Dependency

In project management, a dependency is a link amongst a project's terminal elements.

There are four kinds of dependencies with respect to ordering terminal elements (in order of decreasing frequency of use):

1. Finish to start (FS)
   • A FS B = B doesn't start before A is finished
   • 
   • (Foundations dug) FS (Concrete poured)
2. Finish to finish (FF)
   • A FF B = B doesn't finish before A is finished
   • 
   • (Entire book written) FF (Last chapter written)
3. Start to finish (SF)
   • A SF B = B doesn't finish before A starts
   • 
   • (New shift started) SF (Previous shift finished)
4. Start to start (SS).
   • A SS B = B doesn't start before A starts
   • 
   • (Project work started) SS (Project management activities started)

There are three kinds of dependencies with respect to the reason for the existence of dependency:

1. Causal (logical)
   • It is impossible to edit a text before it is written
   • It is illogical to pour concrete before you dig the foundations
2. Resource constraints
   • It is logically possible to paint four walls in a room simultaneously but there is only one painter
3. Discretionary
   • I want to paint the living room before painting the dining room, although I could do it the other way round, too

Traditional critical path-derived schedules are based only on causal (logical) dependencies. The critical chain method necessitates taking into account resource constraint-derived dependencies as well.

See also:

• list of project management topics
• project network
• project planning

In computer science, dependency is a state that one object uses a functionality of another object. This may cause changes on implementation of one object can affect that of another object. Supposedly, Information hiding is a way to eliminate dependency to limit influence of changes and improve modularity. Dependencies can be reduced by applying the dependency inversion principle. Examples of dependency relationships are aggregation (is-part-of), inheritance, subtyping, uses and implements relationships.

It also is common in talking about software package management. One software package, in order to work or to be fully functional, may depend on other software packages and thus must be installed also, and their specific versions must be known if backwards compatibility is broken between versions. The Apt package format, as well as some versions of the RPM package format, include dependency information between packages. This is convenient for updating software but can lead to dependency hell.

See also Dependent area

In Behavioral medicine dependence describes a continuum of physical and psychological attachments related to the concept of addiction.