Aspect (computer programming)

In computer science, an aspect is a part of a program that cross-cuts its core concerns, therefore violating its separation of concerns. For example, logging code can cross-cut many modules, yet the aspect of logging should be separate from the functional concerns of the module it cross-cuts. Isolating such aspects as logging and persistence from business logic is the aim of the aspect-oriented software development (AOSD), of which the aspect-oriented programming (AOP) paradigm is the most established area.

Aspect-orientation is not limited to programming since it is useful to identify, analyse, trace and modularise concerns (e.g., PREview) through requirements elicitation, specification and design. Aspects can be multi-dimensional by allowing both functional and non-functional behaviour to cross cut any other concerns, instead of just mapping non-functional concerns to functional requirements.

One view of aspect-oriented programming (AOP) is that every major feature of the program, core concern (business logic), or cross-cutting concern (additional features), is an aspect, and by weaving them together (also called composition), you finally produce a whole out of the separate aspects. This approach is known as pure aspect programming, but hybrid approaches are more commonly used, perhaps since there is less of a paradigm shift between object- and aspect-oriented programming. There is a similar situation with early aspect software development (e.g., requirements), with traditional methods being enhanced for aspect-orientation and new models proposed. Non-functional concerns (e.g., security) can crosscut functional concerns (e.g., door must be present). It is possible for functional concerns to crosscut non-functional or functional concerns (e.g., need for more features harms mobility). A uniform approach to representation and composition, similar to the pure approach in AOP, is termed multidimensional representation.

The prism (optics)|prism analogy describes aspects with terms from the domain of light. Like splitting light into its many aspects (different colours) with a prism, you split a problem into its separate aspects. With another prism you can put the different colours back into a white ray of light, and by the process of weaving aspects you can put your solutions for the different aspects of a problem back into a solution for the whole problem.

See also

• Database normalization — minimize needlessly replicated data
• Core concern — the intrinsic and inherent core functionality of a class
• Cross-cutting concern — common functionality orthogonal to core concern
• Inheritance semantics
• Functional normalization
• Orthogonalization — mathematical normalization
• Refactoring — restructuring software