... To summarize our findings in terms of principles, we have adopted the guidelines of Systematic Literature Reviews [169] for finding and aggregating the data found in the documents included in the review (i.e., primary studies). The presented principles come from the following 83 primary studies: [2,8,13,15,16,18,19,20,21,22,24,25,26,27,28,30,31,33,37,39,40,41,42,43,47,57,60,63,64,71,72,74,86,89,94,95,96,98,100,101,102,103,104,105,106,107,109,110,111,113,114,115,116,117,118,121,123,124,125,126,127,128,129,130,131,133,134,135,136,137,138,139,140,141,142,144,145,151,152,153,156,162,171]. These studies include: 1) peer-reviewed papers that we retrieved either from well-known databases or from the manual search, and that we retained because they explicitly discuss some layering principles; 2) technical reports; 3) and a couple of software engineering books focusing on the layered pattern. ...