Abstract. Software developers spend most of their time modifying and maintaining existing products. This is because systems, and consequently their design, are in perpetual evolution before they die. Nevertheless, dealing with this evolution is a complex task. Before evolving a system, structural modifications are often required. The goal of this kind of modification is to make certain elements more extensible, permitting the addition of new features. However, designers are seldom able to evaluate the impact, on the whole model, of a single modification. That is, they cannot precisely verify if a change modifies the behavior of the modeled system. A possible solution for this problem is to provide designers with a set of basic transformations, which can ensure behavior preservation. These transformations, also known as refactorings, can then be used, step by step, to improve the design of the system. In this paper we present a set of refactorings and explain how they can be designed so as to preserve the behavior of a UML model. Some of these refactorings are illustrated with examples.

This paper examines how inflation taxation affects resource allocation and welfare in a neoclassical growth model with leisure, a production externality and money in the utility function. Switching from consumption taxation to inflation taxation to finance government spending reduces real money balances relative to income, but increases consumption, labor, capital, and output. The net welfare effect of this switch depends crucially on the strength of the externality and on the elasticity of intertemporal substitution. While it is always negative without the externality, it is likely to be positive with a strong externality and elastic intertemporal substitution. Copyright 2007 The Ohio State University.

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