Transitive dependency

A transitive dependency is an indirect dependency relationship between software components. This kind of dependency is held by virtue of a transitive relation from a component that the software depends on directly.

In a computer program a direct dependency is functionality from a library, or API, or any software component that is referenced directly by the program itself. A transitive dependency is any dependency induced by a different component, that in turn is directly or indirectly referenced by the program. E. g. a call to a log function may induce a transitive dependency to a library that manages the I/O of writing a message to a log file. Dependencies and transitive dependencies can be resolved at different times, depending on how the computer program is assembled and/or executed: e. g. a compiler can have a link phase where the dependencies are resolved. Sometimes the build system even allows management of the transitive dependencies. Similarly, when a computer uses services, a computer program can depend on a service that should be started before to execute the program. A transitive dependency in such case is any other service that the service we depend directly on depends on, e. g. a web browser depends on a Domain Name Resolution service to convert a web URL in an IP address; the DNS will depend on a networking service to access a remote name server. The Linux boot system is based on a set of configurations that declare the dependencies of the modules to be started: at boot time analyzes all the transitive dependencies to decide the execution order of each module to start.