# Integration of Cost and Work Breakdown Structures in the Management of Construction Projects
## 2 Literature Review
### Work Breakdown Structure (WBS)
#### 2.1.1 WBS in the International PM Standards  
In order to achieve the project objectives, the ISO 21500 standard [31] suggests that the WBS must state all project deliverables and break them down into smaller packages. All WBS elements must include identification codes aligned with the configuration management plan. This way, the PM team can control the progress and assign responsible people to each of them. Figure 1: Relationship of the work breakdown structure (WBS) with the project. For the International Project Association (IPMA), the project scope must stipulate what is outside and what is inside (what must be done/achieved) [8]. A good definition of the scope and deliverables ensures that discrepancies are eventually avoided and helps with the project planning. However, projects can be broken down according to different points of view (work distribution, project organization, information, documentation structure, etc.) [32]. The (hierarchical) project structures are key mechanisms for keeping the order and ensuring that nothing important is neglected [33]. The work packages (WPs) are assigned to a resource provider, the work is scheduled, the costs are estimated, and eventually the work is commissioned, controlled and completed. For the PMI [9], the WBS subdivides all project work into components, including its deliverables. The WBS also includes a dictionary, which helps to better organize all necessary work into more-easily-identifiable portions. The decomposition has to be oriented to the deliverables required [34]. In this context, there are at least two main issues when developing a WBS: The level of detail and the decomposition criteria [35]. However, there is no universal rule for establishing the level of detail to be reached. Still, project managers know well that project decomposition requires subdividing the work of all deliverables and components into their most fundamental elements, up to the level at which they represent verifiable products, services, or results [9]. This is because the work contained in the WPs has to be eventually scheduled, resourced, budgeted, risk-assessed, measured, and monitored later. The WBS decomposition can also include information on contracts, quality requirements, and technical references of each element to facilitate the project control. However, the WBS does not sequence the work, nor states their interdependencies. For the Project Management Association of Japan (PMAJ) [36], the focus of the WBS lies on the relationships between processes and work through cooperation and compensation. The documentation required for the elaboration of the WBS is prepared by focusing on the tasks and processes required to achieve the objectives. The objectives, in turn, are stated as the summary of characteristics of the qualitative results expected and the quantitative objectives to be reached. To complete the review of the most common international PM standards, it is necessary to underline the approach of AXELOS (a joint venture created by the Cabinet Office on behalf of Her Majesty's Government and Capita PLC) in its PRINCE2 2017 standard [37]. In it, the product breakdown structure (PBS) is at the project core, not the WBS. The PBS refers to the products to be produced during a plan, but containing just that: Products. The WBS on the other hand, involves the entire work that needs to be completed during a plan, containing just activities. Project managers need to plan the whole project then by breaking down the products or outputs of the project first. Only then, they can break down the activities needed to produce those products. To sum up, the decomposition of the project scope into a WBS (or PBS) includes the processes to define the work and deliverables required by the project (ISO 21500: 2012 [31]). Additionally, by doing so, it also defines the project boundaries (IPMA ICB 4 [8]).