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Automation in Construction 57 (2015) 239248

Contents lists available at ScienceDirect

Automation in

e lsThese limitations can be overcome by creating stronger links be-tween product catalogues and BIMmodels using semantic technologies.By using the technologies of the Semantic Web, BIM models can be

the conceptual phase, evaluating the performance and costs ofcomponents in the construction phase).be downloaded from catalogues such as Autodesk Seek. However, theinformation dened in these catalogues is still very limited, generallyisolated and rarely associated with other domains (building regulations,energy performance, etc.).

themselves or by third parties. Then, additnecessary for other stakeholders operating witeasy access to that information within their spe(e.g. identifying a set of building components toTypically, during the design process, the design teamneeds to identifythe most adequate components to fulll specic design requirements.The information they need can be accessible in on-line product compo-nent catalogues. For example, a 3D model of a product component can

To overcome these difculties it is necessary, rst of all, to provideproductmanufacturerswithmechanisms that enable them to distributeinformation about their products in the internet, taking advantage ofthe already existing information, facilitated by the manufacturerslinked with external information from other elogues, libraries of design elements, public pro

Corresponding author. Tel.: +34 93 290 24 20.E-mail addresses: gcosta@salleurl.edu (G. Costa), mad

http://dx.doi.org/10.1016/j.autcon.2015.05.0070926-5805/ 2015 Elsevier B.V. All rights reserved.ever, their participationbetween their product

building components is found in different places (e.g. in the server ofthe architectural ofce, in the internet) and formats (e.g. PDF and textles, HTML pages, Excel, databases, Web Services, handbooks).is hindered by the lack of dynamic linkscatalogues and the BIM model.1. Introduction

Building Information Model/Modexpected to facilitate the collaborationin a building project: architects, enginand facilitiesmanagers, and owners. Thto interact with the BIM model duribuilding design and construction procetional phase. Building component maactors in the building modeling proce(BIM) technologies aredifferent actors involvedonsultants, constructionerent actors are supposeddifferent stages of theafterwards in the opera-rers are also important

etc.) on the internet. To facilitate an accurate and efcient selection ofproducts and materials, searches based on different criteria can be per-formed simultaneously ondifferent information sources. These searchescan result in the identication of products which meet the project re-quirements in terms of costs, availability, regulations, applicability,structural conditions, in combination with others. To achieve this, how-ever, two difculties need to be overcome. Firstly, the information aboutproduct components, which is now available online is usually scarceand not very detailed. Secondly, much of the information related toInteroperabilityConnecting building component cataloguesemantic technologies: an application for p

G. Costa , L. MadrazoARC, Engineering and Architecture La Salle, Ramon Llull University, Quatre Camins 2, 08022 Ba

a b s t r a c ta r t i c l e i n f o

Article history:Received 27 November 2014Received in revised form 30 April 2015Accepted 26 May 2015Available online 22 June 2015

Keywords:Product CatalogueBIM ServiceSemantic WebLinked DataOntology

Existing BIM technologies doof manufacturers in the decatalogues and BIM is necessproducts can be obtained frocan be retrieved from a BIMmof SemanticWeb technologiecarried out within the reseaaccesses the information proof structural components du

j ourna l homepage: www.cosystems (product cata-curement requirements,

razo@salleurl.edu (L. Madrazo).with BIM models usingecast concrete components

ona, Spain

provide links to product components that are needed to facilitate the participationand building processes. A deeper integration between product componentfor this purpose. Through the Linked Data approach, information about buildingultiple sources and linked to create semantic descriptions of components thatel via component catalogues. In this article, we present the case of an applicationconnect BIMmodelswith a catalogue of structural precast concrete components,project BAUKOM. As a proof of concept we have implemented a service whichd by the catalogue to assist the design team in the assembly and dimensioningthe project phase.

2015 Elsevier B.V. All rights reserved.

Construction

ev ie r .com/ locate /autcon1.1. Component-based modeling

In the AEC industry, each of the physical elements which makes abuilding (doors, windows, walls, slabs, etc.) can be dened as acomponent. The assembly of these components as abstract

240 G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248representations takes place in the construction of a BIM model. In aBIM model the components are described by means of parametricrules, geometric properties, and other attributes (materials, costs, spa-tial relations,manufacturer, regulations and others) [1]. These attributesrely on the availability of comprehensive, accurate and up-to-dateinformation on the components.

