Heuristics in multi-project scheduling: An Appraisal
Prepared by: Majed Abdeen
Many Project Managers, when thinking about Project Management, consider management of only a single project, but in real life, this is not always the case. What about managing multiple projects simultaneously? There are many methods and models using heuristics in multi-project scheduling, but in my experience in the software sector, I find that using the "Agile Release Planning" scheduling method, is a beneficial alternative method for scheduling for multiple projects, considering each project as an iteration (Epic or Sprint).
In many cases, Project Managers should schedule multiple projects with resources and time limitation, thus, schedules should be evaluated not only in terms of meeting project milestones, but also in terms of the timing and use of limited resources (Meredith et al., 2015, p. 386). I would argue that the use of the Agile (Scrum) process in a multi-project context, with groups working simultaneously on several projects, is one area that would benefit significantly from additional study and research.
Project/Program/Portfolio (PPP) Managers face challenges with scheduling/resource-allocation across multiple-projects. They must consider milestones to be met, resource scarcity, and time constraints for schedules, as resources (human/physical) may be needed simultaneously (Meredith et al., 2015, pp. 386,402). Dealing with resource-allocation/scheduling for multiple-projects is challenging; they are often dealt with as aspects of one larger project (Meredith et al., 2015, p. 402). PPP-Managers must ensure decisions are aligned to the organisation's business-strategy/goals (Laslo, 2010, p. 609). Analytical techniques for dealing with multi-project scheduling do not allow for addressing realistic cases, thus PPP-Managers have turned to heuristics to provide a real-world resolution which considers the complex challenges likely to be faced (Meredith et al., 2015, pp. 403,404).
In multi-project situations, to be successful, PPP-Managers must compromise between time, scope, and cost through continuously applying cost-benefit analysis (Meredith et al., 2015, p. 386). They must decide completion times for tasks/projects, and allocate resources to them, often using a scheduling system to address the key parameters of schedule slippage, resource utilization, and in-process inventory, choosing the one most pertinent to the situation (Meredith et al., 2015, p. 402). Project Managers who have a number of independent teams working on their projects may face similar issues as PPP-Managers, with multi-project scheduling (Wysocki, 2014, p. 479). PPP-Managers may work with project-control-committees to determine projects’ rank, based on importance, which affects scheduling/resource-allocation (Yang & Fu, 2014, p. 167) Projects/activities are interdependent in multi-project scheduling; dependencies may be arbitrary or technological, and PPP-Managers must determine a schedule allowing for resource constraints, activity sequences and permitted durations (Meredith et al., 2015, p. 405).
Early Start Times is a commonly-used heuristic for allocating resources, in which tasks would be listed, ordered by least-to-most slack, and then scheduled in order (Meredith et al., 2015, p. 405). If resources are used prior to scheduling critical activities, borrowing/de-scheduling techniques are used, in which resources are taken from active non-critical tasks, or such a task would be de-scheduled, slowing or stopping the work on that task, respectively (Meredith et al., 2015, p. 406). The benefit of this method is that it is highly straightforward, and thus easily implemented; however, being simplistic it may not address all the inherent complexities, thus PPP-Managers may prefer to choose an alternative method. Additionally, in slowing or stopping critical tasks the project duration will be extended, which may not be permissible.
Master Schedule Model allows for a main project with sub-projects, structured based on responsible teams, in which projects must be integrated through delivery/acceptance points (PMI, 2019, p. 53). To manage/control the schedule for all integrated projects, and the inter-dependencies between projects, a schedule management plan is created (PMI, 2019, p. 53). This method has been demonstrated as beneficial for multi-project scheduling, through benchmarking (Laslo, 2010, p. 609).
Multi-project Model (MPM): Developed based on data acquired through research, this model is designed for an environment comprising multiple-projects with resource constraints (Tsubakitani & Deckro, 1990, p. 80), and is designed to provide both scheduling and monitoring functions. Based on firm data, this model is thus tied closely to real-world situations, which may provide benefits for PPP-Managers who choose to apply it, as they know it is based on applied research rather than a theoretical basis. Further, the model takes the environment into account; different environments require different rules for scheduling (Tsubakitani & Deckro, 1990, p. 82), thus this model provides PPP-Managers with the tailoring they require to ensure efficiency and efficacy.
Milestones can be used by establishing the dependencies between each, in which PPP-Managers plan projects to provide for changes if the project durations cross two-or-more milestones (Pellegrinelli, 1997, p. 147). While less efficient in terms of resource allocation, this method provides the PPP-Manager with more control (Pellegrinelli, 1997, p. 147).
The Resource Schedule Approach developed by Yang combines various approaches and rules to provide a combined method of multi-project resource scheduling. Tested in a real-world case study, this approach enables PPP-Manager to improve their scheduling, as it allows for technology transfers between projects, eliminates problems and uncertainties, and critically, allows for the existing environment (Yang & Fu, 2014, p. 176).
The Critical Chain method uses resource dependencies with the project schedule model activity, and is beneficial for PPP-Manager as it prevents competition for resources prior to projects beginning and provides control through the use of buffers, reducing changes and cost overruns (PMI, 2019, p. 18). Although it may not always provide the level of detail required (PMI, 2019, p. 19), it considers the macro-scale rather than local-scale, and is often thought to be the most beneficial method for dealing with complexity and uncertainty in real-world situations (Yang & Fu, 2014, p. 167).
Successful PPP-Managers are highly skilled in schedule and resource management (Meredith et al., 2015, p. 386); they consider the relationships and inter-dependencies between projects, and are well aware that for multi-project scheduling and resource allocation, "one size does not fit all".
Laslo, Z., 2010. Project portfolio management: An integrated method for resource planning and scheduling to minimize planning/scheduling-dependent expenses. International Journal of Project Management, 28(1), p. 609–618.
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Pellegrinelli, S., 1997. Programme management: organising project-based change. International Journal of Project Management, 15(3), pp. 141-149.
PMI, 2019. Practice Standard for Scheduling. 3rd ed. Newtown Square, Pennsylvania: Project Management Institute, Inc.
Tsubakitani, S. & Deckro, R. F., 1990. A heuristic for multi-project scheduling with limited resources in the housing industry. European Journal of Operational Research, 49(1), pp. 80-91.
Wysocki, R. K., 2014. Effective Project Management: Traditional, Agile, Extreme. 7th ed. Indiana: John Wiley & Sons, Inc.
Yang, S. & Fu, L., 2014. Critical chain and evidence reasoning applied to multi-project resource schedule in automobile R&D process. International Journal of Project Management, 32(1), pp. 166-177.