Object Versioning as a basis for design change management within a BIM context

Transcription

1 icccbe 2010 Nottingham University Press Proceedings of the International Conference on Computing in Civil and Building Engineering W Tizani (Editor) Object Versioning as a basis for design change management within a BIM context M. Nour & K. Beucke Informatik im Bauwesen, Bauhaus-Universität Weimar, Germany Abstract This paper reports on work done at the InPro project within the 6th EU Framework Program for Research and Development. It addresses the problem of change management in early design. It introduces a novel approach where both object versioning as a change management approach and the IFC model as a neutral building information model are integrated together in an open multidisciplinary collaborative environment. Several experimental prototypes for handling the IFC STEP-21 model data, visualization and data management were developed. The paper discusses the basics of IFC Object Versioning and its advantages as well as the encountered problems such as the instability of IFC objects IDs and their impact on the object versioning process. Keywords: IFC, BIM, object versioning, early design, change management 1 Introduction The AEC (Architecture, Engineering and Construction) design process is complex in nature. It includes a lot of iterative work and design quality gates. In the meantime, it involves multidisciplinary design work that can be done sequentially, concurrently (reciprocal communication) or in parallel. The amount of available information in early design phases increases with time in terms of details and quality of the information itself. Thus, the maturity and evolution of the design is directly related to time and the availability of information. Therefore, the design has to pass through several versions or alternative solutions at both the entire design level or at partial designs. In many cases, different design solutions are represented as alternative solutions (variants) or different development stages of the same solution as versions. These versions have to be compared with the original design goals and intentions to test their conformance to the client requirements. In this context, the InPro project has developed several metrics and indicators to measure this performance of the design against constraints. In the meantime, a version can be compared with its predecessor to determine the changing trend in design development, is it improving and moving towards targets or not? Currently, Document Management Systems (DMS) are used to manage design at the document level. Object versioning is a relatively new approach that supports Change Management and Conflict Detection, regardless of the containing document on the object level. This work tries to introduce the results of coupling both the Object Versioning technology with the IFC model to support the multidisciplinary collaborative model based way of working in the early design stages of buildings.

2 2 Object Versioning and IFC 2.1 Object Versioning Object Versioning is an information management system implemented on the object level. Due to the fact that construction design elements are represented in the form of software objects, object versioning makes it possible to have several versions of the content (attributes values) of an object. It basically provides a graph structure of the object s versions and their interrelations. The development of design in terms of addition of new objects, deletion of objects or modifications of attributes values of pre-existing objects can be captured in a graph structure. This structure is capable of representing the development of alternative designs (variants) as a branching in the versioning graph. An example of a simple versioning graph is shown in Figure (1 left and 2 left) and for further information the reader can refer to (Richter and Beucke, 2008). Each design object version represents the state of development at a certain point in time. New versions could be saved by just identifying the differences through comparison with the parent version, i.e. it is enough to save the deltas between object versions in order to be able to navigate through the entire versioning graph and get the full state of each version. Figure 1 Left: IFC Object Versioning Example, Right: The branching of the versioning graph to indicate variants In reality, object versions do not stand alone. They exist within model versions that express the design development state at a certain point in time. Thus object versions are interconnected through model versions as Directed Graphs that are entangled with each other through (edges) arcs of both graphs to represent changes in the model. Meanwhile, the same object version can be a member of several model versions. Mathematically, the Object Versioning System can be expressed using the Algebra of Sets as a System of Sets that consists of model versions and their relationships as well as object versions and their relationships. Calculating the object status (attributes and corresponding values) is done according to the relationships between model versions, i.e. edges that join the various nodes on the model versioning graph as shown in Figure (1 left) and Figure (2 left). On the contrary to Document Management Systems, object versioning deals with a much finer degree of granularity, that is the object and its attributes rather than documents. This is considered to be one of the most tangible advantages of object versioning that enables and gives more flexibility to

