Acyclic dependencies principle

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The acyclic dependencies principle (ADP) is a software design principle that states that "the dependency graph of packages or components should have no cycles".[1] This implies that the dependencies form a directed acyclic graph.

Example[edit]

Circular dependency example

In this UML package diagram, package A depends on packages B and C. Package B in turn depends on package D, which depends on package C, which in turn depends on package B. The latter three dependencies create a cycle, which must be broken in order to adhere to the acyclic dependencies principle.[2]

Types of dependencies[edit]

Software dependencies can either be explicit or implicit. Examples of explicit dependencies includes:

  • Include statements, such as #include in C/C++, using in C# and import in Java.
  • Dependencies stated in the build system (e.g. dependency tags in Maven configuration).

Examples of implicit dependencies includes:[3]

In general, it's considered good practice to prefer explicit dependencies whenever possible. This is because explicit dependencies are easier to map and analyze than implicit dependencies.

Cycle breaking strategies[edit]

It is in general always possible to break a cyclic dependency chain. The two most common strategies are:[1]

See also[edit]

References[edit]

  1. ^ a b "Granularity: Acyclic dependencies principle (ADP)" (PDF). Object Mentor. Retrieved 2013-06-14. 
  2. ^ Fowler, Martin (2004). UML Distilled. 
  3. ^ "Implicit Dependencies Are also Dependencies". O'Reilly. Retrieved 2013-06-16.