Matadata Mapping
Query Object
Repository
Wednesday, October 10, 2007
Object Relational Structural Patterns
Identity Field
Foreign Key Mapping
Association Table Mapping
Dependent Mapping
Embedded Value
Serialized LOB
Single Table Inheritance
Class Table Inheritance
Concrete Table Inheritance
Inheritance Mappers
Foreign Key Mapping
Association Table Mapping
Dependent Mapping
Embedded Value
Serialized LOB
Single Table Inheritance
Class Table Inheritance
Concrete Table Inheritance
Inheritance Mappers
Offline Concurrency Patterns
Optimistic Offline Lock ( by David Rice)
Pessimistic Offline Lock ( by David Rice)
Ciarse-Grained Lock ( by David Rice and Matt Foemmel)
Implicit Lock ( by David Rice)
Pessimistic Offline Lock ( by David Rice)
Ciarse-Grained Lock ( by David Rice and Matt Foemmel)
Implicit Lock ( by David Rice)
Web Presentation Patterns
MVC - Model View Controller
Page Controller
Front Controller
Template View
Transform View
Two Step View
Application Controller
Page Controller
Front Controller
Template View
Transform View
Two Step View
Application Controller
Tuesday, October 09, 2007
Book: Patterns of Enterprise Application Architecture (PoEAA).
link for few more books by him
http://martinfowler.com/books.html
http://martinfowler.com/books.html
Tuesday, October 02, 2007
Application Frameworks
Why Use an Application Framework?
There are five major benefits of using application frameworks: Modularity, Reusability, Extensibility, Simplicity, and Maintainability.
Modularity
Modularity, the division of an application into structural components, or modules, allows developers to use the application framework in a piece-by-piece fashion. Developers who want to use one component of the application framework are shielded from potential changes to other parts of the framework. As they build applications on top of the framework, their development is better insulated from changes occurring in other parts of the application framework, resulting in a significant boost to their productivity and a reduction in the amount of time spent on fixing code affected by other parts of the application. By dividing the framework into modules, we can maximize productivity by assigning a developer the specific part of the application that would benefit most from that developer's expertise. The advantage that accrues from modularity can be seen, for example, in Web applications: developers who are expert in presentation user interfaces can be more productive when assigned to the front-end portion of the application, while developers who are expert in the development of application business logic can be more productive when assigned to the middle tier and back-end portion of the application. Similarly, developers can leverage the framework module related to the user interface during their development of the presentation tier of the application, while other developers can leverage the framework module related to the development of business objects during their development of the middle and back-end tiers of the application.
Reusability
Reusability of code is one of the most important and desirable goals of application development. An application framework provides such reusability to the application built on top of it not only by sharing its classes and code, but by sharing its designs as well. Applications usually contain many tasks that are similar in nature. However, different developers on the team often create their own implementations of these similar tasks. The result of such duplicated implementation is not only the unnecessary waste of resources on the duplicated code, but also the problem of maintainability further down the road, since any change to the task must be duplicated in multiple places throughout the application to ensure its integrity. On top of that, each developer might use a different design approach during implementation. This opens the application to risks of poor software design, which could lead to unforeseen issues down the road. With an application framework, however, we can move much of the duplicated code and commonly used solutions from the application layer to the framework components. This reduces the amount of duplicate code developers have to write and maintain, and significantly boosts their productivity. The application framework is also the place where we can bake many well-tested software designs into the components. Developers may not always be experts in software design, yet as they start using these framework components to build their applications, they unavoidably reuse many good software design approaches, such as design patterns that underlie the framework components.
