A list of tasks linked by dependency relationships. To run a task, you invoke its dependencies, running those tasks as prerequisites.
Building a software system is a common predicament for software developers. At various points, there are various things that you may want to do: just compile the program, or run tests. If you want to run tests, you need to make sure your compilation is up-to-date first. In order to compile, you need to ensure you've carried out some code generation.
A Dependency Network organizes functionality into a directed acyclic graph (DAG) of tasks and their dependencies on other tasks. In the case above, we would say that the test task is dependent upon the compilation task, and the compilation task is dependent upon the code generation task. When you request a task, we first find any tasks it depends on and ensure they are executed first, if needed. We can navigate through a dependency network to ensure that all the prerequisite tasks necessary for the requested task are executed. We can also make sure that even if a task crops up more than once through different dependency paths, it's still executed only once.
For more details see chapter 49 of the DSL book