Bevill and Aresnoult [2] contended that there are three key featuresof interest for architects and contractors when they need to select acomponent for a building model: 1. Complete and up-to-date embed-ded information, with all product specications (cost, pricing informa-tion, etc.), 2. Parametric modeling capability, and 3. Complete andopen interoperability. The reuse of data and objectmodels is an impor-tant feature supported by BIM which facilitates the collaborativecreation of building models. Given that the reuse of models not onlythe models of buildings but also those of objects is gaining interestin the building industry, more manufacturers are providing versions oftheir products in BIM formats (e.g. Revit families). However, accordingto the SmartMarket Report series, recently published by McGraw HillConstruction, the availability and use of product models and contentprovided by manufacturers are still limited: Although a growing num-ber of manufacturers produce BIM content for their products, most BIMusers need additional content that supports their specic activities.Typically a combination of internal skills and third party contentcreation consultants are lling this need [3].

Nowadays, manufacturers are providing parametric models of theirproducts using different BIM software to create them without adheringto a common standard. This is because each software has its own ruleson how to model and handle components. For this reason, differentmodels of the same component are currently needed to ensure thatthey can be imported by different programs. At present, the diversityof modeling rules adopted by the different BIM software makes itdifcult to come up with a common procedure to create standardizedparametric objects in. In particular, the interoperability problems thatarise due to the lack of standardized denitions of BIM-based compo-nent models can be mainly attributed to the insufcient capacity ofthe existing BIM software to interpret them unambiguously whenthey are dened using a standard, for example, IFC. This problemalso arises when a BIM model, or a part of it, has to be exchangedamong different BIM software, or distributed between them and otherapplications.

1.2. Role of standards for interoperability

The most commonly usedmechanism to ensure the interoperabilityamong applications is to exchange les using common standards. Thisexchange can be done in two ways: by using proprietary formats,whose scope is limited to the programs of the same suite or, alternative-ly, by using open and neutral standards such as STEP [4], IFC [5] orCityGML [6]. Although the way in which these les are exchanged hasbecome more efcient in recent years with the advent of the cloud,the interoperability problem has yet to be solved [7].

Interoperability plays a key role in the AEC industry by providing alarge variety of tools and applications used by the variety of profes-sionals involved in the design and construction of a building. WithBIM, the different experts involved are expected to exchange informa-tion via the building model. Each expert works on a part of a buildingmodel, but the decisions they take have an impact on the overall project.Even though BIM should assure the congruence of the informationstored in a model jointly built by different experts, often the extractionof a part of the model (to export it to a structural engineering applica-tion, for example) results in experts having to make a new partialmodel from scratch [8]. This is mainly due to two shortcomings: 1. thelack of mechanisms to facilitate the extraction of parts of a model,which contain only the information required for each expert, and 2.the limitations of standards to anticipate the multiple ways to dene a

model to satisfy the needs of the various experts involved. Nowadays,there is no clear solution to overcome these obstacles. The diversity in-herent to AEC projects, the various methodologies used by the multiplestakeholders involved in the building sector, and the commercial strat-egies of the software vendors make it difcult to nd a generic solution[9].

In an attempt to overcome the interoperability problems, theBuildingSMART consortium has developed different technologiesbased on the IFC standard such as BuildingSMART Data Dictionaries(bsDD) [10], Model View Denition (MVD) [11] and Information Deliv-ery Manual (IDM) [12]. The Industry Foundation Classes (IFC) are themost extended ISO open and standardized data schema which startedto be developed in 1994 by the BuildingSMART consortium (formerly,the International Alliance for Interoperability) to support data exchangein the AEC industry. The IFC schema is based on a set of concepts such asclasses, attributes, relationships, property sets, and quantity denitions,to describe information of building models to be exchanged betweendifferent software applications. Using IFC, BIM data can be extractedfrom proprietary software and be exchanged with other applications.BuildingSMART is currently working on the development of newversions of the IFC schema to increase the level of interoperability ofthe BIM model. The IFC4 specication (formerly known as IFC2x4)enhances the previous version with new geometric and parametricfeatures, among others. Each new version of the IFC specication solvessome of the persisting shortcomings from previous ones while somedeprecated parts, which are no longer used, are removed or updated[13].

As a general purpose data model that facilitates the exchangebetween different software applications, the IFC schema cannotanticipate themultiple ways of representing information of the differentBIM software that may exist. Furthermore, its ability to dene the char-acteristics of a model in different ways might hinder its interpretation.Semantically validated IFCmodels can facilitate the exchange of informa-tion tomembers of the project team.However, the lack ofmechanisms torestrict the way in which the constraints are dened in the modelbecomes a problem in keeping this semantic validation [14]. This oftenleads to a lack of practical use of the IFC exchange format aside fromthe most common use cases (e.g. data exchange between architecturaldesign applications and structural analysis programs), unless thislimitation is previously considered by the BIM modelers. In this regard,integrating all the existing modeling rules adopted by BIM vendorsrepresents a big challenge considering the particular underlyingdata structures, the ongoing evolution of CAD/BIM software and thediverse design approaches (e.g. a creative design approach versus anindustrialized one).

