A survey on content-based retrieval for multimedia databases <s> Overview <s> This paper attempts to define an object-oriented database system. It describes the main features and characteristics that a system must have to qualify as an object-oriented database system. ::: ::: We have separated these characteristics into three groups: ::: • ::: Mandatory, the ones the system must satisfy in order to be termed an object-oriented database system. These are complex objects, object identity, encapsulation, types or classes, inheritance, overriding combined with late binding, extensibility, computational completeness, persistence, secondary storage management, concurrency, recovery and an ad hoc query facility. ::: ::: • ::: Optional, the ones that can be added to make the system better, but which are not mandatory. These are multiple inheritance, type checking and inferencing, distribution, design transactions and versions. ::: ::: • ::: Open, the points where the designer can make a number of choices. These are the programming paradigm, the representation system, the type system, and uniformity. ::: ::: ::: ::: ::: We have taken a position, not so much expecting it to be the final word as to erect a provisional landmark to orient further debate. <s> BIB001 </s> A survey on content-based retrieval for multimedia databases <s> Overview <s> An object-oriented data model, MORE, in which the database specification facilities have been extended so that users can specify an object with various structures is presented. The structure of an object is changed by passing messages. MORE also provides a classtype, a user-defined type for classes with similar structures, in order to simplify the specification of class descriptions. The system generates operations useful for the classes by referring to a corresponding classtype. A prototype system and an example application are described. > <s> BIB002
As mentioned in the previous section, the relational data model does not cover all features required for multimedia database retrieval. As a data model that provides a system with better facilities for the management of multimedia data, the object-oriented data model BIB001 , BIB002 has been proposed. The idea of object-orientation is to encapsulate data with a set of operations that are applicable to the data. This framework provides a system with operational transparency. That is, the user does not need to be careful about the heterogeneity of operations caused by different type of data for the purpose of manipulating data but rather the need to send the same message to the different types of data for semantically identical operations. A composite object is considered to be an object that consists of other objects. It enables one to define the part_of relationship among objects which takes an arbitrary structure. In addition to the structural complexity and operational transparency of multimedia data, spatial and/or temporal dimension is inherent in image, video, and audio data. However, the core of the object-oriented data model does not contain a facility for managing spatio-temporal relationships. In the following subsections, we describe studies on the management of spatial and/or temporal relations.