PLaneT has four strategies it uses in order to match a request with an appropriate package that.
Whenever a file requires a package via PLaneT and that requirement is satisfied, the system makes a note of exactly which package satisfied that requirement and from then on always uses that exact same package, even if a newer version is available. This is done to prevent "magic upgrades" in which a program stops working after installation because an unrelated package was installed. Such connections are called links and are stored in a user-specific table called the linkage table.
If the PLaneT client doesn’t have any previous linkage information, it checks its list of already-installed PLaneT packages for one that meets the requirement, and uses it if available. Both PLaneT-installed packages and packages established through a development link (see Development Links) are checked simultaneously at this stage.
If there is no acceptable local package, the PLaneT client sends a request to the PLaneT server for a new package that would satisfy the requirement. The server then finds the newest matching package and sends it back to the client, which then installs it and uses it to satisfy the original requirement.
If the remote server cannot be contacted (or fails in any way to deliver an acceptable package), the PLaneT client consults the uninstalled-packages cache, a cache of all previously-downloaded packages, even those that are not currently installed. PLT Scheme users who frequently upgrade their installations may have many packages downloaded but not installed at any given time; this step is intended to ensure that these users can still run programs even if they temporarily lose network connection.