design patterns satzinger, jackson, and burd object-orieneted analysis & design
Post on 21-Dec-2015
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Summary SlideSummary Slide
Importance of Design Patterns Basic Design Patterns Designing Enterprise-level Systems Differences between client/server and Internet systems UML Notation for Deployment Diagrams Simple Internet Architecture Two-layer Architecture Three-layer Architecture Web Services
Importance of Design PatternsImportance of Design Patterns
Standard design templates can speed OO design Patterns can exist at different levels of abstraction
– At the most concrete level, a class definition with code– At the most abstract level, an approach to a problem
Patterns should contain five main elements– Pattern name, problem, solution, example, benefits and consequences
Basic Design PatternsBasic Design Patterns The authors of Elements of Reusable Object-Oriented Software
(referred to as the Gang of Four) developed a basic classification scheme for patterns
The 23 GoF patterns are some of the most fundamental and important patterns in use
Scores of other patterns have been defined– For example, both Java and .NET have sets of enterprise patterns
Singleton PatternSingleton Pattern For classes that must have only one instance, but need to be
invoked from several classes and locations within the system The class itself controls the creation of only one instance
– A static variable of the class refers to the object that is created – A class method instantiates the object on the first call, and returns a
reference to the object on subsequent calls
Adaptor PatternAdaptor Pattern
Plugs an external class into a system– Converts the method calls from within the system to match the method
names in the external class
A standard solution for protection from variations– Insulates the system from frequently changing classes
An interface is frequently used to specify and enforce the use of correct method names
Observer patternObserver pattern
Used to handle event-processing and reduce coupling The domain class
– Allows other classes to “subscribe” as listeners– “Publishes” the changes to the listeners
The windows class – Sends a reference of itself to subscribe as a listener– Implements the method to be invoked when notified
Inherits the method from the listener interface
Designing Enterprise-level SystemsDesigning Enterprise-level Systems
Enterprise-level systems share components among multiple people or groups in an organization
Enterprise-level systems almost always use multiple tiers of computers
Can be client/server network-based or Internet based Designed with deployment diagrams
– A type of implementation diagram that shows physical components across different locations
Differences between client/server and Internet Differences between client/server and Internet systemssystems
UML Notation for Deployment DiagramsUML Notation for Deployment Diagrams
Component– Executable module or program– Has an application program interface (API) that is available to the outside
world Node
– A physical entity at a specific location Frameset
– A high-level object that holds items to be displayed by a browser
Simple Internet ArchitectureSimple Internet Architecture Used for viewing static information The browser component executes on the client computer The Internet server component executes on the server computer Pages reside on the server and are sent to the browser for display Program logic is inserted through scripting languages, applets, or
other controls
Two-layer ArchitectureTwo-layer Architecture
Primarily captures information from the user and updates the database
The domain layer and data access layer are usually combined Input data is sent to a CGI or an application server The user-interface classes often contain the business logic and
data access– Processing takes place with servlets (Java) or code behind classes
(.NET)
Three-layer ArchitectureThree-layer Architecture
Separates domain layer and data access layers Necessary for systems with complex business logic or multiple
user interfaces Using CGI
– Provide a use case controller for each form
Using an application server– Java tools: Java Server Pages and servlets– .NET tools: Common Runtime Language and code behind classes
Web ServicesWeb Services
A program that provides a service via the Internet The service is posted in a directory so that systems can find it
– Requests for information go to the UDDI directory– UDDI provides the Internet address of a program offering that service– The application then requests the information
All communication is based on XML to allow for generic data exchange