## 1 Introduction  
Mechanical, electrical, and plumbing (MEP) systems mainly include the heating, ventilation and air conditioning (HVAC), electric, electronic, plumbing, and anti-power subsystems. These systems are groups of components that, when connected, provide specific building services. MEP relationships are necessary to decrease the difficulty and time to locate components during operation and maintenance. In locating the component, the task can be decomposed into two pieces, i.e., topological analyses and logical inferences. The former focuses on the topological relationships of the MEP components, and the latter on their logic chain. If equipment or terminals are topologically connected, they are always spatially linked to each other through the elements, such as pipe fittings or segments. However, the functional relationships among the topologically-connected components are not apparent. On the other hand, the logic chain shows the upstream and downstream connections for each MEP component, which builds up the functional relationships of the MEP system. The functional relationship is useful as the upstream components usually control the downstream ones. For example, the HVAC system consists of several equipment, and the fan certainly controls its downstream counterparts, such as ducts, elbows, etc. The typical logic relationship is shown in Figure 1.  
Setting-up the logic chain to show the upstream and downstream connections among MEP components is important for improving the efficiency of facility management (FM). For example, the logic chain can help locate the upstream valve of a leaking pipe in an emergency. However, on-site FM personnel currently rely on document-based blueprints or their experiences to locate such equipment. Consequently, some of the equipment cannot be located in time because of the complexity in the MEP network and the manpower limitation. Locating the equipment and retrieving its FM-related information are repetitive and time-consuming tasks for both technicians and facility managers. Building information modeling/model (BIM) technology has been heralded as a facilitator to improve the FM efficiency by integrating the FM related information [1]. The application of BIM to FM is beneficial because it provides FM personnel with the opportunity to manipulate and utilize the information associated with the 3D objects and, thus, FM tasks can be conducted in a more scientific, reasonable, and orderly way [2]. These improvements are accrued during the generation and management of facilities' digital specifications and characteristic data [3]. Nevertheless, although the BIM technology enables data integration within the building lifecycle, incongruence between the supply of and demand for has also proved that insufficient valuable information is considered one of the key obstacles of BIM-based FM [4]. A survey demonstrates that more than 80% of the FM time is consumed in finding relevant information that is often disregarded by designers [5]. Enriched as-built BIM delivered to facility managers can save time for information acquisition, thus, it is suggested that the logic tree of the objects should be implemented to facilitate the management of various components within the MEP model [6]. However, manually setting up the logic chain of the MEP components requires tremendous workloads [7]. Hence, a unified logical information rule is necessary to build an accurate MEP logic tree, which benefits not only the operation and maintenance (O and M) management but also the emergency responses associated with the specific MEP component. Substantiated by the facility managers, making use of the MEP model containing the appropriate logic information could save up to 30% work force in locating the equipment and emergency decision-making compared with the traditional MEP database [8]. Existing modeling standards, however, do not include clear definition of the logic chain and, hence, existing modeling tools do not support quick generation of relevant logic information.