4.3 Topological structure

Workspaces. To schedule an Activity, it is necessary to choose Resources that produce the time intervals to assign to each activity depending on their capacity level. 11. Milestone, (Mi) = {mi1,...., min}. A Milestone represents a Phase finalization and is connected to a given Time Instant.

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4.2 Textual notations used in the body of the text in order to distinguish the ontology objects

4.3 Topological structure

After having identified classes, in this paragraph is depicted the framework model of the scheduling ontology in terms of the classes, properties and relation diagrams. For readability sake and to enhance the understanding of the discussion, different font and text colors have been used to highlight ontological objects and to distinguish their belonging to the different ontologies that compose the Knowledge Base (Figure 4.2). Core class of the present ontology is ConstructionMethod, being other classes dependent on it. In fact, by using the relationships and properties listed below each construction method is described in terms of required resources, activities and workspaces. All these classes are inextricably linked in an intelligent framework. Since a ConstrucitonMethod produces or consumes a number of construction products, the class ConstructionProduct contains a list of individuals which represent the building elements (e.g. columns, beams, slabs, walls, etc) and their information requirements, and provide the main interface for connecting the scheduling problem to a given Information model IFC-based. For this reason, it follows the structure of the IFC schema and mainly includes sub-types of IfcBuildingElement. Moreover, in order to carry out a certain Construction Method within a given construction site, some Condition is implied to exist before (precondition) or after (postcondition). Also, a Construction Method isDescribedBy a WorkDescription which specifies with generic terms its execution, the allocation of spaces and the required resources. A WorkDescription, in turn, can be defined as a Procedure or a SafetyRule depending on a set of principles or conditions specified in the class Demand. This means, for example, that if the user links two workspaces to a construction method the system automatically classifies this relation depending on the workspace: a procedure if it’s a safety space, a safety

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4.3 Class hierarchy in the construction scheduling ontology: resources types on the left side and constraints types on the right side

rule if it’s hazard space. Each procedure or safety rule contained in a Demand requires a number of Resource. The class Resource is also central to the definition of our scheduling ontology. It represents an entity which is assigned to a Construction Method for its execution. Each Resource can handle one or more activities simultaneously and is provided by a specific property set. These properties are all those which effect its availability and utilization in function of its specific Capacity (e.g., hasCapacityLevel). Making efficient use of Resources in supporting activities becomes then the key-task managed by the rule-engine in solving the scheduling problem. A resources class hierarchy has been proposed which models each sub-class in terms of its dynamically changing amount of CapacityLevel. The class hierarchy is explained in Figure 4.3 and the main class restrictions are depicted in Figure 4.4. Going on, an Activity isFollowedBy an interrelated set of sub-activities. To define a schedule, each Activity is related to the MicroLevelWorkspaces required to be performed in site. A Process is modelled as an abstract entity which isComposedOf a number of Activities. More Processes make up a Phase which ends with a Milestone and requires MacroLevelWorkspaces

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4.4 OWL restrictions to specify the scheduling ontology as regards to the resources’ types

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4.5 OWL classes restrictions as regard the scheduling ontology

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4.6 Visualization of the ontological graph representing classes and relations of the Construction Scheduling Ontology (Snippet from the Ontology Modeling Environment Protégé)