This research paper addresses the challenges in exchanging project management information within the construction industry, particularly focusing on construction schedules. The current reliance on XML or spreadsheet-based ifles for schedule exchange leads to information loss and misinterpretation in commonly used project management software. Diverse scheduling practices across construction companies, software preferences and organizational structures contribute to a lack of standardization. Existing data schemata for schedule description lack detailed representation of the hierarchical structure of construction processes and their dependencies, limiting automated interpretation. To fill this gap, this paper introduces a minimal ontology designed for representing construction schedules' processes. A case study demonstrates the ontology's application in automated schedule interpretation, emphasizing its potential for automated linking between schedules and corresponding BIM models, reducing manual eforts, and enhancing overall eficiency. It concludes by discussing its broader implications in the Architecture, Engineering, Construction, and Operation (AECO) industry.
Navigating the complexities of exchanging project management information of construction projects
presents several challenges that impede seamless collaboration and hinder the full potential of
automation. Presently, schedule exchange is mainly based on XML or spreadsheet-based files. These files result
from export functionalities of project management software tools. However, this translation process
from proprietary data formats to open formats often leads to loss and misinterpretation of the exchanged
information [
While there are existing data schemata designed for schedule description, such as Industry
Foundation Classes (IFC), Digital Construction Ontologies (DiCon), Digital Twin Construction Ontology
(DTC), Construction Tasks Ontology (CTO), and Internet of Construction Ontology (IOC), they exhibit
limitations that hinder their efectiveness [
To fill this gap, the present paper will introduce a minimal ontology for representing processes of construction schedules. A case study is presented that uses the new process representation for automated schedule interpretation and the linking with a corresponding IFC model to demonstrate the ontology’s suitability and usefulness. This is only one of many possible applications for the ontology. Another advantage of using the ontology is that it facilitates coordination between contractors and subcontractors through structured schedule exchange. Due to the enhanced semantic information, the schedule can be interpreted automatically, reducing the need for extensive manual eforts, streamlining digital processes and improving the overall eficiency. Also, the semantic information about the processes can be used to check the schedule for consistency and completeness.
This research is structured as follows. Section 2 provides background information and elaborates on the identified research gap by introducing existing process-related schemata. Subsequently, in Section 3, the developed process ontology covering process dependencies and decomposition criteria is introduced. One possible application of the ontology is demonstrated in the case study in Section 4. The paper closes with a discussion and conclusion in Sections 5 and 6.
Planning complex construction projects involves addressing challenges such as long project duration, a
multitude of stakeholders, and the unique nature of each project [
The WBS often reflects the organizational structure of the construction company. It should always
be ensured that every work package can be assigned to a single responsible person. An essential
principle here is to avoid consolidating tasks executed by multiple parties into a single work package,
fostering unambiguous responsibility allocation. In this way, the WBS is influenced by the part of the
subcontracted work and the company’s hierarchical structure. Additionally, the WBS forms the basis
for other breakdown structures, including resource, cost, and product breakdown structures, providing
a comprehensive foundation for project management [
The WBS is an essential starting point for creating the construction schedule [
To gain a comprehensive understanding of potential decomposition criteria, existing classification
systems within the construction field ofer an extensive overview of construction-related concepts. They
divide construction concepts into diferent categories to create a common structure and comparability
across projects. There are many nationally and internationally applied classification systems which are
similar but yet diferent from each other. Some national classifications are, e.g., MasterFormat, Uniformat,
OmniClass, and CoClass, while ISO 12006-2 and ISO 81346-12 are international examples [
Several existing data schemata allow for representing construction processes. Some of them are introduced and discussed here to present their suitability for schedule exchange and automated schedule interpretation.
The Industry Foundation Classes (IFC), maintained by buildingSMART International [
Construction processes can be represented with the class IfcTask. To form hierarchical structures
of processes which are relevant for describing a complete construction schedule, IfcTasks can be
nested infinitely. Moreover, process dependencies can be described through IfcRelSequence, which
defines several types of sequence types like start-to-start and end-to-start. An example of using these
entities in combination is shown in Figure 2. Finally, the internal sequence of a task can be described
by using IfcProcedure and IfcEvent [
Several aspects hinder the use of IFC as a means to schedule exchange and automated interpretation.
The Model View Definition (MVD) concept is supposed to reduce the number of entities to be supported
by the implementing software vendor according to a well-defined use case. However, MVDs do not
yet exist for pure process models or combined BIM-process models (4D models). This creates a large
overhead for an implementer who aims only at the process-related entities [
The Digital Construction Ontologies (DiCon) are a set of interrelated ontologies developed by Zheng
et al. [
The Construction Tasks Ontology (CTO) has similar limitations. CTO is a minimal ontology that
describes various construction tasks, including installation, modification, removal, inspection, and
reparation. These tasks are linked to their target entity through the relationship cto:isSubjectOf Task.
