The Windows Installer Service overview white paper contains:
SummaryThis white paper describes the Windows Installer service--a feature of the Windows® 2000 Professional operating system. The Windows Installer service defines and manages a standard format for application setup and installation, and tracks components such as groups of files, registry entries, and shortcuts. Windows Installer is a system-resident installation service that provides consistent deployment, enabling administrators and users to manage shared resources, customize installation processes, make decisions on application usage, and resolve configuration problems.
Conceptually, the Windows Installer service examines applications as a collection of components (files, registry keys, other resources), keypaths (the path of a given component), and as globally unique component codes. Because Windows Installer manages applications at the component level and oversees resources other than files, it ensures that no resource is installed or removed unless the component that owns it is either installed or removed. In short, Windows Installer monitors what a particular component has installed and cleanly performs uninstall/removal tasks.
To properly maintain the applications and resources installed on the computer, Windows Installer uses an API that administers all file paths for a particular application. With this management API, Windows Installer determines the correct path to specific components and ensures that no applications point to missing files. In addition, the management API assists in on-demand installation and configuration of Windows Installer products and features--including dynamic repairs of applications, upgrades, patching, and keypath verification.