Extensibility
Extensibility, the ability to add custom functionalities to the existing framework, allows developers not only to use the framework component "out of the box," but also to alter the components to suit a specific business scenario. Extensibility is an important feature for the framework. Each business application is unique in its business requirements, architecture, and implementation. It is impossible for a framework to accommodate such variation by itself, but if a framework is designed in such way that it leaves room for some customization, then different business applications can still use the generic features of the framework, yet at the same time developers will have the freedom to tailor their applications to the unique business requirements by plugging the customized logic into the framework. With a high degree of extensibility, the framework itself can become more applicable to different types of business applications. However, in creating a framework, its extensibility should always be determined in the context and assumptions of the application you are trying to develop. Each time you increase the extensibility of the framework, your developers may need to write more code and require more detailed knowledge about how the framework operates, which will have a negative impact on their productivity. An extreme scenario of a highly extensible framework is Microsoft's .NET framework itself, which is designed for development of a wide variety of applications. Indeed, there are few constraints in developing applications using the .NET framework, but as a result, you lose the benefits of what an application framework can provide. The key is to add the flexibility and extensibility to the places in the framework that are more likely to change in the particular type of application you are developing.
Simplicity
The term "simplicity" here means more than just being simple. Simplicity refers to the way the framework simplifies development by encapsulating much of the control of process flow and hiding it from the developers. Such encapsulation also represents one of the distinctions between a framework and a class library. A class library consists of a number of ready-to-use components that developers can use to build an application. However, developers must understand the relationships between various components and write process flow code to wire many components together in the application. On the other hand, a framework encapsulates the control of such process flow by prewiring many of its components so that developers do not have to write code to control how the various components interact with each other.
Maintainability
Maintainability, the ability to effectively support changes to the application as a result of changes to the business requirements, is a welcome side effect of code reuse. Framework components are commonly shared by multiple applications and multiple areas within a single application. Having a single copy of the framework code base makes the application easy to maintain, because you need to make a change only once when a requirement changes. The application framework may also contain many layers. Each layer makes certain assumptions about the business the application is intended to serve. The bottom layer consists of framework components that make no assumptions about the business. They are also the most generic components in the framework. As you move higher up the stack of the layers, its components depend on more business assumptions than do the previous layers, and hence are more susceptible to change when business requirements and rules change. When changes do occur, only the components at the layer where the business assumption is broken need to be fixed and tested. Therefore, by injecting different levels of business knowledge into different levels of the framework layers, you can reduce the cascade effect of changing business rules and requirements to the application. This also leads to the reduction of maintenance costs, since you need to touch only the code that is affected by the business rule change
To better understand how we can develop an application framework, we need first to understand what goes in an application framework and its relationship to other parts of the system.
Framework Layers
Framework Development Techniques
In order to develop an effective application framework, you need to know some common techniques for framework development. The following list shows some useful techniques and approaches that can help you develop a framework that is both easy to use and extensible.
Common spots
Hot spots
Black-box framework
White-box framework
Gray-box framework
Design patterns
Common spots, hot spots, and design patterns are some of the techniques used in framework development. Black, white, and gray boxes represent the approaches you can take to developing the framework.
.........
There are five major benefits of using application frameworks: Modularity, Reusability, Extensibility, Simplicity, and Maintainability.
Modularity
Modularity, the division of an application into structural components, or modules, allows developers to use the application framework in a piece-by-piece fashion. Developers who want to use one component of the application framework are shielded from potential changes to other parts of the framework. As they build applications on top of the framework, their development is better insulated from changes occurring in other parts of the application framework, resulting in a significant boost to their productivity and a reduction in the amount of time spent on fixing code affected by other parts of the application. By dividing the framework into modules, we can maximize productivity by assigning a developer the specific part of the application that would benefit most from that developer's expertise. The advantage that accrues from modularity can be seen, for example, in Web applications: developers who are expert in presentation user interfaces can be more productive when assigned to the front-end portion of the application, while developers who are expert in the development of application business logic can be more productive when assigned to the middle tier and back-end portion of the application. Similarly, developers can leverage the framework module related to the user interface during their development of the presentation tier of the application, while other developers can leverage the framework module related to the development of business objects during their development of the middle and back-end tiers of the application.