While the ontology was mainly designed for the maintenance of historical buildings, it is still applicable
to other construction-related scenarios. Like DiCon, however, CTO can only define task successors with
the relationship cto:afterFinishedTask, which does not consider diferent types of process sequences [
The Digital Twin Construction Ontology (DTC) is an ontology developed in the frame of the
EU Horizon 2020 project BIM2TWIN1. It focuses on describing a digital twin of the construction
phase. The representation of process dependencies is handled similarly to IFC with the so-called
ProcessPrecondition. All four types of sequences are defined as individuals of this class. Regarding
the representation of decomposition criteria, three diferent types of processes are defined. These are
WorkPackage, Activity, and Task (see Figure 4). They resemble the decomposition by production
method, construction step and building element and must be applied in this specific order [
Finally, the Internet of Construction Process Ontology (IOC) is a recent and still ongoing development.
It is dedicated to the definition of construction processes with a wide range of involved objects and
persons. Furthermore, it defines various types of process states [
All of the introduced schemata for process description are ontologies that can be used in the context
of the Semantic Web, initiated by Berners-Lee et al. [
Based on the research gap presented in Section 2.3, an ontology for the representation of construction
schedules was developed. Particular focus is dedicated to diferent types of process decomposition
criteria that are commonly used. For this, the process hierarchies of schedules of various construction
projects are analysed. While in this paper, a new ontology for schedule representation is proposed,
an alternative option would be to integrate the newly defined classes for process preconditions and
decomposition into existing ontologies. Considering the FAIR data-sharing principles, integration
into existing ontologies is favoured [
It is important to note that in the frame of this paper, only processes related to the construction execution are considered. The schedule of the planning phase is out of scope.
Process decomposition criteria play a crucial role in understanding the process hierarchy and dependencies between processes. They describe how the parent process is divided into smaller parts and give insights into the relationship between the diferent child processes. For example, a division of a process by storey creates a spatial dependency of the processes and, therefore, might also imply an order in which the child processes need to be executed. For this reason, explicitly describing these decomposition criteria provides knowledge essential for automated interpretation of the process meaning.
First, construction schedules of eight finished or ongoing construction projects were analyzed regarding the hierarchical structure of the processes and the used decomposition criteria. These sites were pilot sites of the EU Horizon 2020 project BIM2TWIN or active projects of the members of Innovations Management Bau GmbH, an industry partner of the authors. Five diferent construction companies in four countries (Germany, Spain, Finland, and France) are covered. For all of them, a schedule was available in PDF or Excel format, created by the export functionalities of the scheduling software used by the construction company.
All construction processes in the schedules that were divided into sub-processes were manually analyzed regarding the applied criteria for decomposition. The criteria were sorted according to the classification categories presented in Table 1. On the one hand side, some of these categories, like CAD and Information, do not make sense as a process decomposition criterion considering only the construction processes and not the planning phase and were therefore never used in any schedule. On the other hand side, the processes category was divided into production methods and construction steps for more detailed diferentiation. In total, nine decomposition criteria were used in the analyzed schedules. Table 2 gives a complete list with examples for every criterion and the percentage of schedules in which this criterion was used. While eight construction schedules are insuficient to provide a comprehensive list of all criteria for decomposing processes into sub-processes, the authors are confident that the most common ones are covered since the high-level categories of construction classification systems were taken as guidance. All categories identified as meaningful in the context of process decomposition were encountered in at least one of the available schedules.
While many process decompositions can clearly be assigned to a single criterion, some are fitting more than one criterion. As an example, dividing the process that summarizes the indoor works into separate sub-processes, e.g., plumbing, electrical work, painting, and so on, can be seen as a sequence of construction steps or a division of the indoor works by discipline. This depends on the primary intention of the scheduler. While there is no correct and incorrect option, the focus of the decomposition is slightly shifted, in the given example, to the worker crews belonging to diferent domains or to the general sequence in which the processes need to be performed.
A new ontology for process representation was developed based on the identified shortcomings of
existing process schemata. This Construction Scheduling Ontology is a minimal ontology that describes
construction processes with their hierarchical structure, process dependencies, and related concepts.
