**2.1.4 Conceptual modelling of telecommunications service domain ontology**

After the acquisition of a large number of telecom service related concepts, we need to make the concept classification, concept aggregation, and remove the duplicated concepts according to certain domain knowledge and logic. The goal of this step is to construct a conceptual model of TSDO. This concept model describes the involved domain concepts and their relations of each sub-ontology in detail. Note that, the relationships between the concepts not only involve the concepts of the same sub-ontology, may also be related to the concepts of different sub-ontologies. The concrete building of conceptual model is divided into three steps: (1) **Defining classes and class hierarchy**. In the process of defining the classes, we need to discover the inheritance hierarchy between the concepts and then distinguish the super-classes and sub-classes. (2) **Defining the properties of classes**. After the class is defined, its properties should be considered. There are two kinds of properties. One is datatype property, which is used to describe the features of the concept itself, such as name, age. The other is object property, which is used to depict the relationship between the concepts, like friendship relation between two people. (3) **The definition of domain axiom and knowledge**. When we use ontology to describe the real word things, there are often some contradictions or errors occurrences resulted by human negligence. For example, the range value of one person age property is negative, or a person has two biological fathers. To prevent these common-sense errors, some domain axiom and knowledge should be established. The axiom is to restrict the relationships of the concepts to ensure the consistency of domain knowledge, such as the range value or cardinality of properties.

Fig. 5. Part conceptual model of network ontology.

scenarios. In this step, modellers need to list the collected concepts, relations and explanations as far as possible. It's unnecessary to care about the meaning overlap between the concepts and to consider how to express these concepts and their relation in class, property or instance ways. For example, Figure 4 briefly shows the concepts collection about

After the acquisition of a large number of telecom service related concepts, we need to make the concept classification, concept aggregation, and remove the duplicated concepts according to certain domain knowledge and logic. The goal of this step is to construct a conceptual model of TSDO. This concept model describes the involved domain concepts and their relations of each sub-ontology in detail. Note that, the relationships between the concepts not only involve the concepts of the same sub-ontology, may also be related to the concepts of different sub-ontologies. The concrete building of conceptual model is divided into three steps: (1) **Defining classes and class hierarchy**. In the process of defining the classes, we need to discover the inheritance hierarchy between the concepts and then distinguish the super-classes and sub-classes. (2) **Defining the properties of classes**. After the class is defined, its properties should be considered. There are two kinds of properties. One is datatype property, which is used to describe the features of the concept itself, such as name, age. The other is object property, which is used to depict the relationship between the concepts, like friendship relation between two people. (3) **The definition of domain axiom and knowledge**. When we use ontology to describe the real word things, there are often some contradictions or errors occurrences resulted by human negligence. For example, the range value of one person age property is negative, or a person has two biological fathers. To prevent these common-sense errors, some domain axiom and knowledge should be established. The axiom is to restrict the relationships of the concepts to ensure the consistency of domain knowledge, such as the range value or cardinality of properties.

**2.1.4 Conceptual modelling of telecommunications service domain ontology** 

Fig. 5. Part conceptual model of network ontology.

network ontology.

Figure 5 shows the conceptual model of network ontology in part. Based on the terminologies collected in the above step, the class hierarchy and relationships are described. This conceptual model depicts the classification of network, the services provided by network and the operator of network. It can be seen that the ranges of object property "operatedBy" and "provides" are the concepts from ServiceRole and ServiceCategory subontologies respectively. In addition, we define the domain axioms through the constraints way. For example, we define that "FixedNetwork" is disjointed with "MobileNetwork", i.e. if N1 is an instance of concept "FixedNetwork", then it will not be an instance of concept "MobileNetwork".

#### **2.1.5 Formalization of conceptual model of telecommunications service domain ontology**

As the conceptual model is one high-level abstract model and independent of any concrete ontology modelling languages, we need to formalize this conceptual model through a specific ontology modelling language like OWL (Web Ontology Language) (W3C, 2004a). In general, we can use the common ontology modelling tools to formally describe the terminologies, relationships and axioms in the conceptual model. Figure 6 shows the formalization description of part concepts and relationships of Figure 5 by OWL language. The concept is formally defined by "owl:Class", and the class hierarchy is organized by "owl:subClassOf". The "owl:ObjectProperty" is used to describe the relationships between the concepts and the "owl:disjointWith" clearly depicts the restrictions on the two disjointed concepts.

Fig. 6. Part of network ontology formalized by OWL.