Finally, other problemswith the use of standards are related to theiruse. In the case of the IFC standard, the use of large les can hinder theeffectiveness of the exchange format. For example, with large IFC lesdownstream editing sometimes becomes impossible [15]. Sometimesthese les are large because they are generated as faceted geometry,represented by faces and edges, which usually requires storing muchmore information than that contained in a parametric model. However,limitations are more critical at the component level. Most of the currentBIM software tools do not allow users to import/export componentmodels in IFC separately from the building model. Today, only specicsoftware developed by third parties provided as plug-ins that canbe included in theBIMprogram enables importing parametricmodelsof components. An example is the plug-in for importing and exportingIFC les of components in Autodesk Revit 2014 developed by theGeometryGym Company.

The creation of standards for interoperability is a complex issuewhich requires an in-depth knowledge of how the software used bythe industry works as well as how the data is described in them [16].In the AEC industry, the buildingSMART standard, together withCityGML, an open data model for a common representation of 3Durban objects, have become the most widely used and accepted

mechanisms for interoperability. These standards have been successful

241G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248in providing generic vocabularies for exchanging data between AECapplications. However, they do not provide the exibility that is neededin specic conditions, for example, when it comes to meeting the re-quirements of local building codes. This sort of problems could beavoided by converting semantically rich information [17].

As an alternative to the use of standardized formats, other interoper-ability forms can be obtained by creating ad-hoc solutions to resolvespecic problems in scenarios where required. However, standardizedsolutions are needed to overcome the limitations in these formats ina general way through alternative BIM technology methods andapproaches. Several initiatives based on Semantic Web technologieshave been studied over the last years as a valid and an alternativeapproach for interoperability.

1.3. Application case: services connected to the BAUKOM catalogue

In this article, we focus on a particular case of application of theSemantic Web technologies to connect services to BIM models andlinked data of structural precast concrete components, via a buildingcomponent catalogue we created as part of the research projectBAUKOM, co-nanced by the Spanish National Research Plan 20092012. Starting from the basis that information from different datasources related to the building components has been integrated in thecatalogue, we have implemented a service as a proof of concept whichaccesses the catalogue in order to assist the design team (architects,structural engineers) in the assembly and dimensioning of structuralcomponents during the project phase. In this service, features andmodels of products integrated within the catalogue are retrieved usingthe SPARQL query language.

From the data integration perspective, the development of servicesthat link the component catalogue with the BIM model implies: 1. theintegration of different heterogeneous data sources to create thedenitions of the building components in the catalogue, and 2. the link-age of building component models from the catalogue into the BIMmodel. Semantic models (e.g. ontologies) are essential to facilitate ac-cess to different heterogeneous data sources. They act as intermediariesbetween queries formulated by users based on a particular domain(e.g. building components) and the various data sources required toanswer them (e.g. product data bases, building regulations). For thispurpose, an ontology has been created in the BAUKOM catalogue toenable the specication of product data in a parametric format and tocombine it with other integrated data (e.g. taxonomies, buildingstandards and regulations). Semantic information of products describedaccording to this ontology, and accessible through a SPARQL endpoint,can be queried by third parties. Since ontologies can be understood byhumans, different queries can be written based on them using theSPARQL language to develop services to exploit their information.

Once a product is retrieved from the catalogue as a result of invokingthe services we have implemented, a model of the product is integratedin the BIMmodel. However, the BIMmodel is not only the destination ofthe building component models extracted from the catalogue. It is alsothe data source to be consulted in order to nd out which products tthe project under development.

In the following section, we discuss the benets of using SemanticWeb technologies and ontologies to integrate and describe buildingproduct information provided as linked data on the Web and tocreate services that interact with building component catalogues.Sections 3 and 4 describe the work carried out in the BAUKOM researchproject. Finally, conclusions and future work are discussed in Section 5.

2. Creating Building component specications withsemantic technologies

In the last decade, the SemanticWeb has provided newmethods andtechnologies to enable users to nd, share, and combine information in

the internet more easily. The Semantic Web can be briey described asan initiative introduced by [18] in 2001 with the aim of turning the cur-rent web dominated by unstructured and semi-structured documentsinto a web of data. The basic idea behind the Semantic Web is to addsemanticmetadata to the existing data in order to describe data contentand their relations in a formal way so that the meaning of the data canbe processed by machines.

