A building management system for a building system, the building management system comprising: a building system interface configured to receive building system data; a knowledge base configured to receive the building system data, the knowledge base providing a model of the building system, the model including semantic descriptions of the building system data, the semantic descriptions of the building system data being arranged in an ontology; and a user interface configured to access the knowledge base; characterised by: a semantic registration module configured to generate metadata in response to the building system data; a semantic query module configured to make available to user applications functionalities to retrieve and update the semantic descriptions of the building system data; and a semantic service module in communication with the user interface,the semantic registration module and the semantic query module, the semantic service module configured to generate commands to access the knowledge base, to invoke functionalities of the semantic registration module and to interface with the semantic query module; wherein the metadata and building system data are combined to create the semantic descriptions of the building system data; wherein the semantic service module provides mechanisms to populate the knowledge base by gathering the building system data through the building system interface; and wherein the semantic query module receives requests from the semantic service module and generates proper queries and inferences to be executed on top of the knowledge base. a building system interface configured to receive building system data; a knowledge base configured to receive the building system data, the knowledge base providing a model of the building system, the model including semantic descriptions of the building system data, the semantic descriptions of the building system data being arranged in an ontology; and a user interface configured to access the knowledge base; characterised by: a semantic registration module configured to generate metadata in response to the building system data; a semantic query module configured to make available to user applications functionalities to retrieve and update the semantic descriptions of the building system data; and a semantic service module in communication with the user interface,the semantic registration module and the semantic query module, the semantic service module configured to generate commands to access the knowledge base, to invoke functionalities of the semantic registration module and to interface with the semantic query module; wherein the metadata and building system data are combined to create the semantic descriptions of the building system data; wherein the semantic service module provides mechanisms to populate the knowledge base by gathering the building system data through the building system interface; and wherein the semantic query module receives requests from the semantic service module and generates proper queries and inferences to be executed on top of the knowledge base. a semantic registration module configured to generate metadata in response to the building system data; a semantic query module configured to make available to user applications functionalities to retrieve and update the semantic descriptions of the building system data; and a semantic service module in communication with the user interface,the semantic registration module and the semantic query module, the semantic service module configured to generate commands to access the knowledge base, to invoke functionalities of the semantic registration module and to interface with the semantic query module; wherein the metadata and building system data are combined to create the semantic descriptions of the building system data; wherein the semantic service module provides mechanisms to populate the knowledge base by gathering the building system data through the building system interface; and wherein the semantic query module receives requests from the semantic service module and generates proper queries and inferences to be executed on top of the knowledge base.