The APM implements a callback mechanism that gives the package programmer a wide-ranging set of options to manage the installation, instantiation, and mounting of her package. Callback procedures must be written in Tcl and are recorded in the packages

package-key.info

• before-install The registered callback is executed before installation, in particular before the package's datamodel is loaded.

• after-install The registered callback is executed after the datamodel is loaded and information about the package recorded in the APM's datamodel.

• before-uninstall The registered callback is executed before the package in uninstalled, in particular before the package's datamodel drop script is executed.

• after-uninstall The registered callback is executed after the package is uninstalled.

• after-instantiate The registered callback is executed after the package is instantiated.

• before-uninstantiate The registered callback is executed before the package is uninstantiated.

• after-mount The registered callback is executed after the package instance is mounted to the site map.

• before-unmount The registered callback is executed before the package instance is umounted from the site map.

Callbacks are optional - a package may provide as many or as few as the programmer finds necessary for proper implementation of the package's semantics.