First, a UML diagram of the schema was developed, which was manually converted into an OWL
ontology using Protégé [
The primary element of the ontology is the process class. Every construction schedule is seen as a list of processes containing basic information like start and end time. The class process decomposition is used to describe the hierarchical structure of processes. This is modelled as a separate class to be able to attach additional information like the criterion for process decomposition. The relationship hasParentProcess and hasChildProcess connect the process decomposition with parent processes and its sub-processes. The decomposition criterion class is used to define the criterion which is used for the decomposition. The ontology defines nine individuals for this class: phase, production method, construction step, location, element, discipline, equipment, material, and property. In this context, the individuals can be understood as an enumeration for the decomposition criterion class. The nine classes correspond with the criteria presented in Table 2. However, these individuals are not represented in the UML in Figure 5. Since it is not allowed to point an object property to a class or a datatype property (source), the name property of the decomposition criterion is used to specify which exact class or property is used to divide a process into several subprocesses. As an example, building elements can be grouped according to their subclass of bot:Element, creating separate processes for walls, columns, slabs, and so on. Another example would be grouping elements according to the value of a specific attribute, e.g., separating load-bearing and non load-bearing walls.
With the class precondition, the dependencies between processes are represented. Four types of process sequences are defined: start-end, start-start, end-start, and end-end. Moreover, the resource class summarizes diferent types of resources that are required for a particular process. This can include construction workers, equipment, materials, and temporary installations like formwork and guardrails. Since existing ontologies already define these resource sub-classes in close detail, only the resource class without sub-classes is defined in CSO, which shall be used as a connection point to other ontologies.
For the representation of building elements and their spatial distribution within specific buildings,
storeys, and rooms, the Building Topology Ontology (BOT) [
While this paper presents a new ontology for construction processes, the classes about process decomposition and dependencies could alternatively be integrated into already existing ontologies. Integration into ifcOWL does not seem suitable due to the significant overhead and missing integration in project management software. However, DiCon, CTO, and IOC are assessed to be suitable to be extended with the missing concepts with relatively little efort. For example, the classes cso:Process and cto:Task and cso:hasTargetElement and cto:isSubjectOf Task can be considered equivalent and form a good starting point for an alignment.
The proposed process model has multiple potential applications. In the context of this study, a methodology for semi-automated linking of building elements defined in an IFC file with individual processes outlined in the construction schedule is introduced. This linkage is facilitated through explicitly defined decomposition criteria, allowing for a predominantly automatic interpretation of the schedule.
Manual linking these elements is highly time-consuming, given that BIM models often comprise several hundreds or even thousands of building elements. Nonetheless, the connection of processes and elements proves valuable, ofering benefits such as enhancing the schedule based on precise quantities extracted from the BIM model and facilitating 4D simulation of the construction process.
To implement the proposed workflow, the construction schedule must be available in an open format like CSV, enriched with additional information about the employed process decomposition criteria. A boolean flag indicating whether the building elements corresponding to the processes are modeled in the IFC model is also required, currently added manually to the schedule. Additionally, the BIM model is required to have access to detailed information about the building elements. Depending on the schedule and the exact use case, information regarding resource assignments might also be needed.
Initiating the workflow involves converting both the IFC model and the schedule into RDF. For the
IFC model, two commonly used converters exist. The IFCtoRDF converter translates the IFC file into an
RDF graph using the ifcOWL ontology. This is suitable when detailed information on the geometry
and attributes of building elements is needed [
The final step involves linking the processes with their corresponding building elements in the RDF graph through the object property cso:hasTargetElement. This is accomplished by an algorithm that traverses each process in the construction schedule according to its hierarchical structure. If the target elements are not represented in the IFC file, the process is skipped, and no element is assigned to it. Conversely, if the target elements are present, the building elements linked to the process’s parent serve as a starting point. Depending on the process decomposition criterion, the algorithm filters out all elements that do not fulfill the criterion, and the remaining elements are then connected to the current process in the RDF graph. In order to match a sub-process with the exact filtering condition, the process name is searched for specific keywords. As an example, when a process decomposition by element type is applied it is searched for words like wall, column, and window to know which process should be assigned with which element type. This is, however, a limitation of this implementation. Table 3 provides an overview of how the linking algorithm handles various types of decomposition criteria.
Check for resources assigned to process with cso:usedResource
Filter by class type of equipment, discipline or material A construction site in Spain was selected as the case study to validate the algorithm’s eficacy in linking the schedule with the IFC file. The utilized IFC file was generated by merging the architectural and structural models provided by the construction company. The construction schedule, devised using the Primavera management software, was exported into Microsoft Excel format. Subsequently, the process decomposition criteria and the boolean flag, indicating the general existence of target elements for each process in the IFC file, were manually added based on the knowledge of planners involved in the project. The construction schedule comprises approximately 90 processes, incorporating decomposition criteria such as phase, construction step, material, element, location, and discipline. A visual representation of the IFC file and a segment of the schedule is presented in Figure 6 and 7.
