# An Ontology for Spatio-Temporal Media Management and an Interactive Application
## 3 The Software-Defined Media Ontology
### Description of Class Definitions  
#### 3.3.1 **Context**  
Class  
The **Context** class is a class for comprehensively describing the various metadata of the SDM Ontology primary class. Figure 3 shows the structure of the **Context** class and its subclasses. In the figure, the white arrows indicate a **Context** class in which the source node is a subclass and the destination node is a superclass. The vocabulary associated with the arrows between the classes is an object property. The **hasContext** and **isContextOf** properties can be used to associate the **Recorder**, **Processor**, **Player**, **Media**, and **Context** objects with **Context** objects. When associating the **Recorder** and **Player** objects with the **Target** and **Content** objects, the **records**, **recordedBy**, **plays**, and **playedBy** properties express the intention more clearly. Figure 3: **Context** class structure and related classes. Figure 2: SDM Ontology core structure. As described in Section 3.1, it is difficult to define the scope of metadata representation. The SDM Ontology specifies only the following four classes as subclasses of the **Context** class, which are considered necessary to express the relationships among the classes defined in the SDM Ontology. 1. **SDMEvent** subclass: This subclass represents and expresses the entire recording act. Typically, it includes the whole recording of an event, such as a concert or sporting event. By describing **SDMEvent** in a nested structure, events can be divided and expressed hierarchically according to the content creator's intent. It is also possible to integrate and express multiple events. 2. **Target** subclass: This subclass represents the recording target. The recording target represents not only physical objects such as performers, instruments, instrument parts, and orchestras in a concert recording but also abstract objects such as the recording intention of microphones and cameras installed in various places in a concert hall. 3. **Program** subclass: This subclass represents the title of a song in a concert or the program of an event. These are the main attributes of the recording target. 4. **Content** subclass: This subclass describes the editorial intent and revision description of spatio-temporal media. Just as the **SDMEvent** subclass represents the act of recording, the **Content** subclass represents the act of editing. Typically, this subclass manages the editing history and completed content. Semantic descriptions that consist of descriptions other than the above definitions are not specified in the SDM Ontology because they are considered to be information of a nature that should be expressed using the vocabulary of an external ontology. Instead, objects of the **Context** class are assumed to be used as relay nodes to link the objects defined in the external ontology. In this sense, a **Context** object is a standard interface object for linking objects represented in the SDM Ontology and objects defined in external ontologies. As a result, it is possible to describe the semantic information of the primary class objects in a unified manner. Let us consider the Music Ontology [18; 19] as an example of an external ontology that describes semantic information. The Music Ontology can describe various semantic information related to music, such as artist names, song titles, compositions, and performances. On the other hand, the **Context** class of the SDM Ontology only specifies the minimum semantic information necessary to define the SDM Ontology. However, by describing links from **Context** class objects to the semantic information described in the Music Ontology, it should be possible to assign semantic information that incorporates the results of the Music Ontology. In the same manner, it is possible to link to various external objects described in other ontologies via **Context** class objects. It can hence be said that the SDM Ontology has flexible extensibility in semantic information description.