## 1 Introduction
### Research Questions  
To help address these challenges, we have performed a systematic assessment of the documentation of the aforementioned 7 CO frameworks on GitHub with respect to three main software qualities: genericity, maturity and stability. When the documentation appears inconclusive, we rely on experience drawn from earlier run-time experiments with CO frameworks or we have just tested out the specific feature.  
A CO framework is defined as more generic than another when it supports more features than another framework. After all, the more features are supported, the more application and cluster configurations can be supported by a CO framework. The first aim of the systematic assessment is to determine a mapping from CO frameworks to commonly supported features and unique features. In order to provide an easy-to-navigate structure and draw higher-level insights from the results of this systematic assessment, we logically group the found features into 9 functional aspects and 27 sub-aspects that each cover a specific coherent set of related use cases (see Table 1). A functional aspect is defined as a set of related use cases that are of concern to the same type of stakeholder, whereas a functional sub-aspect is defined as an aspect of which the related use cases all represent interactions with the same architectural component or logical substrate of functionality of CO frameworks. We conduct not only a qualitative discussion of the identified aspects and CO frameworks, but also present a quantitative analysis of the number of supported features in each aspect and CO framework.  
We also assess the maturity and stability of the different CO frameworks by studying the historical evolution of these CO frameworks in terms of subsequent releases on GitHub. More specifically, we have inspected all versions that are shown in Figure 2. The aim is to rank CO frameworks with respect to the time when they have released support for a particular feature for the first time. We also study the rate of feature deprecations in the development history to gather a more complete insight in the overall stability of the technological domain and we project this history of feature deprecation to an estimate of feature deprecation risks in the future.  
This systematic assessment with respect to genericity, maturity and stability provides thus answers on the following 10 research questions:  
With respect to genericity:  
* _RQ1. What are the common features of CO frameworks and what are the different implementation strategies for realizing the common features_?
* _RQ2. How can common features be organized in functional (sub)-aspects?_
* _RQ3. What are the unique features of CO frameworks_?
* _RQ4. How are functional (sub)-aspects ranked in terms of number of common and unique features?_
* _RQ5. How are CO frameworks ranked in terms of number of common and unique features_?
* _RQ6. (a) Which functional (sub)-aspects are best supported by a CO framework in terms of highest number of common features? (b) What if unique features are taken into account?_  
With respect to maturity:  
* _RQ7. What is the maturity of a CO framework with respect to a common feature or a functional (sub)-aspect?_
* _RQ8. Which functional sub-aspects are mature enough to consider them as part of the stable foundation of the overall domain? Which CO frameworks have pioneered a particular sub-aspect?_  
With respect to stability:  
* _RQ9. What are the relevant standardization initiatives and which CO frameworks align with these initiatives?_
* _RQ10. What is the risk that common or unique features might become deprecated in the future?_