Dependency Tracking (Meta Packages) with PEAR
The PEAR installer can be used for tracking project dependencies with a simple package definition file, without having to describe the entire project in that file.
For example, this can be done to ensure that a specified set of PEAR packages are installed on a development environment, into a test environment, and finally into a production environment, all with minimum fuss.
Another reason for using PEAR to track dependencies is to reduce the amount of work required when trying to do this work manually... checking to see if a new release adds required functionality, closes security issues, or includes bug fixes can take time. Add a few more packages and interdependencies to the mix, and the amount of work grows exponentially.
The PEAR installer can take care of all of this for you. You just need to tell it what you want.