Data exchange using the IFC standard and BIMserver
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Laura Swaine
DT168 MSc in Construction Informatics
5th
December 2012
Data exchange using the IFC standard and BIMserver
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Abstract
Building Information Modelling (BIM) has developed for use in the Architectural,
Engineering, Construction and Facility Management (AEC-FM) industry for use by multiple
disciplines throughout the lifecycle of buildings. A range of heterogeneous applications and
versions of applications are used across the disciplines to generate building information models
from feasibility stage through to demolition stage. Several standards have been developed to
support data exchange and integration, however, currently there is not a single building product
data model that successfully represents all of the processes involved in a buildings lifecycle;
Open BIM. This report investigates Industry Foundation Classes (IFC) as a means of data
exchange and integration within Revit and the value proposition BIMserver can provide as an
open source building information model server. The case study presented for investigating data
exchange and integration considers benefits, limitations, quality, productivity and software
technology issues.
Keywords: BIM, interoperability, building data product model, open BIM, standards, IFC, data
exchange and integration, model server.
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1. Introduction
A case study is presented utilising a building information model generated in Revit 2013 to
investigate IFC files as a solution to Revit’s inability to save to previous versions of Revit. It is
common within the AEC-FM industry for numerous stakeholders in a project to have access to
and preferences for different model generation and analysis software applications. Interaction
between the different stakeholder’s model view definitions is required for coordination and
review so interoperability is vital; Open BIM. Currently there is not a single building product
data model that successfully transports a digital representation all of the different activities the
different designers follow from feasibility stage through to demolition (Eastman, C.M., 1999;
Sun M. & Howard R., 2002; http://buildingsmart.com/standards/ifc/model-industry-foundation-
classes-ifc, 2012).
Revit’s SQLite database prevents Revit from saving projects to previous versions of Revit.
However, Revit does support IFC files. The case study model is exported from Revit 2013 as an
IFC file and the IFC file is opened in Revit Architecture 2012. Revit does not import Revit’s own
exported IFC files without loss of data; Revit in combination with IFC results in the loss of data.
This case study investigates the extent of the data lost and modifying the IFC mapping file to
prevent the loss of data on exporting the entities.
BIMserver is utilised as an open source building information model server to manage the
case study IFC files. This report explores BIMserver as a way of generating IFC files and the
value it adds to the management and distribution of the IFC files to multiple stakeholders.
2. Case study
2.1 Introduction to the case study model
The building information model utilised in this case study is an architectural model view
definition of an extension to an existing industrial support building. The model was generated in
Revit 2013. The extension totals 293m2, a ground floor of 187m
2 and a mezzanine level of
106m2. Structurally independent of the existing building, the construction of the extension
consists of Kingspan Insulated Panels fixed to a steel frame. The extension is separated from the
Data exchange using the IFC standard and BIMserver
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existing building by a 1hour fire rated Shaftwall partition returned along the adjacent walls for
3m.
Figure 2.1.1 Revit 2013 case study model
2.2 Objective of case study
• Investigate data exchange and integration via IFC, considering benefits, limitations,
quality and software technology issues
• Explore modifying the IFC mapping file to prevent the loss of data on exporting the
entities
• Prove IFC files can provide a solution to Revit’s inability to save to previous versions of
Revit
2.3 Case Study Procedure
1. Export IFC files from the case study Revit 2013 model
3no. IFC file types supported by Revit and based on the IFC 2x3 schema were exported
from Revit 2013; IFC 2x3, IFC Coordination View 2.0 and IFC GSA 2010.
2. Import IFC files
Open the exported IFC file in Revit Architecture 2012 and save as Revit files
3. Review loss of data
4. Modify the IFC mapping file
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2.4 Case study results
1. Export IFC files from model
IFC File Type IFC File Size Revit Architecture 2012
File Size
IFC 2x3 1964 KB 3096 KB
IFC Coordination View 1851 KB 3076 KB
IFC GSA 2010 2022 KB 3104 KB
Table 2.4.1 IFC file sizes
2. Import IFC files
The most commonly used IFC file type, IFC 2x3, encountered the least amount of errors
and warnings.
Figure 2.4.1 IFC 2x3 file, errors and warnings
Figure 2.4.2 IFC coordination view 2.0, errors and warnings
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Figure 2.4.3 IFC GSA 2010, errors and warnings
3. Loss of data
On visual comparison the IFC models appear identical. The level of data lost appears to
be identical in all 3no. IFC files.
