Design Process

In previous section, the current ontology development methodologies were discussed and after a detailed analysis, Methontology [46] was found to be the most appropriate and applicable development methodology that can be related to the development process of our Device Ontology. In this section we discuss the activities and tasks that were involved in the process of building the Device Ontology, in relation to each of the devel- opment stages in Methontology.

Specification

This is the initial stage in the development of an ontology, where the reasons for building the ontology and its intended uses are identified. As discussed in the previous sections the motivation and the main reason for the development of the Device Ontology was to facilitate semantic discovery of devices and their services. It is also intended to provide a general description framework, to facilitate any application that needs to understand about device capabilities and resources; such as in agent communication scenarios dis- cussed in [49] or content adaptation discussed in [24]. However it is important to note that our Device Ontology describes devices from a ‘usage’ point of view, where the characteristics of the device that are relevant to a user seeking to utilise the device are described. It does not describe the device from a ‘product design’ point of view, as in the case of the ontological framework provided in [76] where the internal dynamics of a device are modelled.

Conceptualisation

This refers to the stage where the domain to be modelled is analysed using the available knowledge sources8, and a semi-formal specification is constructed based on tabular and graphical representations that can be understood by the personnel involved in the ontol- ogy development. This involves: identification of the relevant terms (and their meanings) in the domain to be modelled, and thereby identifying the concepts in the ontology and building the concept taxonomies; identification of properties and relations among con- cepts; analysis of any knowledge in the domain that needs to be modelled as axioms and defining the formal axioms. Knowledge sources in the case of the Device Ontology development were: technical specifications of devices (as in product catalogues); device and service description methods in existing service discovery protocols such as service templates in Service Location Protocol (SLP) [118] and service records in Bluetooth

8_{Sources which are used to gain an understanding about the concepts and relations that should be}

[15] and other approaches for device description such as the FIPA device ontology[49], CC/PP[24] and UAProf [132]. Technical specifications of a variety of devices were stud- ied, which helped to identify the attributes and properties of devices which characterises their capabilities and functionality. The existing approaches for representing device ca- pabilities, such as SLP service templates and FIPA device ontology were also helpful in determining the important properties and characteristics that should be represented in a device description. By using these sources, a conceptual structure was built con- sisting of the concepts to be modelled in the ontology, their taxonomic relations, their attributes and properties and axiomatic knowledge. Additional technical sources were referred, to obtain additional domain knowledge and to clarify certain technical details (for example to clarify the relation between the concepts of transmissive, reflective and

trans-reflective, and to be certain that back-lit referred to exactly the same concept as transmissive).

An important step in the conceptualisation stage was to determine, which concepts, properties and relations in the domain are general enough to be included in the top- level Device Ontology. Any concepts and properties that were specific to certain types of devices were left out from the top-level Device Ontology since they could be included in the specific ontology for that device (specific types of devices are described as special- isations of the generic class Device in the Device Ontology, this aspect will be discussed in more detail in section 3.4). For example Communication Method (such as Ether- net and Infrared) and Storage Media (such as optical disk and flash memory) can be considered as general concepts that will be required to describe the characteristics of a range of devices from computers, cameras, printers and mobile phones and hence will be included in the Device Ontology. Whereas the concept Printing Technology (such as Inkjet, Laser and Dot-Matrix) will be useful only in describing the characteristics of a printer, and hence this will be left out from the top-level Device Ontology (to be included in the Printer Ontology).

Implementation

This stage involves formalising the conceptual model built in the previous stage and representing this in a formal ontology language. The ontology was implemented using the Prot´eg´e ontology editor [94], and translated into OWL-DL [140] through the Prot´eg´e OWL plugin. Pellet DL reasoner [104] was used in the background along with Prot´eg´e editor throughout the implementation stage, to check the consistency of the ontology being developed.

Maintenance:

This involves the activities of updating and correcting the ontology as and when neces- sary. Methontology recommends a life cycle based on evolving prototypes for developing ontologies, because it allows for additions and modifications to the conceptual structure in each new version of the ontology [48]. The Device Ontology was in fact developed in

an iterative fashion, by iterating through conceptualisation and implementation stages several times before arriving at the final perceived ontology.