In computer science, the semantic desktop is a collective term for ideas related to changing a computer's user interface and data handling capabilities so that data are more easily shared between different applications or tasks and so that data that once could not be automatically processed by a computer could be. It also encompasses some ideas about being able to share information automatically between different people. This concept is very much related to the Semantic Web, but is distinct insofar as its main concern is the personal use of information.

The vision of the semantic desktop can be considered as a response to the perceived problems of existing user interfaces.

Without good metadata, computers cannot easily learn many commonly needed attributes about files. For example, suppose one downloads a document by a particular author on a particular subject – though the document will likely clearly indicate its subject, author, source and possibly copyright information there may be no easy way for the computer to obtain this information and process it across applications like file managers, desktop search engines, and other services. This means the computer cannot search, filter or otherwise act upon the information as effectively as it otherwise could. This is very much the problem that the Semantic Web is concerned with.

Researchers in the iMemex project provide the following query examples:

Both of these queries need to parse the file structure, the first one to find a section in a LaTeX document, the second one to find figures and their labels in documents of any format, both of which current OSs don't know how to do.

A user might want te relate in a single query information that is maintained by the file system, such as placement in a folder, and information that is inside a file. With current technology, this query cannot be issued in one single request.

In query example 1 above, the project information is only materialized in the folder hierarchy; the rest of the filters relate to the inside of the file, and some of it needs to parse the file structure (see above). This leads to performing a first query in the file system and further search inside a file.

There is also the problem of relating different files with each other. For example, on operating systems such as Unix, e-mails are stored separately from files. Neither has anything to do with tasks, notes or planned activities that may be stored in a calendar program. Contacts might be stored in another program. However, all these forms of information might simultaneously be relevant and necessary for a particular task.