To implement the linking algorithm detailed in Section 3.3, the C# programming language was
employed. Commencing with the IFC file, the preexisting IFCtoLBD converter was utilized [
The filtering algorithm, as outlined in Section 3.3, has been successfully implemented, featuring distinct functions tailored to handle the diferent decomposition criteria, as detailed in Table 3. To align a specific sub-process with the precise filtering condition, the process name undergoes analysis for specific keywords. For instance, in the case of process decomposition by element type, the algorithm scans for keywords such as "wall," "column," and "window" to determine the appropriate assignment of processes to element types. However, it is crucial to acknowledge a limitation inherent in this implementation. For the processes related to walls, manual intervention was necessary to point the filtering algorithm to the location where the relevant information could be found within the IFC file. In the given case, load-bearing walls had to be distinguished from walls designed for interior partitions. However, in the IFC file, some load-bearing walls were missing the load-bearing property. For this reason, it could not be used to separate the two diferent types of walls correctly. Manual analysis identified that load-bearing walls were assigned a diferent IfcMaterial than the interior partitions. Manually defining that the filtering algorithm should use the material as a distinguishing factor between load-bearing walls and interior partitions for this specific process was suficient to fix the issue. Furthermore, the use of abbreviations in process names poses a challenge for accurate linking. In the frame of the case study, this was resolved by manually replacing abbreviations in the schedule with the complete word.
The outcomes of the linking algorithm are depicted in Figure 8, where building elements linked to the same process share a common color. To enhance clarity, only the leaf processes were considered, preventing elements from being assigned the color of multiple processes. Additionally, the building is separated into the four storeys for visualization purposes.
The availability of additional information about the schedule regarding process decomposition proved beneficial in interpreting the process hierarchy. This supplementary information facilitates a largely automated process interpretation, aiding in identifying relevant processes for specific use cases. For instance, the ability to filter out irrelevant parts of the schedule for a particular simulation based on decomposition criteria streamlines the overall analysis and narrows the focus to pertinent subsections. In the present research, the process interpretation was used for semi-automated linking between processes and building elements. Even though minor manual intervention was required because of cases where it is not immediately clear if certain information is specified in the name, a property or the assigned material of an entity in the IFC file, significant time savings could be achieved.
Several limitations deserve acknowledgment in our study. The efectiveness of the linking processes
is strongly dependent on the quality of the IFC model. Instances of modeling errors, such as elements
erroneously assigned to the wrong storey or lacking material definitions, negatively influence the
accuracy of the results. Furthermore, a certain level of correlation between the schedule and the
IFC model is required. Shared attribute and class names facilitate the linking process, and without
such consistency, full automation becomes challenging. Another limitation involves the granularity
of processes and the BIM model, where disparities may arise. For example, an element described in
the schedule as having multiple parts might be modeled as a single element in the IFC file. While an
algorithm developed by Tulke [
In addressing the challenges surrounding the exchange of project management information within the construction industry, emphasising construction schedules, this research has introduced a novel approach to enhance automation and eficiency. The prevalent reliance on XML or spreadsheet-based ifles for schedule exchange has been identified as a source of information loss and misinterpretation within commonly used project management software. Diverse scheduling practices across construction companies intensify the issue by contributing to a lack of standardisation.
To bridge this gap, the paper proposed a minimal ontology specifically designed to represent construction schedules’ processes, addressing the limitations of existing data schemata. It relies on analysing process decomposition criteria used in eight construction schedules. A small-scale case study showcased the ontology’s application in automated schedule interpretation, highlighting its potential for linking between schedules and corresponding BIM models. This approach reduces manual eforts but also significantly enhances overall eficiency in project management processes. The broader implications of the introduced ontology extend beyond the immediate scope of schedule exchange. The ontology’s versatility ofers opportunities for consistency checks, completeness assessments, and streamlined coordination between contractors and subcontractors.
Future improvements should revolve around the application of natural language processing techniques to improve the interpretation of process names and identify their filtering criteria fully automated. Furthermore, the developed ontology should be fully integrated into existing ontologies after consultation with the corresponding ontology creators to follow the FAIR data principles and ensure that others can apply the developed concepts more quickly. While this study only considered the topmost level of construction classification systems for process decomposition criteria, it should be investigated how considering the complete classification hierarchy could improve automated schedule interpretation.
We thankfully acknowledge Innovation Management Bau for their financial support and for providing us with information about multiple construction projects. Moreover, the research described in this paper received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 958398, “BIM2TWIN: Optimal Construction Management & Production Control”. The authors also thankfully acknowledge the support of the European Commission in funding this project.