2.1. Introduction to SemanticWeb technologies and Linked Data approaches

A basic tenet of semantic technologies is the separation of meaningfrom data. The purpose of the Semantic Web is to apply these technolo-gies to the Web of data. This way, applications can query data on theWeb for different purposes such as integrating data or drawinginferences from the data available in the Web. To make this possible,the data on the Web should be available in the standard formatsrequired by the tools developed by the Semantic Web, especially thosedata that concern the relationships between the data. The creation ofthese links between data on the Web enables people and machines toexplore them. BernersLee coined this relationship as Linked Data [19].

The application of semantic technologies transforms theWeb into asemantic network that is globally interconnected. Semantic Webtechnologies enable anexplicit representation of themeanings of the in-formation on theWeb bymeans of ontologies. According toGruber [20],an ontology can be described as a formal and explicit specication of ashared conceptualization. These specications are dened bymeans ofclasses, attributes, values, relationships, roles and rules. OWL is themostused language created by theWorld WideWeb Consortium to describeontologies in a formal way.

The Resource Description Framework Schema (RDFS) [21] andWebOntology Language (OWL) [22] are the most frequently used SemanticWeb languages to construct ontologies. They are supported by theWorld Wide Web Consortium (W3C) whose mission is to developprotocols and guidelines to ensure the long-term growth of the web[23]. The specication of ontologies using these languages is donethrough RDF statements. RDF [24] is one of the specications providedby the W3C, a general-purpose language designed to be read andunderstood by computers. Information can be formalized in RDF graphsmade of RDF triples, that is, subjectpredicateobject statements,which represent facts and relations. Therefore, RDF statements can bediagrammed as a directed graph representing facts. In this way, bydening explicit links in these statements as unambiguous referencesthat may refer to data specied in other graphs, it is possible to createa network of linked data available for any application [25].

***The use of SemanticWeb technologies to address interoperabilityproblems in the AEC sector has been proposed by several authors [26,27]. Pauwels et al. [28] has suggested using the semantics and syntaxof RDF graphs to combine models from different CAD/BIM applications.Abdul-Ghafour et al. [29] have proposed an ontology-based approachbased on OWL DL language for capturing, interpreting, and reusing thesemantics of product information, where OWL DL is an OWL sublan-guage based on description logics which provides the maximum ex-pressiveness while maintaining the computational completeness anddecidability. They point out that the denition of mapping rules is oneof the real challenges to address in the future. Going a step further,Bhms et al. [30] have developed a prototype of a Semantic Web-based Open engineering Platform (SWOP) tomodel products. To imple-ment this platform, a reusable ontology for product modeling calledPMO (Product Modeling Ontology) has been created, which acts as abridge between semantic and non-semantic information (documents,drawings, etc.).

2.2. IFC standard and semantic technologies

Although the IFC standard permits the representation of manydomains of the AEC industry, the lack of mechanisms to extend the se-

mantics of the model represents remains one of its major limitations.

specic instances through the Web.

242 G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248Similarly, Pauwels et al. [38] have developed a version of the IFContology in OWL. They have also implemented a converter where anIFC ontology in EXPRESS is partially transformed into the OWL ontology.This converter has been used within an on-line web service developedto provide the conversion of le-based IFC models (uploaded) intole-based IFC/RDF graphs [39]. This way, a service can be accessed byusing a command-line tool (in Java) or by using a RESTfulWeb interface(https://github.com/mmlab/IFC-to-RDF-converter). To transform theEXPRESS version of IFC into an OWL version, ENTITY elements weremapped into equivalent OWL classes and the EXPRESS attributes tothe corresponding equivalent OWL properties. However, the authorsstate that this process could not be fully completed automatically,since some elements of the EXPRESS schema have no direct equivalentin OWL (e.g. WHERE rule constraints, procedural FUNCTION calls).

Other approaches attempt to facilitate the standardization of BIMmodels right from the start, ensuring that all building products instanti-ated in such models contain a minimum of standardized parameters.This is, in fact, themain objective of the BuildingSMARTData Dictionary,a standard created by buildingSMART that relates the terminology ofthe properties of building products in different languages withproperties of the IFC, which are used as references.

