Frameworks for Compound Documents Frameworks for Compound Active Documents (draft)

To provide a framework for component-based technology, we combine the bottom-up analysis of three specific systems with top-down conceptual models of interaction. CORBA/OpenDoc, COM/OLE/ ActiveX, and Java/JavaBeans concretely illustrate emerging principles of component and document design, such as the events-properties-methods model. They support components with visual, interactive listening membranes that transform black-box computers into glass-box systems whose “picture windows” allow clients to both see and modify what is inside. Frameworks are viewed as extensible collaborating collections of components with goal-directed behavior. Collaboration is conceptually modeled as a constraint on behavior just as collaboration among partners in a marriage or workers on an assembly line constrains the behavior of people. Interactive structure among objects and components is expressed by patterns, which are notoriously difficult to formalize, in large measure because they specify interactive systems that cannot be formalized by first-order logic. A constraint-based specification paradigm for components is introduced to express the collaborative semantics of frameworks. 1. Documents, Components, and Frameworks The concepts object, component, framework, document, and compound active document have contextdependent meanings but may, as a first approximation, be defined as follows: object: container with identity and interface operations that share a persistent state component: umbrella concept for variable granularity, reusable, possibly off-the-shelf entity framework: has collaborating components with goal-directed extensible behavior through an API document: component with visible interactive interfaces for browsing and authoring compound active document: document with autonomous parts programmable through scripting Components are an open-ended umbrella concept that include OpenDoc, COM, and JavaBeans components as well as off-the-shelf pluggable component-based software. Frameworks, the primary focus of this paper, are collections of collaborating components with domain-specific extensible client interfaces. Documents are specialized components whose visible interfaces support browsing and authoring, while compound active documents consist of parts with autonomous functionality supported by multiple threads and scripting. OpenDoc extends the file/folder desktop paradigm of the 1980s to provide a powerful and simple compound document model on top of CORBA’s interoperable distributed objects. ActiveX provides a document model for World Wide Web (WWW) documents on top of Microsoft’s COM/OLE. JavaBeans provides a Java-based application environment for managing components and building platforms out of beans (classes that conform to certain interface conventions) supplied in Java archive repositories (JARs). Comparison of OpenDoc, ActiveX, and JavaBeans document models yields principles for the design and implementation of frameworks of collaborative components with visible, interactive interfaces. OpenDoc, COM/OLE, and Java have very different component models. OpenDoc components have identity, a state, and visual interfaces, COM/OLE components consist of collections of interfaces that provide time-independent services and treat identity and state as properties of special state-sensitive interfaces for containers, monikers and data transfer, while Java components have a core interface and security model extended by modular class libraries and tools. OpenDoc specifies a language-independent infrastructure and document model from the ground up through an industry-wide effort coordinated by OMG. Its conceptual and architectural elegance provide a baseline for understanding document architectures, though it has been cancelled as a product. ActiveX spe-