Editing Windows Installer (section)

===Key paths===
A ''key path'' is a specific file, registry key, or [[Open Database Connectivity|ODBC]] data source that the package author specifies as critical for a given component. 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. When an MSI-based program is launched, Windows Installer checks the existence of key paths. 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. This process is known as ''self-healing'' or ''self-repair''. No two components should use the same key path.