2.3. Building product catalogues on the Semantic Web

In recent years, different solutions and prototype implementationsbased on Semantic Web technologies have been proposed to deal withthe problem of modeling information of building products in astandardized way. For example, Patil et al. [40] have proposed anontology-based framework that enables the exchange of meaningsbetween product information resources across different applicationdomains. Product information is described using a language calledProduct Semantics Representation Language (PSRL) and a semi-automatic procedure is used to determine mappings between equiva-lent concepts used in the ontology and the ones used by the applica-tions. In this way, through a product ontology described in PSRL, themeanings associated to a product can be captured. The outcome is aset of minimum requirements necessary to describe product data tobe exchanged among applications rather than a new data model asSTEP does. Themost critical part of the process is themapping betweenontologies. This is achieved by comparing all the term denitions fromboth ontologies using some logical reasoning. However, to representthe semantic equivalence between terms requires dening one-by-In an attempt to overcome them, Beetz et al. [31] have developed anifcOWL specication to translate the EXPRESS language denition ofIFC into anOWL-based notation. The semantic interoperability providedby this specication enables the extension of BIMmodelswith new con-cepts and properties that facilitate its interpretation by applications[32]. This approach is opposed to the current IFC denitions (IfcProxiesand IfcPropertySets) which are circumscribed to the lexical and syntac-tic interoperability levels [33]. Thereby, ifcOWL provides a semanticinteroperability capability, not offered by any other implementation ofthe IFC, for example, ifcXML, an ISO STEP 10303-28 [34] that speciesthe mapping of EXPRESS language denitions to the XML schema andthe associated serialization of instance data les. IfcOWL adds a layerof semantic metadata enabling formalizing data instances in a waythat they may be processed by reasoning engines such as Pellet [35],RACER [36], and others. An advantage of this type of data formalizationlies in its capacity to extract partial models by using graph query lan-guages such as SPARQL [37]. Thereby, it is possible to obtain a graphcontaining only the strictly necessary information for a specic use ortype of application by creating queries on the y. Furthermore, theformalization of the IFC model using Semantic Web technologiesenables to distribute both the denition of the model itself and theirone relationships for each new CAD application in a mapping table.Beetz and de Vries [41] propose an architecture for semantic servicesbased on building product information. As a central part of this architec-ture, the authors have created a lightweight ontology consisting ofconcepts and instances based on the IFC standard applied to buildingcomponents made of concrete. This ontology is part of a four-layerframework implemented as a prototype. In this framework, the ontolo-gy is serialized via RDFa statements that can be indexed by web searchengines. This architecture is presented as an alternative to thebuildingSMART Data Dictionary (bsDD) standard, which is too wideand leaves toomuch scope to interpret the structure and use of conceptsand their instances. The architecture includes interfaces based on SOAPAPIs and SPARQL endpoints to facilitate complex searches in a directway compared to other implementations based on STEP/SOAP, a featurethat enables to address theproblemof heterogeneity of the contents of alarge number of product catalogues from different manufacturers.

Taking a step further to improve semantic interoperability,Chaparala et al. [42] have proposed a methodology based on a neutralcore product ontology that can be combined with the STEP standardto dene product data frommultiple CAD applications in a standardizedway. After exporting a product component model from a CAD applica-tion as a STEP le, the les are loaded in an ontology editor such asProtg by using the OntoSTEP [43] middleware, a plug-in for Protgcreated by the National Institute of Standards and Technology (NIST)that is used to convert EXPRESS schemas to OWL-DL. This approachhas to face the problem of the large amount of the information on theproducts and the lack of mechanisms to manage them.

2.4. Integration of building product data

One of the applications of the Semantic Web technologies is dataintegration. By using semantic technologies, it is possible to collectand combine data from multiple heterogeneous sources usingontologies to provide a homogeneous view of the information to specif-ic users [44]. The use of ontologies for data integration across differentdomains has been investigated by various authors over the recentdecades [45-48]. Different methods and techniques, based on mappingand matching, have been used to deal with the problems of semanticheterogeneity that may arise in the process of data integration.

Semantic Web technologies can be used to create building compo-nent descriptions that combine and link different types of information(for example, product specications, building regulations and costs).In this way, by applying semantic data integration techniques, isolatedand disconnected data from different sources (text les, databases,spreadsheets and web pages) can be linked and formalized using theOWL language specication, and the instance data integrated as RDFstatements. Thereby, relationships between the diverse data can be ex-plicitly and unambiguously established using standardized descriptions.

As the development of services for the BIM process increasinglyadopts aweb-oriented approach, a product catalogue based on differentintegrated information provided as Linked Data accessible on the webseems to be a feasible solution to satisfy the search needs and thereuse of product information for building modeling.

2.5. BIM component providers

One way to achieve greater efciency in the BIM process is to forgelinks between the model and the building products for example:doors, windows, precast concrete components available in the webportals of themanufacturers, product catalogues and commercial librar-ies (e.g. National BIM Library [49], Autodesk Seek [50], Bouw-Connect[51], BIMObject [52], BauBook [53], among others). Most of thesecatalogues provide component models in open (IFC) and proprietary(Revit [54], Allplan [55]) formats that can be used by different BIMapplications. However, open formats are barely chosen because they

usually include less information than those created for each specic

program. Furthermore, not all applications can import models informats such as IFC.