Data lost:
• Structural plans and ceiling plans which exist in the default Revit templates (see
figure 2.4.4)
• Site view, section views and schedules created within the Revit model (see figure
2.4.4)
• Topography sub-regions and custom surface patterns assigned to materials within
the Revit model (see figure 2.4.5)
• Gridlines and section markers placed within the Revit model (see figure 2.4.6)
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Figure 2.4.4 Loss of views and schedules
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Revit 2013 Model IFC 2x3 Model
IFC Coordination View 2.0 Model IFC GSA 2010 Model
Figure 2.4.5 Loss of topography sub-regions and surface patterns
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Revit 2013 Model IFC 2x3 Model
IFC Coordination View 2.0 IFC GSA 2010 Model
Figure 2.4.6 Loss of grids and section markers
4. Modify the IFC mapping file
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Figure 2.4.7 Structural columns originally set to IfcColumn in exportlayers-ifc-IAI.txt
file
Figure 2.4.8 Site originally set to IfcSite in exportlayers-ifc-IAI.txt file
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Figure 2.4.9 Ceilings originally set to IfcCovering in exportlayers-ifc-IAI.txt file
Figure 2.4.10 Sections originally set to not export in exportlayers-ifc-IAI.txt file
Figure 2.4.11 Topography originally set to IfcBuildingElementProxy in exportlayers-ifc-
IAI.txt file
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Figure 2.4.12 Wall surface pattern originally set to IfcWall in exportlayers-ifc-IAI.txt file
Figure 2.4.13 Grids originally set to not export in exportlayers-ifc-IAI.txt file
Modifications to the IFC mapping file:
• The structural, site and ceiling categories were originally mapped to the appropriate IFC
classes and yet the structural, site and ceiling plan views are lost on exporting. No
modifications required
• The section category was originally mapped not to export, the IFC mapping file was
modified to IfcBuildingElementProxy
• The topography category was originally mapped to IfcBuildingElementProxy, the IFC
mapping file was modified to IfcSite
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• The wall category including surface pattern was mapped to IfcWall and yet the surface
pattern of the external wall was lost on exporting. No modifications required
• The grids category was originally mapped not to export, the IFC mapping file was
modified to IfcAnnotation
Results of modifications:
On exporting the Revit 2013 case study model as an IFC 2x3 file and opening the IFC
file in Revit Architecture 2012, the section views, topography sub-regions and grids were
lost despite having modified the IFC classes in the IFC mapping file. The loss of data was
identical to the IFC file exported prior to the IFC mapping file modifications.
Figure 2.4.14 IFC 2x3 model (post modifications to IFC mapping file) in Revit
Architecture 2012
2.5 Case study conclusions
Revit 2013 cannot open its own exported IFC files. IFC files exported from Revit 2013 can be
opened in previous versions of Revit; however, data is lost in translation. Productivity and the
quality of the model being exported are affected when data is lost. While all of the geometry is
exported as parametric shapes some of the semantics are lost. In particular semantics associated
with customisations to the standard Revit elements in the default Revit templates are lost. This
suggests that the IFC geometry resource schema facilitates reuse more successfully than the IFC
property resource schema. The International Alliance for Interoperability (IAI) Technical
Committee developed guidelines for developing models, addressing base problems and
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promoting consistency. The guidelines specify that geometry and materials are to be treated as
separate functions:
Recognizing that most objects in buildings have multiple functions, the functions of an
object and its form and material are to be treated separately. An object instance may have
specialised performance properties added to it for uses within an application, but these
properties are not intrinsic (Eastman, C. M., 1999, p.289).
A number of factors preventing the IFC standard from being completed have been documented:
1. The extent of fragmented AEC-FM branch is much more comprehensive than the
extent of fragmented AEC-FM branch is much more comprehensive than the extent
of related industries
2. Unique products
3. Arranged BIM level of detail is not always suitable for all participants
4. Attachment to traditional working methods
5. Growing branch requirements (Pazlar T. & Turk Z., 2008, p363)
Benefits:
• Element categories and sub-categories can be set to not export, the stakeholders in a
project can decide exactly how much of their model view definition to share, as
colleagues on their current project may be competitors for future projects
Limitations:
• Revit cannot import its own exported files without the loss of data
• Elements categories do not have an appropriate IFC class name in all cases, the elements
geometry is exported as a proxy object in the absence of an appropriate IFC class name,
e.g. topography (see figure 2.4.5 and 2.5.1). The sub-regions are lost as a result of the
topography being exported as a proxy object.
