received (e.g., by a compiler), and a determination may be made as to whether components of the interface are implemented by the pattern component. If so, a reference to the interface is bound to the pattern component (e.g., a function call referencing a function signature of an interface may be substituted with a call to a function having the same name of the pattern component). A role may be assigned to a pattern component of a visual modeling environment of an application development system and a behavior may be performed based on the role assigned to the pattern component.