SGML-UG SIGhyper Document # 1991-1 Rev. 1991/04/01. Source: Charles F. Goldfarb, IBM Almaden Research Laboratory. Note: Dr. Goldfarb serves as Project Editor for ISO/IEC 10744: "HyTime" Hypermedia Time-based Structuring Language. Information About HyTime The Hypermedia/Time-based Structuring Language (HyTime) is an International Standard currently being balloted as a Committee Draft (ISO/IEC CD 10744). The ballot closes July 31. A Draft International Standard will then be published and balloted, with publication of the approved standard expected next year. The following material is excerpted from the standard. DEFINITION A standardized hyperdocument structuring language for representing hypertext linking, time scheduling, and synchronization. HyTime provides basic identification and addressing mechanisms and is independent of object data content notations, link types, processing and presentation functions, and semantics. Links can be established to documents that conform to HyTime and to those that do not, regardless of whether those documents can be modified. The full HyTime function supports "integrated open hypermedia" (IOH) -- the "bibliographic model" of referencing that allows links to anything, anywhere, at any time -- but systems need support only the subset that is within their present capabilities. SCOPE AND FIELD OF APPLICATION 1. Scope This International Standard defines a model and language for the representation of "hyperdocuments" that link and synchronize static and 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, and it provides for relating the two so that all elements of time-dependent documents can be synchronized. NOTE -- This facility extends to multimedia information the ability to distinguish between intrinsic information content and style considerations that is a hallmark of contemporary document representation methods. The time model is extended to visual aspects of multimedia by treating temporal and spatial measurement domains isomorphically, 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. The 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 extents 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 -- This International Standard does not address the representation 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 of 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 extents specified for them. The documents comprising a HyTime hyperdocument can conform to any architectures and be represented in any notation permitted by those architectures. Only the "hub document", which determines the hyperdocument membership, must also conform to HyTime. 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 is an SGML application conforming to International Standard ISO 8879 -- Standard Generalized Markup Language. The hyperdocument interchange format specified by this International Standard is defined in Abstract Syntax Notation 1 (ISO 8824) and can be encoded according to the basic encoding rules of ISO 8825 for interchange using protocols conforming to the Open Systems Interconnection (OSI) model. 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 parts of 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 -- 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 in the rendition cycle, 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 -- 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.