Figure 2.5.1
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3. Interoperability
Revit interacts directly with BIMserver via the Revit plugin resulting in an identical level of
data loss as the case study (see section 2.4) as it is essentially exporting the model as an IFC file
and importing the IFC file using Revit’s export and import functions. Until a Revit model can be
exported as an IFC file and the same IFC file can be opened again in Revit without a loss of data
the Revit plugin does not offer BIMserver any additional benefits (http://bimserver.org/2009/05
/25/revit-plugin-to-connect-to-bimserver/, 2012). Building model repositories such as BIMserver
are the future for managing project data but currently some software issues remain (Eastman, C.,
Teicholz, P., Sacks, R., & Liston, K. (2008).
Amor (as cited in Pazlar T. & Turk Z., 2008) wrote about the IFC standard accommodating
the transformation of semantic information between different software applications and each
software application has its own internal semantic representations, therefore perfect semantic
interoperability cannot be achieved. It is possible that we will never achieve perfect semantic
interoperability and we need to achieve an acceptable low level of data loss that will not prevent
smooth collaboration. Other industries have overcome this issue successfully but as Pazlar &
Turk (2008) wrote other industries are not as comprehensive as the AEC-FM industry. In this
industry the range of possible information to be exchanged is vast.
While most other fields whose products are three-dimensional have converted to 3D
modelling and work conventionally using 3D CAD, that transition is just beginning in
architecture. Of all the design fields dealing with 3D products, only the building industry
remains largely 2D and drawing based. The reliance on 2D representations is not because
paper-based representations are better. It is because there are no mechanisms to initiate
changes of such wide impact. In other industries, organisations develop long term
working relations that allow special forms of communication, specifically for exchanging
CAD data. Because the building industry is composed of many small organizations, many
call the construction industry fragmented. This suggests that the organisations best able to
take advantage of CAD may be those vertically integrated, such as design-build
organisations. (Eastman, C. M., 1999, p.29)
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4. BIMserver
BIMserver has many value innovative intelligent functions for the management and
distribution of models that enable higher efficiency and differentiate the users from their
competitors. Managing models and revisions associated with an increasing number of
heterogeneous software applications is becoming increasingly complex and some issues that
arise can be solved by a repository such as BIMserver:
• Supporting exchanges between multiple concurrent applications that both read and write
project data; that is, the workflows are not linear
• Propagating and managing changes that impact multiple application datasets
• When there are multiple authoring applications that must be merged for later use
• Supporting very frequent or realtime coordination between multiple application users
(Eastman C. et al., 2008, p. 88)
IFC 2x3 TCI is currently the only upload option BIMserver provides. Uploaded files are stored
in an object based database for downloading. The system administrator can set a range of other
formats for downloading on an individual project requirement bases.
BIMserver maintains a log of who worked on the model server, what they did and when the
work was carried out. This value innovation affords the stakeholders higher efficiency. Time and
identity stamps are a legal issue (see table 4.1), BIMserver offers a technological benefit
(Somerville J. & Craig N., 2006).
BIMserver utilises a Berkeley database, all of the model entities properties in the database
can be queried. The model browser feature lists a record of all revisions to all of the IFC data.
Improved quality control enables any revision of any model entity to be efficiently located by
any stakeholder. Improved quality control offers the client higher efficiency and differentiation.
BIMserver’s RSS feature, also known as revisions feed automatically updates the main
project virtual revision when a sub-project is revised. Revision feeds are BIMserver’s
notification system for updates and can be checked out. The revision feeds feature saves the
stakeholders time in deciphering if changes have occurred since they last accessed the model
sever. The RSS feature is value innovative and improves the efficiency of the project.
Globally unique ID’s (GUID’s) are utilised by BIMserver’s compare feature. The GUID’s
are compared to produce a list of changes between two IFC file revisions. The differences are
listed by IFC name and GUID and can be downloaded saving the stakeholders time in visually
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comparing two revisions of a model. GUID’s are also utilised by the intelligent merging
function. The compare feature is value innovative, enables the stakeholders to work more
efficiently and offers the client differentiation.
