Abstract
Several real-world problems can be modeled as graph problems. Graph algorithms and theories that have evolved for decades can be applied to solve the problem on hand. Interestingly, many of these graph problems can be solved polynomially, while small changes in a problem definition turn the problem difficult. In this chapter, we explore this path from polynomial network problems to NP-hard ones. Along the chapter, we visit several problems, dedicating more extended discussions to two real-world problems: the weight setting problem, originated from telecommunication networks, and the virtual network embedded problem, a recent stated optimization problem from the computer network area. For these two problems, we discuss their heuristic solution, since only small instances can be solved exactly within a reasonable amount of time.