Nepomuk File Ontology (NFO) is one of the fundamental parts of NIE. It deals with files and other desktop resources. Files are understood as sequences of bytes stored in a Filesystem or on a Network. It provides subclasses both of a DataObject and an InformationElement. A basic hierarchy of FileDataObject subclasses is provided. It includes a 'normal' FileDataObject, that usually resides on a typical filesystem, but also allows for other kinds of files - those embedded in, or attached to other data items, as well as deleted and stored in a trash folder. This hierarchy is by no means complete. More complete taxonomies, that either add additional FileDataObject subclasses or extend ones provided in this ontology may appear in future.

The cornerstone of the NFO is the nfo:FileDataObject class. It represents files - finite sequences of bytes available from some durable storage medium. This definition explicitly exludes streams (which are potentially infinite) but includes web documents and other resources resolvable via a URL. As mentioned before there are various types of files. They are reflected in the hierarchy of subclasses of the File class. This hierarchy is expected to grow when users add new types of files relevant to their work.

One special case are web documents that are retrieved through a web server and could potentially be created on-the-fly. These are identified via nfo:WebDataObject.

Each file on a hard disk is usually contained within a folder or a directory (the naming depends on the Operating System). They are represented by the nfo:Folder class. The containment relation can be expressed with the nfo:belongsToContainer property. Note that a Folder is an interpretation. It may be applied to a nfo:FileDataObject (representing a folder on a disk), but it can also be applied to an nfo:ArchiveItem (representing a folder inside an archive).

Compressed Files are expressed with an Archive class. It is also an interpretation that may be applied to any piece of data. An important thing to note is that Nepomuk strives for data integration. It shouldn't make much difference if a file is within a normal folder or within an archive. That's why no special case is made for the nfo:fileUrl (deprecated) property for files in compressed archives. In both cases a file should be accessible with a URL. In case of stand-alone files this is simple. Unfortunately there are no standards defining the way to construct URL's for files inside compressed archives. We encourage applications to use conventions established by the Apache Virtual File System project.(FIXME: update to the new way of constructing URIs) For cases when no URL can be constructed for a file (e.g. a picture inside an archive attached to an event in an outlook calendar) the entire containment tree needs to be examined to find ways for accessing a file.

NFO includes basic vocabulary to describe remote resources. To this end basically two classes have been introduced. nfo:RemoteDataObject as a sub-class to nfo:FileDataObject described files on a remote file system which is directly accessible. This includes remote file systems such as ftp, webdav or the like. nfo:WebDataObject describes information resources of which representations (files, streams) can be retrieved through a web server. They may be generated at retrieval time. Examples are pages served by PHP or AJAX or mp3 streams, typically retrieved through the http or https protocol. For relating a remote resource to its URL the nie:url property can just be set to an http:// or ftp:// address.