The early warning system monitors workflow collaboration. When a stakeholders checks out
a file as opposed to downloading the model server keeps a log, if a second stakeholder logs into
the model server to upload a new revision they are notified of the active check out. If the
stakeholder proceeds to upload the new revision the first stakeholder is notified the next time
they log into the model server that a new revision was uploaded since their last check out. These
notifications are an innovative quality control measure.
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Benefits of BIMserver Technological
Benefits
Process Benefits Perceived Benefits
Management Issues
Consistency of revisions
Structured data
Reduced handling of documents
Improved administration
Data output
Data import into database
Storage device
Cost savings (note)
Distribution Issues
Speed and transfer of information
Faster response times
Delivery of data
Enhanced processing of
documentation
Distribution costs lower (note) (note)
Legal Issues
Time and identity stamps
Validations of data
Security of process
Safety and reliability
People Issues
Ease of use
Enhanced communication
Interpretation of data
User friendly
Table 4.1 The benefits of BIMserver from technological, process and perceived viewpoint
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Note: A perceived benefit to be measured and calculated for each individual case. Also depends
on current working process (Somerville & Craig, 2006).
5. Current Standards Efforts
A number of standards and efforts have assisted the development of IFC since 1994. The
Technical Research Centre of Finland (VTT), RATAS national building model project, since
1987, and Part 106, the Building Core Construction Model (BCCM), since 1994, in particular
made a significant contribution. The Industry Alliance for Interoperability was started in 1994
and later in 1997 was renamed the International Alliance for Interoperability as Autodesk users
wanted the open neutral IFC standard to be non-proprietary. The IAI drew from the parallel work
of ISO-STEP but in contrast to ISO-STEP the IAI wanted to progress quickly in order to keep
the industry’s interest (Eastman, C.M., 1999). In 2005 the IAI was renamed buildingSMART and
now has regional chapters worldwide. Open BIM is an initiative of buildingSMART and several
software vendors using the IFC standard (http://buildingsmart.com/openbim, 2012).
It has been written that most of the good practices identified in earlier efforts have been
incorporated into the IFC open standard and IFC seems to be a solid response to the need for a
building product data model and the specifications put forward for such a model (Eastman, C.M.,
1999). However, to date IFC requires further development to support a suite of applications
without loss of data. The current IFC version has only partially filled some gaps in the much
needed functionality IFC is lacking. It is yet to be seen if IFC will solve the building industries
data exchange and integration issues.
A step in a positive direction for the industry came in 2011 when the UK Government
announced their intention to require: collaborative 3D BIM (with all project and asset
information, documentation and data being electronic) on its projects by 2016. The BIM Task
Group was put in place bringing together expertise from industry, government, public sector,
institutes and academia. A four year plan was developed to modernise the industry. The groups
aim is to develop more efficient ways for all of the stakeholders in a project to work through all
of the stages in a projects lifecycle collaboratively. Their ambition is to realise this more efficient
way of working through information rich collaborative 3D BIM technologies and processes
(http://www.bim taskgroup.org/, 2012). The AEC-FM industry will be strongly impacted as
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Governments adopt collaborative 3D BIM for use on their projects. The UK Government is not
alone in the attempt to modernise the industry; the General Services Administration and
Singapore have adopted the IFC data model for code checking and design review (Eastman C. et
al., 2008).
Construction Operations Building Information Exchange (COBie) is a working party of the
BIM Task Group and one of the three technical working groups established by Building
SMARTUK. COBie 2.4 is documented for use in the UK (http://www.bimtaskgroup.org/
working-parties/, 2012). COBie is currently being used in the UK as a solution to the
unpredictability and unreliability of IFC. Mapping from COBie to IFC and from IFC is possible
(http://www.bimtaskgroup.org/working-parties/). COBIE is formatted as a subset of IFC, it is a
data schema and can be in the form of a spread sheet or relational database. COBie structures
unstructured data and BIM data as structured single-entry formatted data; this is one of the
advantages COBie has over IFC (http://www.bimtaskgroup.org/building-smart-uk/, 2012). IFC is
considered the long term open source standard solution internationally.