Reusability
Reusability of code is one of the most important and desirable goals of application development. An application framework provides such reusability to the application built on top of it not only by sharing its classes and code, but by sharing its designs as well. Applications usually contain many tasks that are similar in nature. However, different developers on the team often create their own implementations of these similar tasks. The result of such duplicated implementation is not only the unnecessary waste of resources on the duplicated code, but also the problem of maintainability further down the road, since any change to the task must be duplicated in multiple places throughout the application to ensure its integrity. On top of that, each developer might use a different design approach during implementation. This opens the application to risks of poor software design, which could lead to unforeseen issues down the road. With an application framework, however, we can move much of the duplicated code and commonly used solutions from the application layer to the framework components. This reduces the amount of duplicate code developers have to write and maintain, and significantly boosts their productivity. The application framework is also the place where we can bake many well-tested software designs into the components. Developers may not always be experts in software design, yet as they start using these framework components to build their applications, they unavoidably reuse many good software design approaches, such as design patterns that underlie the framework components.
Extensibility
Extensibility, the ability to add custom functionalities to the existing framework, allows developers not only to use the framework component "out of the box," but also to alter the components to suit a specific business scenario. Extensibility is an important feature for the framework. Each business application is unique in its business requirements, architecture, and implementation. It is impossible for a framework to accommodate such variation by itself, but if a framework is designed in such way that it leaves room for some customization, then different business applications can still use the generic features of the framework, yet at the same time developers will have the freedom to tailor their applications to the unique business requirements by plugging the customized logic into the framework. With a high degree of extensibility, the framework itself can become more applicable to different types of business applications. However, in creating a framework, its extensibility should always be determined in the context and assumptions of the application you are trying to develop. Each time you increase the extensibility of the framework, your developers may need to write more code and require more detailed knowledge about how the framework operates, which will have a negative impact on their productivity. An extreme scenario of a highly extensible framework is Microsoft's .NET framework itself, which is designed for development of a wide variety of applications. Indeed, there are few constraints in developing applications using the .NET framework, but as a result, you lose the benefits of what an application framework can provide. The key is to add the flexibility and extensibility to the places in the framework that are more likely to change in the particular type of application you are developing.
Simplicity
The term "simplicity" here means more than just being simple. Simplicity refers to the way the framework simplifies development by encapsulating much of the control of process flow and hiding it from the developers. Such encapsulation also represents one of the distinctions between a framework and a class library. A class library consists of a number of ready-to-use components that developers can use to build an application. However, developers must understand the relationships between various components and write process flow code to wire many components together in the application. On the other hand, a framework encapsulates the control of such process flow by prewiring many of its components so that developers do not have to write code to control how the various components interact with each other.
Maintainability
Maintainability, the ability to effectively support changes to the application as a result of changes to the business requirements, is a welcome side effect of code reuse. Framework components are commonly shared by multiple applications and multiple areas within a single application. Having a single copy of the framework code base makes the application easy to maintain, because you need to make a change only once when a requirement changes. The application framework may also contain many layers. Each layer makes certain assumptions about the business the application is intended to serve. The bottom layer consists of framework components that make no assumptions about the business. They are also the most generic components in the framework. As you move higher up the stack of the layers, its components depend on more business assumptions than do the previous layers, and hence are more susceptible to change when business requirements and rules change. When changes do occur, only the components at the layer where the business assumption is broken need to be fixed and tested. Therefore, by injecting different levels of business knowledge into different levels of the framework layers, you can reduce the cascade effect of changing business rules and requirements to the application. This also leads to the reduction of maintenance costs, since you need to touch only the code that is affected by the business rule change
To better understand how we can develop an application framework, we need first to understand what goes in an application framework and its relationship to other parts of the system.
Framework Layers
Framework Development Techniques
In order to develop an effective application framework, you need to know some common techniques for framework development. The following list shows some useful techniques and approaches that can help you develop a framework that is both easy to use and extensible.
Common spots
Hot spots
Black-box framework
White-box framework
Gray-box framework
Design patterns
Common spots, hot spots, and design patterns are some of the techniques used in framework development. Black, white, and gray boxes represent the approaches you can take to developing the framework.
.........
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