Software Design Patterns

The standard participants in the Proxy design pattern are Proxy, Subject, and RealSubject. ConcreteProxy is not a standard role or participant name defined in the Gang of Four design patterns specification.

The classic Gang of Four State design pattern consists of three core participants: Context, State, and ConcreteState. Context defines the client interface, State defines the common state interface, and ConcreteState implements state-specific behaviors. ConcreteContext is a fictional role and is not part of this pattern.

The Iterator design pattern provides a way to access elements of an aggregate object (collection) sequentially without exposing its underlying representation. It abstracts the traversal logic and allows different traversal strategies. Visitor separates operations from object structure, Composite builds tree structures, and Command encapsulates requests as objects.

The Factory Method pattern defines an interface for creating an object but lets subclasses decide which class to instantiate. It defers instantiation to subclasses, allowing a class to delegate instantiation to child classes. Abstract Factory creates families of related objects, Builder constructs complex objects step-by-step, and Prototype clones existing objects.

The Template Method pattern defines the skeleton of an algorithm in a base class, allowing subclasses to override specific steps without changing the overall structure. This promotes code reuse and ensures the algorithm's invariant steps remain consistent while enabling customization of variable steps. Chain of Responsibility handles request passing through a chain, Interpreter interprets grammar, and Mediator centralizes communication between objects.

The Bridge pattern separates abstraction from implementation, allowing them to vary independently. JMS acts as a bridge between the Order Entry application and various subsystems by providing a messaging layer that decouples the producer from consumers. Observer is about one-to-many dependencies, Mediator centralizes communication, Adapter converts interfaces, and Visitor separates operations from object structure.

The Application Controller centralizes control and retrieval logic for view and command processing, managing the flow of control and coordinating interactions between different components. Front Controller handles all requests but focuses more on request routing, Context Object encapsulates protocol-specific data, and Business Delegate reduces coupling between presentation and business tiers.

The Business Delegate pattern reduces coupling between the presentation tier and business tier by providing a simple entry point for accessing remote business services. It acts as a facade that hides the complexity of looking up and accessing business components. Application Controller manages flow control, Front Controller handles request routing, and Dispatcher View is a view management pattern.

The Data Access Object (DAO) pattern encapsulates all data access logic, providing a clean separation between business logic and data persistence. It enables loose coupling by abstracting the underlying data source and providing CRUD operations. Service Activator enables async processing, Domain Store handles transparent persistence, and Business Object represents business entities.

The Service Activator pattern enables asynchronous processing by receiving messages from JMS and invoking business services in a separate thread or process. It decouples message reception from business logic processing. DAO handles data access, Domain Store provides transparent persistence, and Business Object represents business entities.

The Session Facade simplifies client access to business tier components by providing a unified interface that aggregates multiple business objects. It eliminates the client's need to interact with multiple fine-grained business components directly. Service Locator finds and creates services, Application Service provides business logic, and Business Delegate reduces tier coupling.

The Domain Store pattern provides transparent persistence for an object model by abstracting the mapping between objects and their persistent storage. It handles the complexity of saving, loading, and managing object state without exposing persistence details to business logic. Web Service Broker exposes business services as web services, DAO provides data access operations, and Service Activator enables async processing.

The Value List Handler pattern uses the Iterator pattern to provide query execution and result processing services, especially for large result sets. It allows clients to process data incrementally without loading everything into memory. Transfer Object carries data across tiers, Composite Entity represents coarse-grained entities, and TO Assembler constructs transfer objects.

The Web Service Broker pattern is applicable when you need to bridge the gap between business requirements and existing service capabilities, exposing business logic as web services. It facilitates service integration and reuse. Entity beans are a persistence concern, web container is a deployment environment, and sophisticated business logic describes domain complexity rather than service bridging.

The Business Delegate pattern benefits include reducing coupling between tiers, adding a uniform interface for clients, and improving performance through caching. However, it DOES add an additional layer to manage - this is often cited as a potential drawback rather than a benefit. Option B correctly identifies this as NOT being a benefit.