# Autonomous Navigation Framework for Intelligent Robots Based on a Semantic Environment Modeling
## 3 TOSM-Based Autonomous Navigation Framework
### Semantic Modeling Framework
#### 3.1.1 TOSM-Based Environment Modeling  
To begin with, we divide the elements that make up the environment into an object, place, and robot. Each environmental element is represented by the explicit, implicit, and symbolic models based on the TOSM, as shown in Figure 2, to include high-level environmental information. The explicit model refers to information that can be obtained directly by processing sensor modalities. It encompasses metric information (pose, velocity, size), geometrical features (shape, boundary), and image information (image features, colors) that can be measured using logical sensors based on sensor models. In contrast, the implicit model consists of induced information based on knowledge models and databases. The relations between environmental elements (e.g., The blue chair is inside of the meeting room.) and facts (e.g., a car is movable.) such as human semantic memory defined in the field of cognitive science [93] can be considered implicit model components. Finally, the symbolic model symbolizes environmental elements so that robots and humans can interact efficiently. Figure 1: The proposed framework consists of semantic modeling framework (SMF) (blue blocks), semantic information processing (SIP) module (orange blocks), and semantic autonomous navigation (SAN) module (green blocks). Figure 2: Triplet ontological semantic model. Each model of TOSM is described based on classes, object properties, and datatype properties, which are terminologies defined in the OWL reference [94]. In the following tables, we explain the environment modeling based on TOSM using the OWL terminologies. We use classes to group resources with similar characteristics for providing an abstraction mechanism. Table 1 lists the example of hierarchical classes for environmental elements. _Object_, _Place_, and _Robot_ are defined as subclasses of the _EnvironmentalElement_, and each class is defined as superclass of the classes expressed in its right column (e.g., _Door_ is a superclass of _AutomaticDoor_). Subclasses inherit the characteristics of superclasses, and the relation between two classes can be defined as \"is-a.\" For example, _AutomaticDoor_ inherits all the characteristics of _Door_, _Object_, and _EnvironmentalElement_; the relationship between _AutomaticDoor_ and _Door_ can be described as \"An _AutomaticDoor_ is a _Door_.\" The classes are used to determine domains and ranges of object properties and datatype properties. Therefore, subclasses can define more specific properties rather than superclasses, such as _AutomaticDoor_ describes _Door_ in more detail. In the case of subclasses for _Robot_, we use the robot description ontology model as defined in [95]. Object properties are used to represent relations between environmental elements corresponding to the implicit model; in the OWL, object properties provide relations between individuals that are members of the classes. The object properties can be defined using object property hierarchy, descriptions, and characteristics. The object property hierarchy in Table 2 expresses the nodes corresponding to the object properties in a tree-like structure; the right child node is a subproperty of the left parent node. We use _SubPropertyOf_, domains, and ranges among the various descriptions of object properties. _SubPropertyOf_ is used to represent the subproperty relations between nodes in the object property hierarchy (e.g., is_FrontOf_SubPropertyOf_ spatialRelation). The object properties can set domains and ranges of each property using the classes. The individual using the property is inferred as an instance of the domain and range class. For example, if \"CIR752 _isLookingAt_ Table34\" and _Robot_ and _Object_ are domain and range of _isLookingAt_ respectively, CIR752 is inferred as _Robot_ and Table34 as _Object_. We use symmetric and transitive characteristics of the object properties. \"The property is symmetric\" means that it is reasonable to exchange the domain and range of the property.