A solution framework for multi-skilled project scheduling problems with hierarchical skills

Multi-skilled project scheduling concerns the assignment of multi-skilled resources to activities and the scheduling of these activities in order to minimise the project makespan. Since the resources in these problems can be discerned based on their mastered categorical skills, they are considered to be individual entities (human beings) rather than a general class or type of resources. Therefore, researchers have been looking into multi-skilled resources to investigate which other characteristics differentiate them from one another. A main line of research in the last years studies the incorporation of hierarchical skills and their impact on the decision-making in scheduling problems. Hierarchical skills indicate the level at which resources can perform their different skills. In this paper, we present six multi-skilled resource-constrained project scheduling problems with hierarchical skills. In each of these problems, the hierarchical skills have a different impact on the project and its objectives. Solutions are constructed using a solution framework where new problem-specific local searches are embedded in a genetic algorithm. This new framework is tested on existing data from the literature. Computational experiments compare the quality of the solution approaches and the local searches to an integer programming solver. Furthermore, the principal features and tendencies of each problem are discussed. Finally, best-known solutions and lower bounds for all presented problems will be provided.