Software framework

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A software framework, in computer programming, is an abstraction in which common code providing generic functionality can be selectively overridden or specialized by user code providing specific functionality. Frameworks are a special case of software libraries in that they are reusable abstractions of code wrapped in a well-defined API, yet they contain some key distinguishing features that separate them from normal libraries.

Software frameworks have these distinguishing features that separate them from libraries or normal user applications:

  1. inversion of control - In a framework, unlike in libraries or normal user applications, the overall program's flow of control is not dictated by the caller, but by the framework.[1]
  2. default behavior - A framework has a default behavior. This default behavior must actually be some useful behavior and not a series of no-ops.
  3. extensibility - A framework can be extended by the user usually by selective overriding or specialized by user code providing specific functionality
  4. non-modifiable framework code - The framework code, in general, is not allowed to be modified. Users can extend the framework, but not modify its code.

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[edit] Rationale

The designers of software frameworks aim to facilitate software development by allowing designers and programmers to devote their time to meeting software requirements rather than dealing with the more standard low-level details of providing a working system, thereby reducing overall development time.[2] For example, a team using a web application framework to develop a banking web site can focus on the operations of account withdrawals rather than the mechanics of request handling and state management.

[edit] Criticism

It can be argued that frameworks add to "code bloat", and that due to competing and complementary frameworks and the complexity of their APIs, the intended reduction in overall development time may not be achieved due to the need to spend additional time learning to use the framework. However, it could be argued that once the framework is learned, future projects might be quicker and easier to complete. The most effective frameworks turn out to be those that evolve from re-factoring the common code of the enterprise, as opposed to using a generic "one-size-fits-all" framework developed by third-parties for general purposes.

[edit] Examples

Software frameworks typically contain considerable housekeeping and utility code in order to help bootstrap user applications, but generally focus on specific problem domains, such as:

[edit] Architecture

According to Pree,[9]software frameworks consist of frozen spots and hot spots. Frozen spots define the overall architecture of a software system, that is to say its basic components and the relationships between them. These remain unchanged (frozen) in any instantiation of the application framework. Hot spots represent those parts where the programmers using the framework add their own code to add the functionality specific to their own project.

Software frameworks define the places in the architecture where application programmers may make adaptations for specific functionality—the hot spots.

In an object-oriented environment, a framework consists of abstract and concrete classes. Instantiation of such a framework consists of composing and subclassing the existing classes.[10]

When developing a concrete software system with a software framework, developers utilize the hot spots according to the specific needs and requirements of the system. Software frameworks rely on the Hollywood Principle: "Don't call us, we'll call you."[11] This means that the user-defined classes (for example, new subclasses), receive messages from the predefined framework classes. Developers usually handle this by implementing superclass abstract methods.

[edit] List of general-purpose frameworks

[edit] See also

[edit] External links

[edit] References

  1. ^ Riehle, Dirk (2000), Framework Design: A Role Modeling Approach, Swiss Federal Institute of Technology, http://www.riehle.org/computer-science/research/dissertation/diss-a4.pdf 
  2. ^ "Framework". DocForge. http://docforge.com/wiki/Framework. Retrieved 15 December 2008. 
  3. ^ Vlissides, J M; Linton, M A (1990), "Unidraw: a framework for building domain-specific graphical editors", ACM Transactions of Information Systems 8 (3): 237–268 
  4. ^ Johnson, R E (1992), "Documenting frameworks using patterns", Proceedings of The Conference on Object Oriented Programming Systems Languages and Applications (ACM Press): 63–76 
  5. ^ Johnson, R E; McConnell, C; Lake, M J (1992), Giegerich, R; Graham, S L, eds., "The RTL system: a framework for code optimization", Proceedings of the International workshop on code generation (Springer-Verlag): 255–274 
  6. ^ Birrer, A; Eggenschwiler, T (1993), Proceedings of the European conference on object-oriented programming, Springer-Verlag, pp. 21–35 
  7. ^ Hill, C; DeLuca, C; Balaji, V; Suarez, M; da Silva, A (2004), "Architecture of the Earth System Modeling Framework (ESMF)", Computing in Science and Engineering: 18–28 
  8. ^ Gachet, A (2003), "Software Frameworks for Developing Decision Support Systems - A New Component in the Classification of DSS Development Tools", Journal of Decision Systems 12 (3): 271–281 
  9. ^ Pree, W (1994), "Meta Patterns-A Means For Capturing the Essentials of Reusable Object-Oriented Design", Proceedings of the 8th European Conference on Object-Oriented Programming (Springer-Verlag): 150–162 
  10. ^ Buschmann, F (1996), Pattern-Oriented Software Architecture Volume 1: A System of Patterns. Chichester, Wiley, ISBN 0471958697 
  11. ^ Larman, C (2001), Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process (2nd ed.), Prentice Hall, ISBN 0130925691 
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