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Software evolution relates to how software systems evolve over time. With the emergence of the open source paradigm, researchers are provided with a wealth of data for open source software evolution analysis. In this paper, we present a systematic review of open source software (OSS) evolution. The objective of this review is to obtain an overview of the existing studies in open source software evolution, with the intention of achieving an understanding of how software evolvability (i.e., a software system's ability to easily accommodate changes) is addressed during development and evolution of open source software. The primary studies for this review were identified based on a pre-defined search strategy and a multi-step selection process. Based on their research topics, we have identified four main categories of themes: software trends and patterns, evolution process support, evolvability characteristics addressed in OSS evolution, and examining OSS at software architecture level. A comprehensive overview and synthesis of these categories and related studies is presented as well.

SUMMARYThe literature on the challenges of and potential solutions to architecting cloud-based systems is rapidly growing but is scattered. It is important to systematically analyze and synthesize the existing research on architecting cloud-based software systems in order to build a cohesive body of knowledge of the reported challenges and solutions. We have systematically identified and reviewed 133 papers that report architecture-related challenges and solutions for cloud-based software systems. This paper reports the methodological details, findings, and implications of a systematic review that has enabled us to identify 44 unique categories of challenges and associated solutions for architecting cloud-based software systems. We assert that the identified challenges and solutions classified into the categories form a body of knowledge that can be leveraged for designing or evaluating software architectures for cloud-based systems. Our key conclusions are that a large number of primary studies focus on middleware services aimed at achieving scalability, performance, response time, and efficient resource optimization. Architecting cloud-based systems presents unique challenges as the systems to be designed range from pervasive embedded systems and enterprise applications to smart devices with Internet of Things. We also conclude that there is a huge potential of research on architecting cloud-based systems in areas related to green computing, energy efficient systems, mobile cloud computing, and Internet of Things.

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