| 摘要 |
An application development system, optimized for authoring multimedia titles, enables its users to create selectively reusable object containers merely by defining links among instantiated objects. Employing a technique known as Hierarchical Encapsulation, the system automatically isolates the external dependencies of the object containers created by its users, thereby facilitating reusability of object containers and the objects they contain in other container environments. Authors create two basic types of objects: Elements, which are the key actors within an application, and Modifiers, which modify an Element's characteristics. The object containers (Elements and Behaviors-i.e., Modifier containers) created by authors spawn hierarchies of objects, including the Structural Hierarchy of Elements within Elements, and the Behavioral Hierarchy, within an Element, of Behaviors (and other Modifiers) within Behaviors. The system utilizes an Element's dual hierarchies to make that Element an environmental frame of reference to the objects it contains. Through techniques known as Hierarchical Message Broadcasting, Hierarchical Variable Scoping and Hierarchical Relative Positioning, objects automatically receive messages sent to their object container and access data known to their object container. An Element's position is even determined relative to the position of its parent Element container. The system is highly extensible through a Component API in which Modifiers and Services that support them can be added and integrated seamlessly into the system. The system's architecture is substantially platform-independent, automatically allowing most author's titles to run on multiple platforms. In addition, the entire authoring environment can be ported relatively easily to a variety of platforms due to the isolation a platform-dependent layer within the system. |
