## 4 Mapping the LBCS into an Ontology  
### Class Hierarchy  
The LBCS standard has three qualities that constrain the ontology mapping process: (1) it is multidimensional, with each dimension structured hierarchically; (2) the level of detail used to classify land use may be flexible, meaning that, for example, it is possible to classify the function dimension of a certain land unit as shopping (higher on the function dimension hierarchy) or as goods-shopping (lower on the hierarchy); (3) each concept in the hierarchy has a numerical code (which is unique within the context of a dimension) and a colour code, in addition to the full name and description. The first quality, the hierarchical nature of LBCS, offers the opportunity to model each concept as an OWL Class and to build the hierarchical taxonomy through the OWL Subclass relation. In contrast, the second and third qualities seem to be better modelled by treating categories as OWL individuals or instances. It was intended to classify parcels and other land units in different abstraction levels, meaning that dimensions, at any abstraction level, should naturally be seen as individuals (or instances). The main reason for this is because there will be object properties that link Land Units to LBCS dimensions and an OWL property always relates two OWL individuals rather than individuals with an OWL class. Regarding the third quality, each category has its own numerical and colour codes. In OWL there are two possible ways of modelling these attributes of LBCS categories, either by using annotation properties in the class or by using data properties, which are asserted in the individual. While the use of properties is compatible with reasoning and allows for the imposition of some structure and restrictions such as range or cardinality, the annotation properties are completely ignored by reasoning and are only there to be read. Deciding to model a concept as class or as an individual is not a straightforward decision but a very controversial issue [27]. We wanted the best of both worlds and therefore chose to allow the LBCS categories to be viewed both as individuals and classes. One way to solve this dual need is through a weak form of meta-modelling known as punning [7]. Punning, in OWL 2.0, consists of declaring a class and an individual with the same name (IRI), so that this entity is viewed either as a class or as an individual, depending on the context. This means that for every LBCS category class there is an individual with the same identifier (IRI). Punning belongs to the OWL2 specification and is correctly interpreted by reasoners following the inference semantics of OWL. This solution fulfils all the requirements stated above, allowing the user to maintain the subclass relation between the categories and assert properties for them (for example: _LeisureActivity hasCode 3000_). In addition, since all categories in all taxonomy levels have a corresponding individual, it is possible to assert properties from any punned category (for example: _SidneyOperaHouse hasActivity LeisureActivity_). The taxonomy was structured using a base class named _LBCSConcept_ that has five subclasses corresponding to the five LBCS dimensions (Activity, Function, Structure, Site, and Ownership). The taxonomy of concepts as defined in LBCS is built by sub-classing each of the dimensions, as shown in Figure 1. As previously stated, every subclass of a dimension will have an individual with the same name for meta-modelling purposes (except the five concepts corresponding to the top dimensions). All sibling classes were declared disjoint and individuals were also declared different from each other. To refine the semantics of the ontology, a covering axiom was added in the LBCSConcept class, and the subclasses corresponding to the five dimensions were declared disjoint, meaning that every member of LBCSConcept must be an individual of either the Activity, Function, Structure, Site or Ownership classes.