The server maintains information about Repository items and which application to launch to open that type of file and where the application resides.
Administrators create file types (technically, new MIME Types) or add file extensions to file types. You may be informed of the new type by your administrator, or you may discover it while browsing or trying to open a file. If there is a file type that your browser cannot open, you are prompted for a program to open it. To avoid that prompt, you need to register the type in your browser or operating system.
The procedure to register new file extensions or MIME types varies with each operating system, its version, your browser, and the browser’s version. Consult the documentation or on-line help of the browser or operating system or ask your system administrator.