3 the process of creating data subsets or partial models on one hand and on the other hand enables the integration of data subsets to compose new Models, i.e. Configuration Management in design. 2.2 IFC Exchanging IFC (Industry Foundation Classes) partial model data has proved to be a difficult process due to the fact that most software applications have to map the IFC data sets to their own data structures. Irrelevant IFC data is not capable of being re-exported from those applications. Consequently, it is quite difficult to guarantee a lossless data exchange between applications. However, the creation of data subsets specific to certain software applications, model view definitions or user requirements is seen as a probable solution to the IFC STEP-21 (ISO P21, 2002) data exchange problems. In this connection, Object Versioning has a strong potential to solving the above mentioned round trip IFC data exchange problem between applications. However, this necessitates the existence of a new layer in the data exchange workflow. This layer is represented in the Workbench, Sandbox or Private Workspace concept described later in this paper. 2.3 IFC Object Versioning If the IFC as a BIM concept is applied within an object versioning environment, this would with no doubt help overcome many of the problems and barriers that are hindering adopting the BIM way of Figure 2 Left: A simple IFC Object Versioning Graph Right: A complex IFC versioning graph. working. It has been proved within the context of the InPro project (InPro-D6, 2008; InPro-D18, 2009; and InPro D15b, 2009) that early design management activities can benefit a lot from the application of the model based way of working through an object versioning system that would allow dealing with objects rather than documents. The above figure gives an overview of combining IFC and object versioning through the versioning graph visualization. It can be noticed from Figure (2-left) that a new object version is only created whenever there is a change in the object s attributes values. If not, then the same object version is shared among several model versions. It can be seen that IfcSite, IfcBuilding and IfcBuildingStorey are shared between the two model versions (1 and 2). Meanwhile, each model version has a different version of the same IfcWallStandardCase. In the same figure (right), a graph of a much more complex model is presented. It can be seen that the shared IFC objects lie in the middle and are shared by two model versions. In the meantime, the objects that are changed and consequently new versions are created lie at the left hand side of the graph. It is also worth mentioning that the

4 edges of the graph joining the nodes representing the old and new objects contain the (delta values of the changed attribute values). This is used to calculate the status of the object at any point in time with regards to its position on the graph without having to duplicate any data. 3 Developed IFC tools A set of experimental tools (prototypes) were developed by the author to provide a proof of concept for the IFC object versioning system. The following is a brief summary of the developed tools. 3.1 IFC Toolbox In order to be able to carry out any experimental work on the IFC model, there was a need to develop an open access platform that enables dealing with the IFC model and its underlying technologies away from any proprietary software development. The developed platform is capable of generating new early binding libraries for any available IFC EXPRESS schema. The toolbox is capable of importing any IFC STEP file and converting it to Java /.NET runtime objects. It is also capable of doing modifications on the imported models and finally exporting them either as whole or partial IFC models. (Nour and Beucke, 2008). 3.2 Visualization In general, humans can derive overview of information from data better and faster if it is represented in a suitable visual format other than textual/numerical scripts or tables. This is why human beings are especially attentive to certain symbols (Duncan, 1989). This phenomenon is also explained as the ability of large amounts of visual / diagrammatic information to be processed by the human visual perception system in parallel as opposed to the serial processing required for textual or numeric information (Ware, 2004; and Larkin, 1987). Figure 3. Graphical Support for Object Versioning using geometrical appearance and IFC spatial tree In the scope of this work, data representation in the produced prototype is visualized graphically and fully coupled with interactive tools like zooming and filtering, details on demand windows and predefined parametric query fields which allow users to browse through and study the represented IFC data. Furthermore, emphasis is also placed on the rapid filtering of data to reduce the result sets as well as showing both geometrical as well as alphanumeric differences between different versions of the same object. Most of the geometrical differences can be directly identified by the user. However, there are some cases where the differences are too small to be identified with the naked eye. Therefore, different visualization properties are assigned to the objects to trigger the user s attention to the

