# An Ontology for Spatio-Temporal Media Management and an Interactive Application
## 3 The Software-Defined Media Ontology
### Design Policies  
To achieve these goals, we established the following design policies:  
1. **Description of spatio-temporal media processing workflow** It is not sufficient to describe only spatio-temporal media to specify the workflow of recording, processing/editing, and playback of spatio-temporal media. It is necessary to describe the equipment and functions involved in each step of the workflow, as well as their setting information and operation details, after clarifying the input-output relationship of spatio-temporal media.
2. **Semantic description with extensibility** Each spatio-temporal media and each workflow stage has its semantic information with some intention or purpose. This semantic information is fundamental and indispensable to express spatio-temporal media, but at the same time, it is not easy to define the scope of expression. Since it is not realistic to comprehensively specify this information in the SDM Ontology alone, it is appropriate to utilize external ontology to describe such information. Meanwhile, if unlimited descriptions by external ontology are allowed, the rigor of the semantic description will be compromised. It is necessary to have a system that allows descriptions utilizing external ontology in a format consistent with the design intent of the SDM Ontology.
3. **Hierarchical object representation** Spatio-temporal media recording is not only performed with a single piece of equipment, but with a combination of equipment. As the recording scale becomes more extensive and more people are involved, the equipment becomes more complex. The types and composition of the recorded media data also become more complex, and at the same time, the semantic information associated with the data also becomes more complex. The same situation occurs in the processing, editing, and playback phases.  
To cope with such a situation, it is appropriate to group devices, functions, and accompanying semantic information related to spatio-temporal media processing as necessary and represents them as hierarchical composite objects. At the same time, the spatio-temporal media itself should be described as a composite object that groups various types of spatio-temporal media and hierarchically expresses them.
4. **Spatio-temporal coordinate representation** Spatio-temporal coordinates are essential information in representing objects that comprise spatio-temporal media. Therefore, spatio-temporal information should be represented as a fundamental component of the SDM Ontology. Considering the diversity of objects to be handled, the spatio-temporal information they contain is also very diverse. Therefore, the SDM Ontology should be able to describe spatio-temporal information flexibly using various coordinate systems. For example, it would be natural to represent the positional information of microphones and cameras in a concert recording in the local coordinate system of the stage. Meanwhile, the location information of a concert venue is generally expressed in terms of latitude and longitude. Similarly, the time axis of video media recorded by a video camera at a concert is generally set to the origin of the recording start time. However, it is necessary to convert the origin of the time axis to correspond to the time in the concert program. Furthermore, when strict time management is required, the error of the built-in clock of the video camera may be a problem. In such cases, a mechanism to express the correspondence between the time axis in the generated video image data and the accurate time axis is required. Therefore, the spatio-temporal information must be a description that can accommodate coordinate transformation and accuracy compensation processing in the processing and editing phases.