The Lagered Multimedia Data Model (LdfDhf) aib in the qwcification of multimedia compositions by dividing the problem into smaller, more manageable pieces. In this paper we describe the lower two la~ert of the LMDM, the Data Definition Layer, which allows the qwcification of multimedia objects in a databaae, and the Data Manipulation Layer, which allows the~pecification of temporal~tructurw built from thoue objects. Several ezampleg demondrute the advantage of the layered paradigm: limple~pecificationa, and modular, rvwabie component.
Background and MotivationMultimedia (MM) is not only presentation-driven, it is also data-driven. Although one typically associates multimedia with graphics and sound, MM data may have relevance independent of its prmrttation, such as high volume photo data fkom satellites, much of which is never viewed. Similarly, MM data is eomtimes manipulated without any presentation occurring, as with digital audio mixing. In addition, a eingle data object may have several presentations, such as a video with various CO1OM or resolutions. These issues lead to the conclusion that a MM model must describe both MM data and its presentation, while recognizing the conceptual diference between them.In a reeent paper we introduced a new model for specification of MM data and MM compositions, which follows the layered architecture paradigm [10]. The strength of the Layered Mdtimedia Data Model (LMDM) is its emphasis on sharing, portability, and reueabfity of MM data and abstractions. Figure 1, follows the layered model paradigm. Such an approach, in addition to making a clear separation between data management, presentation management, and user-interaction, has several other advantagea.
The LMDM, shown inFirst, hardwar-and OSspecific concernscan be isolated in particular layers, remdting in a more general model. Second, components defined in one layer can be used in conjunction with diferent sets of components ikom other layers, improving their reusability y. Finally, the layered paradigm has long been accepted in the cornmunie tiona community, and multimedia may be viewed as a novel method of communication.A layered MM model was previously proposed in [7], although the choice of layers was somewhat difFerent. ScriptX, the devic~independent MM scripting language currently under development [6], was also designed around a layered model the general structure of which is sirn.ilar to the LMDM.
Data Definition
LayerThe Data Definition Layer (DDL) allows data specification of a MM data object clae~, and it provides the abstraction of data objects for the higher layers. Objects can include persistent data, instructions to generate data, or a reference to a run-time data generator. Database management tools for accessing and querying persistent data are assumed to be in place. Objects contain metadata describing data format and semantics. Operators are provided for data transfor-
mations. A detailed description of the DDL is pro-
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