5 change. Three types of visualization were found to be particularly important for an IFC object versioning environment; 1) the 2D/3D CAD view, 2) The IFC spatial tree structure and 3) The model and object versioning tree graph with zooming and filtering functionalities to avoid crowded unreadable diagrams. These types of views are supported by interactive user functionalities that enable the user to fully navigate through the IFC model as a whole, as a partial model by queries (according to attributes) / selection or by filtering according to object types, or by selecting chronological / alternative design versions as shown in Figure 2 and Figure Partial Model Exchange Partial Model exchange and the production of data sets relevant to (MVDs) Model view Definitions are not only concerned with the exchange of objects geometry as some CAD applications do, but rather concerned with geometry as well as other alphanumeric attributes and relations between object. Thus, there was a need to manage partial model exchange not only on the basis of the geometrical representations of objects. Hence, (FIOPE) a Flexible Instance Oriented Partial Exchange Environment has been developed within the toolbox (Nour, 2007). The developed approach mainly depends on involving end users in the development / deployment process of the IFC partial model exchange. It enables end users who are not IFC experts to merge models coming from different sources in addition to splitting partial models and defining their content. 3.4 Private Workbench Concept The main idea of the private workbench is based on having a central IFC data hub, with which all project s stakeholders can communicate. Since it is difficult to force all BIM authoring tools to adhere to certain exchange protocols regarding the preservation of GUIDs in addition to the IfcOwnerHistory attributes, the private workbench was introduced as an optional intermediate layer between the central model server and the stakeholder s client software, where all communications take place over the Internet in the form of IFC STEP ISO files. It is mainly used to facilitate collaborative concurrent design work among team members from one side and to regulate and control the exchange of shared data with the central model server from another side. Furthermore, the private workbench provides a private zone where each partner is allowed to have intermediate versions and only commits work to the central model server at certain development stages of the design. Moreover, private data and corporate know how can still be kept within the boundaries of the stakeholder s organization (Nour, 2008). 3.5 Updates and GUIDs The major advantage of object versioning is the ability to handle BIM updates. In perfect conditions, where the BIM authoring tools keep the GUIDs of the IFC objects and relations, the changes in the object s attributes can be recognized as a result of a comparison process. In the scope of this paper, the entire IFC model is mapped to an object oriented database that is capable of creating the versioning relations on both the model and object levels. At model updates, only changes to objects attributes are saved as deltas on the edges of the versioning tree. Thus, when visualizing the model, all new objects that were not members of the precedent model as well as modified objects are assigned a user defined colour (Java3D appearance). Therefore, the user is able at a glance to get hold of the newly added or modified elements that are highlighted graphically as shown in Figure (3). Practical experience through the developed prototypes shows that it is very difficult to depend merely on the IFC GUIDs as a basis for versioning the objects. GUIDs are very useful if they are correctly managed, however, if this is not the case, then they create more problems than they solve. Hence, other techniques for object recognition in terms of geometry, topology and semantics have to be added to the private workbench (workspace) layer in future.

6 4 Conclusions The role of object versioning in model based information management systems has been emphasized and validated through the output deliverables of the InPro project (D-18 InPro, 2009; D15b-InPro, 2009). Object Versioning has succeeded to respond to the early design process demands and characteristics. It proves to be a very efficient tool in: 1) Handling the increase of design data and details (quantity and quality) through time. 2) It ensures the consistency and validity of shared design data despite of the iterative design pattern of work. 3) It supports shifting from the paper based 2D information handling to 3D BIM related interactive models. 4) It supports dealing with design data in terms of change detection, conflict detection, variations management, workflow approval and tracing changes. 5) It supports concurrent design through the developed private workbench concept, where early design activities are not linked to a fixed sequential workflow pattern. It has been proved that if IFC is applied through an object versioning environment, this would help overcome many of the problems and obstacles hindering the adaption of the model based way of working. Dealing with the IFC model on the object level gives a higher degree of flexibility to the process of creating data subsets or partial models, in addition to the integration of data subsets (partial models) coming form different sources, i.e. Configuration Management in design. Depending on GUIDs only proves to be problematic in many cases where, BIM authoring tools do not respect the IFC entities GUIDs in round trip model exchange. Therefore, other aiding tools and algorithms are being developed to help tracing the IFC objects finger prints throughout several versions of the IFC model. Acknowledgements This research relates to InPro, an integrated project within the 6th EU Framework Program for Research and Development ( References DUNCAN, J. and HUMPHREYS, G.W., Visual search and stimulus similarity. In: Psychology Review 96(3) (1989) INPRO D6, Open Standards for Interoperability between Applications in Early Design. Ed: Thomas Liebich and Mathias Weise. Deliverable of the NMP-EU project InPro (IP ). INPRO D18, Overview of Information Management Applications based on Object Versioning. Ed: Mohamed Nour. Deliverable of the NMP-EU project InPro (IP ). INPRO D15b, Overview of Early Design Appliations. Ed: Juha-Matti Houttu. Deliverable of the NMP-EU project InPro (IP ). ISO STEP, Industrial automation systems and integration Product data representation and exchange part 21: Implementation methods: Clear text encoding for exchange structure, LARKIN. J. H. and SIMON H. A., Why a diagram is (sometimes) worth ten thousand words? In Journal of Cognitive Science 11 (1) (1987) NOUR, M. M., Manipulating IFC sub-models in Collaborative Teamwork Environments. In: Proceedings of the 24th CIB W-78 Conference. Maribor, Slovenia, June ISBN NOUR, M. M. and BEUCKE, K., An Open Platform for Processing IFC Model Versions. Tsinghua Journal of Science and Technology, 13, NoS1, ELSEVIER, RICHTER, T. and BEUCKE, K., A concept for Utilizing Versioned Object Models in Engineering Applications. In: proceedings of the Twelfth International Conference on Computing in Civil and Building Engineering, Tsinghua University Beijing, China. WARE, C., Information Visualization: Perception for Design, Morgan Kaufmann, USA.