Appendix A: Pattlets

Pattlets are actual patterns to which this guide refers, but which it does not discuss in detail. For more information about why pattlets are used, see Chapter 2, “Organizing Patterns.” The following table lists each pattlet mentioned in this guide and, where applicable, a reference to the original work that identified it.

Table A: Pattlets

Pattlet	Solution	Reference
Four-Tiered Distribution	Refines Three-Tiered Distribution by separating the Web servers into their own tier.	Microsoft PAG (TBD)
Abstract Factory	Provides an interface for creating families of dependent objects without specifying their concrete classes.	Gamma95
Adapter	Converts the interface of a class into another interface clients expect.	Gamma95
Application Controller	Is a centralized point for handing screen navigation and the flow of an application.	Fowler03
Application Server	An execution environment for enterprise applications. For developers, application servers provide an integrated set of core technical services and high-level frame-works. For administrators, application servers provide integrated management, operations, and deployment services and tools.	Microsoft PAG (TBD)
Pattlet	Solution	Reference
Assembler	An instance of the Mapper [Fowler03] pattern Fowler’s discussion of the Data Transfer Object (DTO) pattern talks about using an assembler object to populate the DTO with data.	Fowler03
Bound Data Control	Dynamically binds a presentation or view component directly to the data it is presenting.	Microsoft PAG (TBD)
Bridge	Decouples an abstraction from its implementation so that the two can vary independently.	Gamma95
Command(s)	Encapsulates a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.	Gamma95
Decorator	Attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.	Gamma95
Facade	Provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.	Gamma95
Gateway	An object that encapsulates access to an external system or resource.	Fowler03
Implementing Data Transfer Object in .NET with Serialized Objects	Discusses implementation of Data Transfer Object using a .NET serialized object.	Microsoft PAG (TBD)
Layer Supertype	A type that acts as the supertype for all types in its layer.	Fowler03
Layers	Structures applications that can be decomposed into groups of subtasks in which each group of subtasks is at a particular level of abstraction.	Buschmann96
Mapper	An object that sets up a communication between two independent objects.	Fowler03
Pattlet	Solution	Reference
Mediator	Defines an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently.	Gamma95
MonoState	Similar to Singleton but focuses on state rather than identity. Instead of controlling the instances of an object, MonoState ensures that there is only one shared state for all instances by declaring all data members static.	Martin02
Observer	Defines a one-to-many dependency between objects so that when one objects changes state, all its dependents are notified and updated automatically.	Gamma95
Naming Service	A well-known repository that maps external names to specific objects.	Mowbray97
Page Data Caching	An alternative to page caching that caches the data on which a page depends instead of caching the whole page (data plus content).	Microsoft PAG (TBD)
Page Fragment Caching	A refinement of Page Cache, where each page is composed of fragments and caching is controlled at the fragment level.	Microsoft PAG (TBD)
Presentation-Abstraction- Controller	Defines a structure for interactive software systems in the form of a hierarchy of cooperating agents. Every agent is responsible for a specific aspect of the application’s functionality and consists of three components: presentation, abstraction, and control. This subdivision separates the human-computer interaction aspects of the agent from its functional core and its communications with other agents.	Buschmann96
Proxy	Provides a surrogate or placeholder for another object to control access to it.	Gamma95
Pattlet	Solution	Reference
Remote Facade	Provides a coarse-grained facade on fine- grained objects to improve efficiency over a network.	Fowler03
Server Farm	A set of servers that are fed requests from a load balancer.	Microsoft PAG/CIS (TBD)
Special Case	A subclass that provides special behavior for particular cases.	Fowler03
Strategy	Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.	Gamma95
Table Data Gateway	An object that acts as a Gateway to a database table. One instance handles all the rows in the table.	Fowler03
Table Module	A single instance that handles the business logic for all rows in a database table or view.	Fowler03
Template Method	Defines the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.	Gamma95
Utility Component	A component that provides a commonly used low-level service such as persistence, logging, or lookup.	Microsoft PAG (TBD)