3.2 Modelling domains

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3.4 Research tasks in the ontology development

ontology being built? What type of information should be involved in the ontology? In order to give a clearly visible structure of the objectives, a graphical representation is proposed for each sub-ontology. 3. Definition of the overall framework of the ontology. In this step a list of the main selected concepts (classes) and their formal explanation are presented. 4. Definition of the topological relations and integration with other domain. The core of the ontologies is here presented. Classes and class hierarchies are defined in detail, relationships between classes are established and properties and attributes are identified according to the objectives. 5. Ontology specifications and computation in the ontology editing environment. The presented ontologies have been modelled by using Protégé (Horridge, 2011). In order to design a correct and not redundant ontology, the consistency of the ontology has been checked using an automated tool.

3.2 Modelling domains

When building an ontology for knowledge mapping of a particular domain of interest, it is important to reflect on the different variable the domain depends on. In the presented case, the problem of modelling the construction process for construction workspaces planning and construction activities scheduling is the result of a complex process involving many decision variables, defined as modelling domains5. As a first step for developing

5 (Heijst et al., 1997) distinguish different types of ontologies, e.g. domain ontologies, which express conceptualizations for particular domains; and generic ontologies, whose concepts are considered to be common to many domains.

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Conceptualization of modelling domains which compose the Knowledge Base

Scheduling

Domain

Site workspace

Domain

Time Domain

Building elements

Domain to

KNOWLEDGE BASE

the Knowledge Base, it is necessary to define the different variables at play from which planning and scheduling approaches will be dependent. These domains shall be drawn from the aims of the system applications that will base on such a KB. In our case the aim may be summarized as follow: «the knowledge base should support system and software applications that, based on an Information Model (IFC-based), may work in the branch of construction planning and scheduling». That is why the proposed Knowledge Base does not follow an all-in-one modelling approach but analyze the individual models by considering singularities of each domains separately. This choice of a multi-ontologies system for modelling the construction process is justified on the ground that further interrelations can be specified in order to provide a higher flexibility to the knowledge base so that it is open to other extensions in terms of others domains (e.g., risk analysis, health and safety management, paths planning, monitoring systems, etc.). Overall, the designed Knowledge Base is composed of four modelling domains. They are coded by using the following four sub-ontologies, interrelated as schematized in Figure 3.5. 1. Construction Scheduling Ontology: this ontology contains all those elements for representing the scheduling problem and constraints. It provides a structured foundation for analyzing the information requirements of a construction schedule which should depend on availability and typology of resources, space-temporal constraints, allocation of workspaces and so forth (details in Chapter 4). 2. Construction Space Ontology: it contains the site workspaces representation and the property set able to activate the reasoning mechanisms and the built-in algorithm to allocate workspaces themselves. In fact, workspaces need to be represented with their basic geometrical and capacity properties and need to be linked to the building objects (details in

Chapter 5).

3. Construction Time Ontology: it is the ontology dedicated to the description of temporal properties of site entities in their evolution across time. It also comprises objects to describe possible relations between time periods in order to define the temporal positions among activities, workspaces and building objects. It plays a pivotal role in developing rule-based reasoning mechanisms for minimizing overlapping activities in terms of workspaces. It works by mean of a connection with a Calendar to the Knowledge base (details in Chapter 7). 4. Construction Product Ontology: this ontology represents the domain of Building Information Models (BIMs) and describes the functional, geometrical and topological information of the building objects –products- that the Knowledge Base needs to get.

Based on IFC-schema and more specifically on the ifcOWL ontology, a new sub-ontology has been specified to represent all those ontological objects that a knowledge base, working on the construction planning domain, should include. (details in Chapter 6). The high-level structure of the ontological framework is depicted in Figure 3.6.

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3.6 Graphical representation of the ontological framework of the Knowledge Base capturing the integration of four sub-ontologies and their specification by means of ‘individuals’