Chapter 5. Service Applications and the Managed Metadata Service

Certain functionality is required across web applications in a SharePoint farm, including authentication, search, taxonomy, connectivity to back-end data sources, and user profiles. Users don’t connect directly with these services. Instead, a user-facing web application accesses the functionality it requires from a middle tier of shared services, in which each service provides a specific type of functionality to one or more web applications in the farm or, possibly, to web applications in remote farms.

So, for example, when a user performs a search by using a query web part in a web application, the query web part connects to search services to return results to the user. Searches performed in other web applications can connect to the same search service, to other search services in the farm, to search services in a remote farm, or to federated search services such as Bing.