CSC/ECE 517 Fall 2009/wiki3 5 SD: Difference between revisions
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http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGeeYzwI/AAAAAAAAATM/NPsuTSArKIg/s400/DIP1.png | http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGeeYzwI/AAAAAAAAATM/NPsuTSArKIg/s400/DIP1.png | ||
In this diagram, component A depends upon component B, which in turn depends upon component C. Due to these dependencies, each of the higher-level components is coupled with the lower-level components. | |||
The goal of the Dependency Inversion Principle is to decouple higher-level components from their dependency upon lower-level components. This may be achieved by creating interfaces as part of the higher-level component package which define the component’s external needs. This allows the component to be isolated from any particular implementation of the provided interface, thus increasing the component’s portability. The following diagram illustrates this relationship: | The goal of the Dependency Inversion Principle is to decouple higher-level components from their dependency upon lower-level components. This may be achieved by creating interfaces as part of the higher-level component package which define the component’s external needs. This allows the component to be isolated from any particular implementation of the provided interface, thus increasing the component’s portability. The following diagram illustrates this relationship: | ||
http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGil3HQI/AAAAAAAAATU/lezX76UCH7Q/s1600-h/DIP2.png | http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGil3HQI/AAAAAAAAATU/lezX76UCH7Q/s1600-h/DIP2.png | ||
In this diagram, component A provides an interface which defines the services it needs. Component B satisfies this dependency by implementing the interface. The same relationship is additionally shown for components B and C. Take special note that the interfaces are packaged together with the higher-level components and are defined in terms of the higher-level component’s needs, not the lower-level component’s behavior. It is this association of the interface with the client component which logically inverts the conventional dependency flow. | In this diagram, component A provides an interface which defines the services it needs. Component B satisfies this dependency by implementing the interface. The same relationship is additionally shown for components B and C. Take special note that the interfaces are packaged together with the higher-level components and are defined in terms of the higher-level component’s needs, not the lower-level component’s behavior. It is this association of the interface with the client component which logically inverts the conventional dependency flow. | ||
Revision as of 20:13, 14 November 2009
Dependency inversion principle
Introduction
In conventional application architecture, lower-level components are designed to be consumed by higher-level components which enable increasingly complex systems to be built. In this composition, higher-level components depend directly upon lower-level components to achieve some task. This dependency upon lower-level components makes applications rigid, fragile and immobile. Goal of Dependency inversion principle is to decouple the high-level components from low-level components.
What is Dependency inversion principle?
Dependency inversion principle states that:
- High-level modules should not depend on low-level modules. Both should depend on abstractions.
- Abstractions should not depend upon details. Details should depend upon abstractions.
In conventional architecture, higher-level components depend upon lower-level components as depicted in the following diagram:
http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGeeYzwI/AAAAAAAAATM/NPsuTSArKIg/s400/DIP1.png
In this diagram, component A depends upon component B, which in turn depends upon component C. Due to these dependencies, each of the higher-level components is coupled with the lower-level components.
The goal of the Dependency Inversion Principle is to decouple higher-level components from their dependency upon lower-level components. This may be achieved by creating interfaces as part of the higher-level component package which define the component’s external needs. This allows the component to be isolated from any particular implementation of the provided interface, thus increasing the component’s portability. The following diagram illustrates this relationship: http://4.bp.blogspot.com/_rO0OuTtGb2Y/SVgyGil3HQI/AAAAAAAAATU/lezX76UCH7Q/s1600-h/DIP2.png In this diagram, component A provides an interface which defines the services it needs. Component B satisfies this dependency by implementing the interface. The same relationship is additionally shown for components B and C. Take special note that the interfaces are packaged together with the higher-level components and are defined in terms of the higher-level component’s needs, not the lower-level component’s behavior. It is this association of the interface with the client component which logically inverts the conventional dependency flow.
