Identifying Spatial and Temporal Media Fragments on the Web
Lynda Hardman, Jacco van Ossenbruggen · 2007
Semantic descriptions of non-textual media available on the Web can facilitate retrieval and presentation of media assets and documents that contain them. Semantic Web languages can represent controlled vocabularies and shared annotations of media content on the Web. By identifying concepts to consider, Uniform Resource Identifiers (URIs) are the building blocks of the Semantic Web. RDF subject-predicate-object triples provide the mortar by specifying relations between them. Often, particular regions of an image or particular sequences of a video need to be localized (anchor value in [1]) and uniquely identified in order to be used as subject or object resource in an RDF annotation. However, the current Web architecture does not provide a means for uniquely identifying sub-parts of media assets, in the same way that the fragment identifier in the URI can refer to part of an HTML or XML document. Actually, for almost all other media types, the semantics of the fragment identifier has not been defined or is not commonly accepted. The URI specification defines the general meaning for scheme#fragment, and, for example, when the scheme is http, the RFC2616 specifies that a HTTP GET has to be performed to find out what the fragment is, yielding a certain Content-Type in the response (i.e. the mime-type of the fragment). The mimetype registry specifies what the fragment means within a document depending on its type. For example, for ’text/html’ the RFC2854 defines that the fragment is actually a part of the document identified by an anchor. Providing an agreed upon way to localize sub-parts of multimedia objects (e.g. sub-regions of images, temporal sequences of videos or tracking moving objects in space and in time) is fundamental [2, 3, 4, 5, 6]. The requirements for expressing and processing these fragments have been studied [7]. This position paper describes several ways for identifying fragments of multimedia content on the Web using W3C recommendations, ISO standards or RFC.