Hub Covering 问题是一类 Hub Location 问题的子类。其目标是在满足给定起讫点运输任务间路径可达性的前提下，选取一组枢纽节点，以最小化枢纽建设总成本。需满足两个约束条件：每条路径必须恰好包含一个或两个枢纽；且依据具体问题变体，路径总长度或路径中最长边的长度不得超过预设阈值。此类问题广泛应用于城市规划、货运配送系统、航空网络、电信网络及电动出行等领域。尽管 Hub Covering 问题在实践中具有重要意义，但目前尚无对其可近似性的系统性研究：特别是，某些变体之间能否在多项式时间内相互归约仍属开放问题，且此前未有任何近似比结果被证明。本文填补了这一空白，建立了这些变体间的层次关系，证明其中某些变体确为其他变体的特例；对四个变体给出了多项式时间近似算法；对另外八个变体，则证明除非 P=NP，否则不存在可在多项式时间内判定解是否存在的算法。

Hub Covering Problems are a subclass of Hub Location Problems. The objective is to select a set of hubs that enable paths between given origin-destination delivery tasks, while minimizing the total setup cost of the hubs. Two constraints must be satisfied: each path must include one or two hubs, and depending on the problem variant, the total path length or the length of the longest edge must not exceed prescribed limits. Such problems arise in a variety of practical applications, including urban planning, cargo delivery systems, airline networks, telecommunication networks, and e-mobility. Although Hub Covering Problems are especially important from a practical point of view, no systematic study of their approximability exists. In particular, it remains open whether some variants can be reduced to others in polynomial time, and no approximation bound is known. We close this gap by establishing a hierarchy among these problems, demonstrating that certain variants are indeed special cases of others. For four variants, we give a polynomial-time approximation algorithm, and for the other eight variants, we show that no polynomial-time algorithm can decide whether a solution exists unless P=NP.