A qualified component is a method of single-level indirection, similar to a pointer. Qualified components are primarily used to group components with parallel functionality into categories. For example, if you have 30 components listed in the Component table that are the same Microsoft Word fax template localized into 30 languages, you can group these together into a category of qualified components by using the PublishComponent table.
Qualified components are entered in the Component table in the same way as ordinary components. Every component must have a unique component ID GUID and component identifier specified in the Component table. In addition, qualified components are associated with a category GUID and a text-string qualifier in the PublishComponent table. Qualified components are referenced by the category GUID and the qualifier, which just points to the ordinary component in the Component table.
For example, a qualified component ID GUID can point to different language versions of a resource DLL. In this case, the group of localized resource DLLs comprises the category and the numeric locale identifiers (LCID) strings are commonly used as the qualifiers. A developer could author an installation package that uses these qualified components to do the following:
- Find the path to a particular language version of the resource DLL using MsiProvideQualifiedComponent or MsiProvideQualifiedComponentEx and install the resource.
- Determine all of the language versions of the resource DLL that are present by calling MsiEnumComponentQualifiers.
- Prepare the application to support additional languages. A future language pack for the application can use the qualified component to add more language versions of the resource DLL.
For more information, see Using Qualified Components.