In this article, we introduce the Push Tree problem, which exposes the tradeoffs between the use of push and pull mechanisms in information distribution systems. One of the interesting features of the Push Tree problem is that it provides a smooth transition between the minimum Steiner Tree and the Shortest Path problems. We present initial complexity results and analyze heuristics. Moreover, we discuss what lessons can be learned from the static and deterministic Push Tree problem for more realistic scenarios characterized by high uncertainty and changing information request and update patterns.

In this paper we investigate scheduling problems which stem from real-world applications in the chemical process industry both from a theoretical and from a practical point of view.After providing a survey and a general mixed integer programming model, we present some results on the complexity of the process scheduling problem and investigate some important special cases. (We prove the NP-hardness in general and the polynomial solvability for specially structured cases.) Furthermore. we suggest a new heuristic approach and compare this to other heuristics known from the literature.

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