A collection of SQLite databases maintain Revit’s elements, 2013 SQLite databases cannot
transport to previous databases. Revit’s back up files contain databases in tabulated database
format. Revit’s central model is a database, enabling the central model to be opened and adjusted
in Microsoft Access. Local Revit files need to be recreated when a central file is restored from a
backup file as the database has changed. COBIE accesses databases and Revit is a database,
therefore, COBIE is considered more reliable and contractually demanded by the UK
Government.
Tekla Corporation and Solibri Inc. have developed the BIM Collaboration Format (BCF)
schema as another interim solution. This schema is currently pre-release but the intention is for
the schema to inform a software application of issues another software has found in a building
information model. Only the issues will be communicated as opposed to the entire model in the
hopes of improving communication between BIM software applications
(http://www.buildingsmart-tech.org/specifications/bcf-releases/bcf-intro, 2012)
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6. Conclusions and future work
Until the software technology issues within Revit and the IFC data model are resolved and
Revit can be used in combination with IFC without the loss of data, the exchange of data and
data integration will be limited. Depending on the model view definition requirements of the
projects numerous stakeholders, IFC can provide a solution to Revit’s inability to save to
previous versions of Revit. Each stakeholder’s model view definitions geometry is required by
the other stakeholders for review and coordination purposes, IFC can transport geometry. The
general spatial layout of the building is the common thread used in each phase of a buildings
lifecycle (Eastman, C.M. 1999). A BIM integration tool and or automated 3D clash detection
tool may be utilised for coordination purposes but in the event of a previous version of Revit
being utilised by another stakeholder for coordination purposes the data IFC exchanges is
adequate for coordination. The semantics associated with the geometry may not be required by
the other stakeholders in their entirety. The amount of information required by each stakeholder
will need to be accessed on an individual project bases as each application only uses a portion or
subset of the IFC model (Sun M. & Howard R., 2002).
As the construction industry is considered fragmented, the development and automation of
the individual organisations within the industry will benefit the industry as a whole throughout
the lifecycle of buildings. The industry is still largely unprepared for BIM; a portion of the
industry is still designing individually in two dimensions and the portion of the industry working
in teams to design in three dimensions cannot smoothly collaborate. The industry is challenged is
to develop an open source neutral building product data model that can successfully transport a
digital representation of a building project for use by multiple stakeholders in their different
activities throughout a buildings lifecycle. Changes that affect an entire industry inevitably take
time and despite numerous efforts having been made to date there is still not one standard or
model in the AEC-FM industry that can successfully exchange construction data without a loss
of information. The IFC standard may change the current circumstance in the future (Pazlar T. &
Turk Z., 2008). The UK Government believe COBie comes closest to meeting this requirement
at this time. COBie is an area I have highlighted for future study.
BIMserver has many value innovative intelligent functions as a model management and
distribution tool that enables higher efficiency and differentiates the users from their competitors.
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BIMserver adds an extra layer of intelligence to the use of IFC in BIM. Value innovation, higher
efficiency and differentiation have a clear impact on the revenues and profits of a company
(Grilo A., & Jardim-Goncalves R., 2010).
7. References
Eastman, C.M. (1999) Building product models: computer environments supporting design and
construction. United States of America: CRC Press LLC
Eastman, C., Teicholz, P., Sacks, R., & Liston, K. (2008). BIM Handbook. Hoboken, New
Jersey: John Wiley & Sons, Inc.
Grilo A., & Jardim-Goncalves R. (2010) Value proposition on interoperability of BIM and
collaborative working environment. Automation in Construction, 19. 522-530
http://bimserver.org/2009/05/25/revit-plugin-to-connect-to-bimserver/, retrieved November 3
2012
http://www.bimtaskgroup.org/, retrieved December 2 2012
http://www.bimtaskgroup.org/building-smart-uk/, retrieved December 2 2012
http://www.bimtaskgroup.org/working-parties/, retrieved December 2 2012
http://buildingsmart.com/openbim, retrieved December 1 2012
http://buildingsmart.com/standards/ifc/model-industry-foundation-classes-ifc, retrieved
December 1 2012
(http://www.buildingsmart-tech.org/specifications/bcf-releases/bcf-intro, retrieved December 2
2012)
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Pazlar T. & Turk Z. (2008) Interoperability in practice: geometric data exchange using the IFC
standard. ITcon, 13. 362-380
Sommervile J. & Craig, N. (2006) Implementing IT in construction. Oxon, England: Taylor &
Francis
Sun M. & Howard R. (2002). Understanding IT in construction. London, England: Spon Press