Rev Rec: A two-layer reviewer recommendation algorithm in pull-based development model

Code review is an important process to reduce code defects and improve software quality. In social coding communities like GitHub, as everyone can submit Pull-Requests, code review plays a more important role than ever before, and the process is quite time-consuming. Therefore, finding and recommending proper reviewers for the emerging Pull-Requests becomes a vital task. However, most of the current studies mainly focus on recommending reviewers by checking whether they will participate or not without differentiating the participation types. In this paper, we develop a two-layer reviewer recommendation model to recommend reviewers for Pull-Requests （PRs） in GitHub projects from the technical and managerial perspectives. For the first layer, we recommend suitable developers to review the target PRs based on a hybrid recommendation method. For the second layer, after getting the recommendation results from the first layer, we specify whether the target developer will technically or managerially participate in the reviewing process. We conducted experiments on two popular projects in GitHub, and tested the approach using PRs created between February 2016 and February 2017. The results show that the first layer of our recommendation model performs better than the previous work, and the second layer can effectively differentiate the types of participation.

Effects of Waxy Maize Relay Intercropping and Residue Retention on Rhizosphere Microbial Communities and Vegetable Yield in a Continuous Cropping System

Intercropping and residue retention contribute to high yield and quality of crops. However, their coupled effects on rhizospheric microbial communities under a continuous vegetable cropping system have not been adequately addressed. The objective of the present study was to assess the effects on soil microbial community and yields of waxy maize（Zea mays L.） intercropped with or without residue retention in a continuous broccoli（Brassica oleracea L.） cropping system, i.e., relay intercropping of broccoli and waxy maize（B/M-B）, relay intercropping of broccoli and waxy maize with residue retention（B/MR-B）, and broccoli monoculture（B-B）. The biomass yields of spring and autumn vegetables in B/MR-B were 16.3%–32.5% and 30.1%–46.1% higher than those of B-B,respectively. Autumn vegetable economic yields of B/MR-B were 28.2%–40.3% higher than B-B. The average well color development followed the order： B/MR-B ＆gt; B/M-B ＆gt; B-B. The Shannon index, Simpson index, and Mc Intosh index were higher in B/MR-B than under monoculture. A principal component analysis showed that microbial communities of B/MR-B soils differed from those of B/M-B and B-B soils. Carbon（C） sources utilized by the rhizosphere microorganisms were mainly carbohydrates, carboxylic acids, amino acids, and polymers; however, the C sources for the soil microbial community differed between intercropping and monoculture. The communities from B/MR-B preferred amino acids and polymers. Available nitrogen（N）, potassium（K）, and phosphorus（P） had an obvious impact on soil microbial community. Additionally, the C source utilization by microorganisms was significantly affected by p H and available K and P. Cropping system diversification through relay intercropping and residue retention effectively improved the functional diversity of the soil microbial communities and increased the yields of vegetables.