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A pattern is an idea that has been useful in one practical context and will probably be useful in others (Fowler, 1997). Transformation patterns identify the correct and reusable solution in transformation implementation and optimize the transformations, too. Similar to patterns such as design and analysis patterns in software engineering, transformation patterns can be used in transformation engineering to improve the quality and efficiency of transformations. Transformation engineering means applying the sound principles of engineering in the implementation of a model transformation (Guerra et al., 2013). Several life cycles are presented in recent research (Bézivin et al., 2003; Siikarla et al., 2008; Lano & Kolahdouz-Rahimi, 2010; Bollati et al., 2013; Guerra et al., 2013), for building the transformation based on engineering methods. These life cycles, that two of the best ones (Bollati et al., 2013; Guerra et al., 2013) are explained in this paper, create a transformation using a methodology that includes several steps, spanning from the specification of transformation to the implementation. However, we can use design, architectural, or specification patterns that are called transformation patterns in different phases of these life cycles, in the same way the software patterns use in the life cycles of software engineering. One important part in using a pattern is recognition of the appropriate pattern based on the structure of the problem. The main goal of this paper is automatic proposition of applicable patterns in the transformation life cycle. The transformation patterns presented in the past (e.g., (Bezivin et al., 2003) or (Iacob et al., 2008)), have introduced only the specification of several patterns. Some of these patterns are formally described in a few papers, but these are not usable in an automatic manner. In fact, developers must use them manually, based on their understanding of the pattern. In addition, these presented patterns are not applied to transformation life cycles; they are just related to one phase of the transformation implementation, e.g., transformation specification or transformation architecture.
In this paper, we present a practical method for automatic pattern proposition in transformation life cycle. The method automatically suggests proper patterns in two phases, i.e., design and implementation phases, of transformation life cycle to the developer of transformation. Proposition of design patterns is based on the structure of transformations while implementation patterns are conducted from the result of applying the other patterns. At each stage, in addition to the proposing the implementation patterns, evaluation of applying suggested patterns can be shown to the developer. As it is demonstrated in the evaluation section, this evaluation is measured based on several metrics, automatically. Evaluation of our method has shown that, for using the patterns in transformation life cycles, it improves the quality of transformation specification and design, modularity, simplicity of transformation, efficiency, as well as decreasing redundancy, duplication, complexity, execution time and memory usage (in many cases). This paper is organized as follows. Next section is dedicated to the related work. Then we explain about the necessity of using the transformation life cycle and introduce two transformation life cycles that are the most complete life cycles which are used in this paper. Subsequently, a transformation pattern is introduced and two patterns as two samples are presented in this section. At this time, we give an overview of our method for pattern proposition in transformation life cycles. Description of our method is structured in two subsections. First, we elucidate the pattern proposition part as the core of our method, and second subsection outlines evaluation part of our method. In this paper, we use a case study to clarify our method. Finally, in the conclusion section we conclude by discussing future work.