Interoperability in the construction sector is a key issue and researchers, developers and designers have tackled since the introduction of CAD systems. Traditionally, engineers, architects and site operators interact and track their information exchange through paper or digitalized drawings and e-mails. With the introduction of Building Information Modelling (BIM) techniques and tools, operators are using new solutions and methods to keep track and exploit these data.
What has been described as traditional method corresponds to Level 0 in well-known BIM levels definition. The concept of BIM level represents the criteria needed for the full collaboration for the industry. In short, if the Level 0 is represented by the above described situation of paper + CAD drawings, with no collaboration, the next levels reach the goal of full collaboration through the implementation of BIM-oriented technologies. The vision for next levels of BIM are described as stages with full collaboration which changes into full integration as top level, Level 3. A fully integrated model allows the integration of services in the same model stored on the internet. The use of Linked Data principles would ease the collaboration and the information exchange in the industry.
BIM4EEB aims at reducing renovation activities timings and costs, considering all the stages of project development. In this context one of the focuses of the project is to develop a framework of ontologies to address the existing efficiency gaps of data sharing and modelling technologies in BIM, testing in real environment the Linked Data technologies.
The Semantic Web principles, introduced at the start of this millennium, represent the theory of a switch of paradigm about how we conceive the Internet. The web as we know it can be considered as a container of information, which have a low level of interaction between them. Humans need to understand and read relations between contents published on the Internet. One page can be cited into another through a hyperlink but still, the interpretation of such data is on the reader. According to its creator Tim Berners-Lee, Semantic Web technologies and methods should transform the web into a unique interconnected database that machine can manipulate, process and understand. Between these technologies there are ontologies, which provide data schemas for this environment.
Ontologies are defined as “a document or file that formally defines the relations among terms” by Berners-Lee. Formally defining objects and their relations permits the comparison of the content of two different databases, for example, and the discovery of common meanings in a way that can be both human and machine readable. Typically, ontologies available on the web are made of a taxonomy and a set of inference rules. A taxonomy comprehends a list of objects, their definitions and their relationship. Axioms instead, make the list of inference rules that express basic rules which allow applications to deduct over data. In order to achieve a better interoperability between operators of the construction sector ontologies have to be developed together with other standard tools and methods, such as identifiers and dictionaries.
The perspective that Linked Data and Semantic Web can achieve in the field of construction have been studied by many researchers, but considering BIM4EEB objectives the motivation can be represented by a simple example. Building elements are often produced off-site and chosen in a second moment as useful part of the building system. The choice of an element (e.g. a door) may be made by a designer, which interacts with a product made by a manufacturer. With the existing IFC data schema, it is difficult to represent all the specification of a building element, from different point of views. As an example, the width of a door in the latest standardized IFC schema is represented by the quantity Width, in QtoDoorBaseQuantities. Also, the designers and the manufacturer may use different languages or use different dictionaries.
This is where the project action can help: a formalized and extended framework of schemas, able to exchange renovation specific data between the actors of the process. In the example information about a building element are exchanged thanks to the properties of ontologies. It shows how, through basic relationship rules, different properties from different ontologies, can be assigned to an object. Every object or property has a unique identifier associated, called Global Unique Identifier (GUI).
In this example it is possible to see the visualize some of the effects of the project: the representation of the object according to the IFC standard can be exploited and at the same time extended for specific use such as renovation processes, sensor data, building energy simulation data, occupant behaviour data, and so on. It represents just a small improvement in the information exchange, but ontologies and Linked Data technologies can enable deduction over data, fast querying and many other features. The effort needed to expand and standardize this method is divided onto two different and parallel levels: the first consists in extending and adapting formats and standards of the IFC schema; the second is related to the development of domain-specific frameworks of ontologies for Building Information Management.
One of the first steps in this direction is the analysis of existing ontologies covering renovation process requirements. Hence, inter-model relationships are investigated, highlighting possible integrations or extensions of existing schemas. As a result, a framework of ontologies, both new and existing, is proposed. At the end of the development, BIM4EEB will test in real renovation scenarios the BIM management system using the linked building data framework here described.