Complexity and Approximation

Traditionally, the main focus of the information system (IS) literature has been on technical aspects related to system development projects. Furthermore, research in the IS field has mainly focused on co-located project teams. In this respect, social aspects involved in IS projects were neglected or scarcely reported. To fill this gap, this paper studies the contribution of social ties and knowledge sharing to successful collaboration in distributed IS development teams. Data were drawn from two successful globally distributed system development projects at SAP and LeCrov. Data collected were codified using Atlas.ti software. The results suggest that human-related issues, such as rapport and transactive memory, were important for collaborative work in the teams studied. The paper concludes by discussing the implications for theory and suggesting a practical guide to enhance collaborative work in globally distributed teams.

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Social ties, knowledge sharing and successful collaboration in globally distributed system development projects

We consider the problem of establishing minimum-cost multicast connections over coded packet networks, i.e., packet networks where the contents of outgoing packets are arbitrary, causal functions of the contents of received packets. We consider both wireline and wireless packet networks as well as both static multicast (where membership of the multicast group remains constant for the duration of the connection) and dynamic multicast (where membership of the multicast group changes in time, with nodes joining and leaving the group). For static multicast, we reduce the problem to a polynomial-time solvable optimization problem, and we present decentralized algorithms for solving it. These algorithms, when coupled with existing decentralized schemes for constructing network codes, yield a fully decentralized approach for achieving minimum-cost multicast. By contrast, establishing minimum-cost static multicast connections over routed packet networks is a very difficult problem even using centralized computation, except in the special cases of unicast and broadcast connections. For dynamic multicast, we reduce the problem to a dynamic programming problem and apply the theory of dynamic programming to suggest how it may be solved.

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Minimum-cost multicast over coded packet networks

A Protocol Test Generation Procedure.

Chapter 15 – Geometric Shortest Paths and Network Optimization

We obtain the first non-trivial approximation algorithms for the Steiner Tree problem and the Generalized Steiner Tree problem in general directed graphs. Essentially no approximation algorithms were known for these problems. For the Directed Steiner Tree problem, we design a family of algorithms which achieve an approximation ratio of O(k^\epsilon) in time O(kn^{1/\epsilon}) for any fixed (\epsilon < 0), where k is the number of terminals to be connected. For the Directed Generalized Steiner Tree Problem, we give an algorithm which achieves an approximation ratio of O(k^{2/3}\log^{1/3} k), where k is the number of pairs to be connected. Related problems including the Group Steiner tree problem, the Node Weighted Steiner tree problem and several others can be reduced in an approximation preserving fashion to the problems we solve, giving the first non-trivial approximations to those as well.

Approximation algorithms for directed Steiner problems

Approximation Algorithms for Directed Steiner Problems

A timed workflow process model

The fault-state detection approach for blackbox testing consists of two phases. The first is to bring the system under test (SUT) from its initial state to a targeted state t and the second is to check various specified properties of the SUT at t. This paper investigates the first phase for testing systems specified as observable nondeterministic finite-state machines with probabilistic and weighted transitions. This phase involves two steps. The first step transfers the SUT to some state t' and the second step identifies whether t' is indeed the targeted state t or not. State transfer is achieved by moving the SUT along one of the paths of a transfer tree (TT) and state identification is realized by using diagnosis trees (DT). A theoretical foundation for the existence and characterization of TT and DT with minimum weighted height or minimum average weight is presented. Algorithms for their computation are proposed.

To-Yat Cheung

Papers

Approximation algorithms for directed Steiner problems

Approximation Algorithms for Directed Steiner Problems

A timed workflow process model

Optimal transfer trees and distinguishing trees for testing observable nondeterministic finite-state machines

Structure and behavior preservation by Petri-net-based refinements in system design