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Circular dependencies can cause many unwanted effects in software programs. Most problematic from a software design point of view is the tight coupling of the mutually dependent modules which reduces or makes impossible the separate re-use of a single module.
The acyclic dependencies principle (ADP) is a software design principle defined by Robert C. Martin 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 .
The canonical application of topological sorting is in scheduling a sequence of jobs or tasks based on their dependencies.The jobs are represented by vertices, and there is an edge from x to y if job x must be completed before job y can be started (for example, when washing clothes, the washing machine must finish before we put the clothes in the dryer).
Dependencies arise when an expression in one cell uses a value from another cell. In such a case, the value that is used must be recalculated earlier than the expression that uses it. Topologically ordering the dependency graph, and using this topological order to schedule the cell updates, allows the whole spreadsheet to be updated with only a ...
If a dependency graph does not have any circular dependencies, it forms a directed acyclic graph, and an evaluation order may be found by topological sorting. Most topological sorting algorithms are also capable of detecting cycles in their inputs; however, it may be desirable to perform cycle detection separately from topological sorting in ...
A mechanism relying purely on reference counts will never consider cyclic chains of objects for deletion, since their reference count is guaranteed to stay nonzero (cf. picture). Methods for dealing with this issue exist but can also increase the overhead and complexity of reference counting — on the other hand, these methods need only be ...
In object-oriented design, the dependency inversion principle is a specific methodology for loosely coupled software modules.When following this principle, the conventional dependency relationships established from high-level, policy-setting modules to low-level, dependency modules are reversed, thus rendering high-level modules independent of the low-level module implementation details.
Control dependency is a situation in which a program instruction executes if the previous instruction evaluates in a way that allows its execution. A statement S2 is control dependent on S1 (written S 1 δ c S 2 {\displaystyle S1\ \delta ^{c}\ S2} ) if and only if S2' s execution is conditionally guarded by S1 .