Componentmodels from different manufacturers can be downloadedfrom these catalogues and inserted into a BIM model. However, afterbeing downloaded and inserted in a BIM model the components do notkeep the links with the catalogues. Because of this, an update of theproduct information would not be recognized in the BIM model. Thereare other catalogues (e.g. BIMObject, National BIM Library) that provideadd-on services as plug-ins to enable the connection between the compo-nents of the BIM model and the catalogues, although these connectionsoperate at the software level instead of at the data level, so they mightbe lost if the BIM model which includes the components is accessedfrom other programs.

Semantic Web technologies can be applied to overcome these limi-tations. In the rst place, componentmodels can be referenced througha Uniform Resource Identier (URI), which is used to identify a resourceon the Web. Through this URI, information on a component can beretrieved by accessing the linked dataset described as an RDF graph.The information described in this graph can include links to otherresources related to this component which can be found in the Web.This approach is the one adopted in the development of the BAUKOMcatalogue introduced in the following section.

3. An architecture to create building components catalogues usingsemantic technologies

In the BAUKOM project, carried out from 2005 to 2009 by the re-search group ARC Engineering and Architecture La Salle in collaborationwith PRECAT Hormigones Prefabricados de Catalunya, S.L. a precastconcrete company an on-line catalogue of building components hasbeen developed which is compatible with BIM technology (Fig. 1). Theproducts of the catalogue and services associated to them enable a

design team to retrieve the information that is necessary to modela structural frame made of precast concrete components in a BIMsoftware from the catalogue [56].

An information system architecture has been developed in BAUKOMto interlink: 1. building product catalogues, 2. associated services and 3.BIM software. In this architecture, an ontology has been developed tointegrate information on building components provided by productmanufacturers and other available data sources frommultiple domains.

3.1. Catalogues of building components

In the BAUKOM catalogue, information of products is described bytemplates created by specialists (technical team, consultants) for eachtype of building component (Fig. 2). By means of these templates,manufacturers can describe their products. The data model thatfacilitates the creation of templates and associated products has beenimplemented in a relational database. However, this data model hasalso been implemented as an ontology (BAUKOM ontology) where thedata from the relational database are integrated into a data warehouseto facilitate data interlinking operations with other data sources.

Templates and products can be created through a set of interfaces.Templates stand for representations of the manufacturer productdatasheets where the different relations among the information name, description, creation date, and classications among others aswell as the related data models parametrically described, are explicitlydened. In a template, parameters are used to describe a component.These parameters can be related according to parentchild categories(e.g. a parent concept can be dened by two or more childrenmeasures), or be referenced to other parameters (the value will be setby the referenced parameter). Different units can be selected for eachparameter (length, area, volume, etc.). Each type of unit is linked to amagnitude, for example, the Length unit is linked to the meters

243G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248Fig. 1. Structure of the BAUKOM showing the connection between product catalogues, services and the BIM software.

bje

244 G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248magnitude. Once created by specialists with the aid of themanufacturers,templates can be selected by manufacturers to describe their products.

Products are described using a template selected in the catalogue.Since a product can be described inmultipleways, the attributes includ-ed in a template can be congured in various ways too. For example, aprecast concrete beam component could have wires in the upper orlower parts of the section. Therefore, the template of this componenttakes these two possibilities into account. Once they have been createdusing the templates, products can be searched by end users.

Both templates and products are stored in an SQL database. Eachtime a template or product is published, the data corresponding to thepart of the ontology schema of the catalogue are stored in a triplestore database. This way, the information about components (productsand templates) can be combined with other information, obtainedfrom external data sources that have been integrated using semantictechnologies.

The solution adopted in this catalogue helps to overcome theproblems of data integration of building components mentioned inthe introduction.With this solution, the information about componentsis transformed into a common RDF/OWL representation format. D2RQplatform tools [57] are used to carry out this transformation process.This data integration process has been described in more detail in [58].

3.2. Access to building component data

In the BAUKOM catalogue, product data are generated through dif-ferent modules that are interlinked (Fig. 3). These modules providethe necessary infrastructure to integrate and combine information,

Fig. 2. Interface to dene omaking it accessible to different services through a SPARQL endpoint.In the process of specifying the product data in the catalogue, man-

ufacturers can assign different categories from existing taxonomies(for example, those of MasterFormat, OmniClass, IFC) to the products.They can also assign them product codes. Altogether, the propertiesassigned to the products enable services to identify the type of compo-nent that suits the project requirements as specied in the

Fig. 3. Overview of the data corresponding BIMmodel. Besides, manufacturers can specify the com-patibility of their products with other products, even from other manu-facturers. Knowing which products can be combined with otherproducts is important in order to create a BIM model as an assemblyof subsystems of compatible elements.

