1.1 Definition of scope This International Standard defines a language and underlying model for the representation of "hyperdocuments" that link and synchronize static and dynamic (time-based) information contained in multiple conventional and multimedia documents and information objects. The language is known as the "Hypermedia/Time-based Structuring Language", or "HyTime". HyTime can represent time in both the abstract, or "musical" sense, and in user-defined real-time units. It also provides a way of relating the two so that elements of time-dependent documents can be synchronized. NOTE 7 This facility extends to the representation of multimedia information the power, once limited to conventional documents, to distinguish intrinsic information content from style considerations. HyTime's techniques for representing its time model are equally applicable to spatial and other domains; all are treated as systems for measuring along different axes of a coordinate space. Arbitrary cross-references and access paths based on external interactions ("hypermedia links") are also supported. HyTime's time representation contains sufficient information to derive the durations of both control ("gestural") data (e.g., control information for audio or video hardware) and visual data (e.g., a music score, presentation storyboard, or television script). The media formats and data notations of objects in a HyTime hyperdocument can include formatted and unformatted documents, audio and video segments, still images, and object-oriented graphics, among others. Users can specify the positions and sizes of occurrences of objects in space and time, using a variety of measurement units and granularities. Temporal requirements of applications ranging from animation to project management can be supported by choosing appropriate measurement granules. NOTE 8 This International Standard does not address the representation of audio or video content data, but simply defines the means by which the start-time and duration of such data can be synchronized with other digitized information. Nor does it specify the layout process by which occurrences of unformatted documents and other information objects can be made to fit the positions and sizes specified for them. HyTime is an enabling standard, not an encompassing one. As a result, the objects comprising a HyTime hyperdocument are free to conform to any application architectures, or to document architectures imposed by standards, and to be represented in any notation permitted by those architectures. Only the "hub document", which may determine the hyperdocument membership, must conform to HyTime in addition to any other architectures to which it may conform. HyTime is designed for flexibility and extensibility. Optional subsets can be implemented, alone or in conjunction with user-defined extensions. The Hypermedia/Time-based Structuring Language (HyTime) is an SGML application conforming to International Standard ISO 8879 — Standard Generalized Markup Language. The hyperdocument interchange format recommended in this International Standard is ISO 9069, the SGML Document Interchange Format (SDIF). SDIF is defined in Abstract Syntax Notation 1 (ISO/IEC 8824) and can be encoded according to the basic encoding rules of ISO/IEC 8825 for interchange using protocols conforming to the Open Systems Interconnection (OSI) model. Other interchange formats can also be used. 1.2 Field of application The field of application of HyTime is "integrated open hypermedia" (IOH), the "bibliographic model" of hyperlinking wherein an author can, by a suitable reference, link to anything, anywhere, at any time. Because of HyTime's modular design and flexible conformance rules, implementations need support only those facilities that are within their present capabilities. User investment in hyperdocument preparation is nevertheless encouraged because of the well-defined upward-compatible path to a full hypermedia solution. HyTime is intended for use as the infrastructure of platform-independent information interchange for hypermedia and synchronized and non-synchronized multimedia applications. Application developers will use HyTime constructs to design their information structures and objects, and the HyTime language to represent them for interchange. NOTE 9 The HyTime language is not intended for encoding the internal representation of information on which application programs act while executing. Applications can use HyTime to represent hyperdocuments containing information that is at any stage of rendition, from"revisable" to "optimized for interactive access". An application can also choose to convert a rendition of a HyTime hyperdocument into an optimized form for transmission or interactive presentation. NOTE 10 Whether the HyTime representation of a hyperdocument can be used in a local file system for direct access by programs will depend on the type of information in the hyperdocument, the speed of the platform, and the functions performed by the applications that access the hyperdocument.