Windows Installer contains significant changes from its predecessor, Setup API.New features include a GUI framework and automatic generation of the uninstallation sequence.A package includes the package logic and other metadata that relates to how the package executes when running.
If there is a mismatch between the current system state and the value specified in the MSI package (e.g., a key file is missing), the related feature is re-installed.
Because a file is the most common type of key path, the term key file is commonly used.
A component can contain at most one key path; if a component has no explicit key path, the component's destination folder is taken to be the key path.
Components are identified globally by GUIDs; thus the same component can be shared among several features of the same package or multiple packages, ideally through the use of Merge Modules.
A key path is a specific file, registry key, or ODBC data source that the package author specifies as critical for a given component.