Since resources in the Semantic Web are identied by URIs, eachproduct in the catalogue is identied by a URI (e.g. bhttp://www.baukom-catalog.org/baukom/cpo/resource/product/-precat/beam_IN).The last part of the URI corresponds to the internal code used bymanu-facturers to identify the components in their management systems.

3.3. Semantic services to link building components with BIM

Services that implement Semantic Web technologies, or SemanticWeb Services, are usually associated to service-oriented computingwhere data, within a shared domain, are described in terms of concepts,roles and rules [59]. However, in the context of our research, a servicerefers to a piece of software (services on theWeb, desktop applications,or plugins for different BIM software) that uses semantic data on theWeb to solve some specic needs that arise in a design process support-ed by BIM models. In this context, and to further automate BIM actionsby using external linked data information (in this case, provided by theBAUKOM catalogue), several services have been developed usingsemantic technologies.

As a proof of concept, we have developed two services: one to assistin the assembly and dimensioning of structural components (describedin Section 4), and a second one to calculate beamsections. A detailed de-scription of this service has been the subject of another publication [58].

cts for product templates.The information stored in the catalogue can be accessed through aWeb Service and a SPARQL endpoint, enabling services to access thedata to operate with them. The ontology developed in BAUKOM facili-tates the creation of ad-hoc solutions for modeling (e.g. implementedin services), based on the features of a particular template, or on thecombination of several when this is required. For example, structuralprecast concrete components are part of a system based on hierarchical

ow in BAUKOM project.

relationships (e.g. slabs are connected to girders that can be connectedto a column through corbels or brackets, or directly). This way, duringthe assembly of the structure in the BIM model, slab products can beobtained from the catalogue based on the properties of the beamspreviously selected. All products can be congured with values to suitthe design criteria of the manufacturers. Moreover, different templatesto describe the different types of features can be used to describe a prod-uct, features such as the dimensions for structural calculations, materialproperties and embodied energy.

However, there are some limitations in this data model in order tofacilitate the creation of templates and associated products. For exam-ple, it is not possible to specify mathematical formulas in these

of the inferences can be used to search products in the catalogue thatsuit the requirements of a service.

An example of product search in the catalogue is to retrieve all thehollow core slab components that meet the requirements of structuralmodeling. In most cases, these slabs are supported on beams, so theirlengths can be obtained from the boundary of the beams. Knowingthe length of the beam, together with the information about otherparameters that end-users can specify (for example, width and loads),a valid range of height values for hollow core slabs can be calculatedthrough a formula provided by the building safety code on hollowcore slabs [65]. Once a range of heights is obtained, a SPARQL querycan be executed to obtain all the hollow core slab products of thecatalogue with a height within this range (Fig. 4).

The following section describes a service created as a plug-in forAutodesk Revit 2014 to assist in the modeling of structural frameswith precast components. The implementation of the service demon-strates that structural modeling with BIM can be better supported byusing Semantic Web technologies to provide more exible ways todescribe, search and retrieve product information from componentcatalogues.

4. A service to assist precast structural modeling

Along with the catalogue of prefabricated concrete componentsaccessible in BAUKOM, different services can be developed to enhancethe functionalities of BIM software. One of them is a service implement-ed as a plug-in for Revit that facilitates the search of structural precastproducts in the process of their assembly to create building modelingstructures with these components (Fig. 5).

Fig. 4. SPARQL Query to retrieve products with a valid height value.

245G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248templates. This could be necessary, for instance, to include formulas tocheck if a product meets the specication of a particular building regu-lation. Some researchworks have started to dealwith these issues usingSemantic Web Rule languages such as RuleML [60], SWRL [61], N3Logic[62] or JenaRules [63] and rule-based inference engines such as the EYEEngine [64] or Jena Inference Engine [63]. This way, inference processesbased on semantic rules can be applied on BIMmodels and the outputsFig. 5. Service to assist in precThis service enables the automation of searching and integratingcatalogue components corbels and hollow core slabs into a BIMmodel, tasks that often involved a substantial amount of manual work.

In the case of corbel components, the service enables users to searchfor this type of product in the BAUKOM catalogue. After a search, theservice retrieves all the instances that are compatible with the type ofpossible components connected with them (columns and girders).ast structural modeling.

