Archetypes, Color, and the Domain-Neutral ... - Petercoad.com

Archetypes, Color, and the Domain-Neutral Component ▼ 25Plug-in component connections:each component has plug-in points,eliminating needing to know the class(es)of objects it might connect to.ProductSaleProductSaleIProductSaleShipmentShipmentIShipmentinterfaceIProductSaledoesDateMeetDueDate0..*ShipmentassessTimelinesswasShippedBeforeDueDateProductSaleassessTimelinessOfIShipmentsdoesDateMeetDueDate0..*interfaceIShipmentassessTimelinessFIGURE 1-23. ▲ Plug-in connectivity.Now consider plug-in connectivity. An object interacts with whateveris plugged into a plug-in point (Figure 1-23).A product sale holds a collection of objects from classes that implementthe IShipment interface. A shipment holds a collection of objectsfrom classes that implement the IProductSale interface. It really does notmatter which classes the connecting objects are in, only that the interfacemust be implemented.We can ask a product sale to assess the timeliness of its shipments;it interacts with its IShipment implementers, whatever is plugged intothat plug-in point (Figure 1-24).And we can ask a shipment if it was shipped before the due dates forits corresponding product sales; it interacts with its IProductSale implementers,whatever is plugged into that plug-in point (Figure 1-25).For modeling simplicity, we build models with direct connections.Then we choose where we want flexibility and add plug-in connectivity(like deciding where we want sockets on a circuit board; it’s a decision inadding flexibility).1.8 TWELVE COMPOUND COMPONENTSWhat if you had a substantial collection of enterprise-component models?Each component would establish a fundamental model shape, themost common responsibilities for the classes and interfaces, and the pluginpoints for extending capabilities. Each component would give yourmodeling team something more than a blank whiteboard for gettingstarted in building a model for your application or family of applications.