# Software Architecture for Mobile Cloud Computing Systems
## 4 Frequency, Classification, and Mapping of the Existing Research
### Frequency and Types of Publications  
We discuss the frequency of the research publications during the years (2006 to 2019), illustrated with a bar graph in Figure 3 to answer RQ-1. In Figure 3a, the vertical axis represents the total number of published studies, whereas the horizontal axis represents relative years of publication. For example, in Figure 3a, 'Publication Years' titled 2012 on the horizontal axis represent a total of 15 relevant studies published in the year 2012. Figure 3a also reveals that no research study was published on architectural solutions for MCC before the year 2006 and in 2007. This could be due to the fact that either (i) the literature search did not identify any relevant published research during those years (in Appendix B, Table A1, Step I) or (ii) the studies published during those years did not pass the qualitative evaluation for inclusion in our mapping study (in Appendix B, Table A1, Step II) [25]. As per the guidelines of mapping studies and systematic reviews [14; 15], analyzing the frequency and types of publications provide insights into the quantity and strengths of published research over the years. For example, Figure 3a highlights growth of research in terms of publication frequency, whereas Figure 3b reflects the diversity of published research. Figure 3: An overview of the frequency and type of publications. The graph in Figure 3a suggests that during the years 2006 to 2011, the research on the role of software architecture in MCC systems started to emerge with research focus on exploiting software services (more commonly software as a service (SaaS)) or specifically service-driven architectures for mobile computing [S1; S24; S12]. Please note that the notation [SN] (N is a number) represents a reference to primary studies included in the review in Appendix A. The notation also maintains a distinction between the bibliography and selected literature for mapping study. In the initial six years, we found only a total of nine relevant studies. In those early years, the research proposed solutions that enabled cloud-based servers--offering virtually unlimited computation and storage resources--for (resource-constrained) portable and context-aware mobile devices [S20; S32]. The last eight years (2012 to 2019) reflect a significant and continuous increase in the number of research publications (having 112/121, approximately 92.5% of reviewed studies) with the highest number of published studies in the years 2015 and 2017. The publication growth suggests that in the most recent years, since 2012, the research on the role of software architecture to model, develop, and evolve mobile-cloud systems has been gaining momentum. In these years, architectural solutions have mainly focused on addressing the challenges of offloading the data or code from a mobile device to the cloud server for the _energy efficiency of mobile device_[S4; S10; S51; S65; S94], _real time analytics and computation_[S6; S46; S47; S98], _mobile healthcare services_[S7; S25; S100], and _mobile sensed data collection_[S7; S54; S64] and analysis [S42] on cloud-based servers. A typical example can be the study [S46] that exploits a mobile device as a (front-end) scanner to capture facial images and these images are stored, processed, and recognized in real-time at (back-end) cloud-based server. We further discuss the research challenges and their architectural solution later based on the classification of the research themes. Most recently, solutions are being developed that demonstrate the role of software architecture in architecting mobile cloud-based IoTs [S81; S84; S114], mobile edge computing [S92; S119], and fog computing [S105; S117]. Figure 3 also maintains a distinction between the types of publications that are categorized as _Book Chapters_, _Journal Articles_, _Conference Proceedings_, and _Symposium and Workshop Papers_. We have also provided the reference for the related studies corresponding to each type of publication.