Such relationships between the components are implicitly dened by ataxonomy built-in in the catalogue. Nevertheless, the manufacturer candene explicit relations between certain products. Based on these rela-tionships, the user is provided with a list of compatible products.Besides, this list can be ltered by the user according to different criteria(e.g. type ofmaterial, shape). After selecting a product and downloadingthe corresponding parametric component model in BIM Revit, this canbe automatically positioned in those places in which a column is con-nected to a girder. Through the service interface, the type of positioning

The service works in a similar fashion in the case of hollow coreslabs. Users can search for products of this component in the cataloguebased on different criteria (e.g., number of hollows, dimensions,compression layer). After selecting the type of hollow core slab, it canbe downloaded, placed and congured automatically in the BIM model.In Revit, the placement of structural components such as beams and hol-low core slabs can be handled with the Beam System tool. However, thistool does not facilitate the automatic adjustment of a component to theboundary conditions of the area of themodel where it is inserted. For ex-

Fig. 6. Interface for conguring the automated positioning of corbels.

246 G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248of the corbels can be congured for each oor level (Fig. 6).Fig. 7. Representative situations in which hoample, the Revit tool does not cut a slab component so that ittswithin allow core slabs must t the perimeter..

247G. Costa, L. Madrazo / Automation in Construction 57 (2015) 239248non-orthogonal polygonal area. Neither is this tool able to derive theheight of the slab from the model. Precisely, what the plug-in we havedeveloped does is to get fromaBIMmodel information about the contextin which the component is going to be inserted to set the value of thecomponent parameters (Fig. 7).

This service was developed in collaboration with Precat [66]. It wasproved to be successful for saving production time for modeling theirprojects. It was implemented with Dot NET technologies [67]: WPFthrough Framework 3.5 and 4.0, according to the version of BIM Revit.DotNetRDF library [68] has been used to implement the managementoperations of the ontology and the connections with the productcatalogue.

5. Conclusions

The Semantic Web can be understood as a network that interlinksmultiple domains describing their data by means of exible andstandard languages such as RDF(S) or OWL. In the AEC sector, SemanticWeb technologies can be applied to integrate and connect informationthat is necessary to describe building components stored in cataloguesthat are accessible to BIM applications via dedicated services.

The aim of our research work has been to apply Semantic Webtechnologies to fulll these two objectives: 1. to produce buildingcomponent descriptions using linked data from different sources avail-able on the Web, and 2. to provide services that make the linked dataavailable in the product catalogue accessible to end-users workingwith BIM models. Accordingly, a product component catalogue hasbeen developed and two services have been implemented, one to assistin the assembly and dimensioning of structural components that wepresented in this article, and a second one to calculate beam sections.The implementation of a catalogue and the associated services in themodeling of precast concrete frames with BIM Revit has enabled tovalidate the application of Semantic Web technologies in a real case.

One of the conclusions that can be derived from this research is thatmore efforts are needed to provide parametric descriptions of productsin amore standardizedway to facilitate their integration and processingby BIM software. Semantic Web technologies applied in combinationwith the IFC standard seem to be the most promising path to improvethe interoperability between BIM models and product catalogues. Thisinteroperability is also necessary to facilitate reusing parametric modelsof products provided in catalogues which are interlinked with otherinformation outside BIM.

Future researchwork should contribute to expanding the capabilitiesof the BAUKOM catalogue by integrating new domains related to build-ing energy efciency. This will require an upgrading of the interfaces sothat domain specialists can specify new types of relation between differ-ent domains and the existing ones. Furthermore, the addition of newdomains in the catalogue would enable the creation of new services tosupport the design of energy efcient buildings.

Acknowledgments

The work presented in this article has been carried out with thesupport of the Plan Avanza Competitividad (TSI-020100-2010-327)co-funded by the Spanish National RDI Plan, grant number TSI-020100-2010-327. We would like to thank PRECAT HormigonesPrefabricados de Catalunya for their collaboration in the developmentand implementation of the service to dimension structural componentsthat interact with the BAUKOM catalogue.

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Connecting building component catalogues with BIM models using semantic technologies: an application for precast concrete c...1. Introduction1.1. Component-based modeling1.2. Role of standards for interoperability1.3. Application case: services connected to the BAUKOM catalogue

2. Creating Building component specifications with semantic technologies2.1. Introduction to Semantic Web technologies and Linked Data approaches2.2. IFC standard and semantic technologies2.3. Building product catalogues on the Semantic Web2.4. Integration of building product data2.5. BIM component providers

3. An architecture to create building components catalogues using semantic technologies3.1. Catalogues of building components3.2. Access to building component data3.3. Semantic services to link building components with BIM

4. A service to assist precast structural modeling5. ConclusionsAcknowledgmentsReferences