The vision of the Social Semantic Desktop defines a user’s personal information environment as a source and end-point of the Semantic Web: Knowledge workers comprehensively express their information and data with respect to their own conceptualizations. Semantic Web languages and protocols are used to formalize these conceptualizations and for coordinating local and global information access. The Resource Description Framework RDF serves as a common data representation format. We identified several additional requirements for high-level knowledge representation on the social semantic desktop. With a particular focus on addressing certain limitations of RDF, we engineered a novel representational language akin to RDF and the Web Ontology Language OWL, plus a number of other high-level ontologies. Together, they provide a means to build the semantic bridges necessary for data exchange and application integration on distributed social semantic desktops. Although initially designed to fulfill requirements for the NEPOMUK project, these ontologies are useful for the semantic web community in general.
The ontologies described in this document are developed as an open-source project called Shared-Desktop-Ontologies (SDO). The development process is centered around the SDO Trac repository which is open to contributions from everyone. Additions, changes, fixes, and in general all contributions to the ontologies should go the way of a ticket in that system (a better alternative is very welcome).
The NEPOMUK Calendaring Ontology intends to provide vocabulary for describing calendaring data (events, tasks, journal entries) which is an important part of the body of information usually stored on a desktop. It is an adaptation of the ICALTZD ontology created by the W3C.
The Nepomuk Contact Ontology describes contact information, common in many places on the desktop. It evolved from the VCARD specification (RFC 2426) and has been inspired by the Vcard Ontology by Renato Ianella. The scope of NCO is much broader though.
The Nepomuk User Action Ontology provides basic classes and properties for desktop events.
EXIF is a common standard of basic image metadata used in digital cameras and in image management software. Masahide Kanzaki created an ontology that allows the EXIF metadata to be expressed in RDF. NEXIF is a simple adaptation of the Kanzaki's ontology to fit it into the Nepomuk Information Element Framework.
The PIMO Ontology can be used to express Personal Information Models of individuals. It is based on RDF and NRL, the Nenpomuk Representational Language and other Semantic Web ontologies.
The Nepomuk Information Element Framework provides unified vocabulary for describing native resources available on the desktop. NIE itself contains of classes and properties that comprise the core part of the framework.
The Nepomuk Sharing Ontology defines basic classes and properties for defining permissions with respect to sharing information in a network.
The TMO Ontology can be used to describe personal tasks of individuals, also known as to-do lists. It is based on RDF and NRL, the Nepomuk Representational Language and other Semantic Web ontologies.
The Nepomuk Message Ontology extends the Nepomuk Information Element framework into the domain of messages. Kinds of messages covered by NMO include Emails and instant messages.
NRL was designed for knowledge representation in Nepomuk Social Semantic Desktop applications. While being built on top of the Resource Description Framework (RDF) and the associated RDF Schema (RDFS), it addresses several limitations of current Semantic Web languages, especially with respect to modularization and costumization. These questions seem to be important not only in Semantic Desktop scenarios but also on the general Semantic Web. NRL tackles these questions by including support for two main additional concepts: Named Graphs and Graph Views. Named graphs help coping with the heterogeneity of knowledge models and ontologies, esp. multiple knowledge modules with potentially different interpretations. The view concept allows for the tailoring of ontologies towards different needs in various exploiting applications. This view concept provides also the basic mechanism to impose different semantics on thesame syntactical structure.
The annotation ontology provides vocabulary that enables users to attach custom descriptions, identifiers, tags and ratings to resources on their desktop. Via other properties, the user is also able to make generic relationships between related resources explicit. Some relationships between resources are too general to be included at the domain ontology level. Instead, these properties are also defined in the annotation ontology. Given the high-level status of this ontology, these propreties can be used to link any related resources on the user's desktop, as well as provide custom human-readable textual annotations.
The Nepomuk File Ontology provides vocabulary to express information extracted from various sources. They include files, pieces of software and remote hosts.
The Nepomuk Multimedia Ontology defines metadata properties and classes for multimedia files.
The Nepomuk Download Ontology provides classes and properties to describe file downloads.