Sustainability Quantification in Requirements Informing Design Shola Oyedeji Ahmed Seffah Birgit Penzenstadler Department of Software Department of Software Department of Computer Engineering Engineering Engineering and Computer Science Lappeenranta University of Lappeenranta University of California State University Technology Technology Long Beach Lappeenranta, Finland Lappeenranta, Finland Long Beach, California, USA shola.oyedeji@lut.fi ahmed.seffah@lut.fi birgit.penzenstadler@csulb.edu Abstract— Sustainability has been defined with different the system of software systems? This research aims to serve perceptions and from diverse dimensions making it an different communities, though there is still need to conduct ambiguous concept to objectively engineer and integrate into empirical studies to validate these benefits. Quantifying software development lifecycle. Although a large body of sustainability in software systems will encourage software knowledge already exists on what sustainability is and isn’t, engineering community to develop processes, tools and new little research has explored how to quantify sustainability. How metrics to assess sustainability of software system like the can the definitions and perceptions of sustainability from other quality attributes. It will help companies, organizations software engineering and other fields be turned into and managers to easily adopt and institutionalize requirements, effective measures that quantify sustainability sustainability in their mainstream software development and and most importantly can inform a “sustainability by design” approach? What are the measures and measurement scale of management processes, assess objectively the cost-benefit sustainability? Our long-term research goal is to answer such while creating a business model associated with questions and similar ones. In this position paper, we sustainability of their software system. summarize our investigations and pave the road for a Furthermore, it will guide standardization bodies like theoretical ground of sustainability quantification in software ISO and governmental agencies to enact standards and development and measurement. The goal is to foster research policies for software system sustainability. For example, and standardization initiatives on sustainability as a quality what is the minimum sustainability level of a software attribute and sustainability by design. system to get certain accreditation like we do with security today? It will also make the society and people more aware Keywords: Software Sustainability, Sustainability about the impact of software systems when developing and Requirements, Software Measurement, Software Development, using it; one example is the categorization of a fridge based Sustainability Metrics, Software Design on its level of greenness (energy usage) such as A+, A++. Shall we adopt the same approach in software engineering? I. INTRODUCTION Kocak et al. [5] stated that software development industry is now getting pressure from regulators to consider In a broad sense, sustainability is “the capacity to endure” green certification. As an answer to this pressure, green [1]. In software engineering, sustainability has been attributes of software products should be defined as quality introduced from different dimensions with diverse factor. Then, the biggest challenge facing companies is how perceptions and definitions. Sustainability can be to integrate sustainability into their engineering practices differentiated into several dimensions including when knowing the lack of consensus on what sustainability environmental, human, social, and economic. According to means in software systems and how it can be quantified and Becker et al. [2] sustainability dimensions are interdependent measured. and cumulative - first, second and third order effects from Quantification of sustainability requires that it should be each dimension will bleed into each other. Sustainability considered among the six divisions in ISO standards consideration as a non-functional requirement like security, SQuaRE Model such as: Quality Management Division, usability, reliability can help reduce a software system’s first Quality Model Division, Quality Measurement Division, order impacts which will also aid reduction of second and Quality Requirements Division, Quality Evaluation Division, third-order impacts of software systems. By doing so, SQuaRE Extension Division [6]. By including sustainability developers have the potential to considerably improve in such standardization framework, sustainability may be software systems sustainability from the requirement considered more effectively in the industry. This is not really engineering stage onwards [3]. This also requires measures the case today. One starting point towards this, is to turn the informing how well the development process produces current meanings, perceptions, and beliefs into requirements, sustainable software [4]. factors, measurable criteria and tangible measures. The fundamental question is how to quantify This paper presents the early results of an ongoing sustainability not only for software products, systems and research that aims to build a theoretical ground for services but also for the entire digital ecosystem created by Copyright © 2017 for the individual papers by the papers' authors. Copying permitted for private and academic purposes. This volume is published and copyrighted by its editors. sustainability requirement quantification in software Seacord et al. [11] defined software sustainability as the development. Hopefully, the paper can stimulate a discussion ‘ability to modify a software system based on customer as a means of getting feedbacks for further investigations. needs and deploy these modifications,’ which means The remainder of this paper is as follow. The next section sustainability is the quality of conforming to user provides various sustainability definitions for requirements. specification. Modifiability is the key requirement from this Section III traces the research trends and outcomes from definition. requirement engineering domain. Section IV discusses Harris and Goodwin [2] describe sustainability as system sustainability in software measurement and propose an that must achieve fairness in distribution and opportunity, approach for it. Section V details the proposed approach with adequate provision of social services, including health and an example. Section VI contains the conclusion with remarks education, gender equity, and political accountability and for future work. participation. Their definition focus on social sustainability relating to how well a system can cater for different user II. SUSTAINABILITY DEFINITIONS FOR REQUIREMENT needs irrespective of their condition. The definition The varying definitions of sustainability show there are highlights the requirement for accessibility. diverse opinions about what is sustainability. This makes it Naumann et al. [12] defined sustainable software as harder to define especially when applied to software systems. software whose direct and indirect negative impacts on Still, these definitions provide a basis to start grounding economy, society, human beings, and environment that result sustainability in software engineering research and practices. from development, deployment, and usage of the software Some clarity is needed as to how to quantify sustainability in are minimal and/or which has a positive effect on sustainable software systems in term of quantifiable variables in order to development. Base on this definition the main requirements be able to access and evaluate sustainability of software for sustainability can be derived from the economic, systems. environment, social and individual dimensions of Sustainable software has been viewed from three angles sustainability. [7] as: Table 1 summarizes the most cited definitions and (1) Long lasting software which relates to how well a identifies the key requirements. piece of software will be able to cope with changes; TABLE I. DEFINITION SUMMARY AND REQUIRMENTS (2) Lean software that require less hardware and reduces its own power consumption (energy efficient); Author Definition Requirement (3) Software for sustainable humans as software that Long lasting and Lean Energy efficiency, induces sustainable human behavior. M. R. Idio [7] software, Software for Longevity and User This definition leads to three measurable concerns that sustainable humans Experiences. Sustainability is the we should consider during requirement: energy efficiency, quality of being sustained. longevity and user experiences. Longevity and Venters et al. [8] explore emerging definitions of Venters et al. Longevity and maintenance are the two [8] Maintenance software sustainability from different angles in the field of most important factors for computational science and engineering in order to contribute understanding to the question, what is software sustainability? They stated sustainability Long living system that that in software engineering, longevity and maintenance are should last for more than the two most important factors for understanding Heiko 15 years and can be cost- Longevity and sustainability. Their perception is based on the Oxford Koziolek [9] efficiently maintained and Maintenance English dictionary definition for sustainability ‘the quality of evolved over its entire being sustained’, where sustained can be defined as ‘capable life-cycle. Ability to modify a of being endured’ and ‘capable of being ‘maintained’. software system based on This work highlighted the importance of longevity and Seacord et al. customer needs and Modifiability maintenance for the requirement of sustainability. [11] deploy these Heiko Koziolek [9] define sustainability of software modifications systems from the perspective of software architecture as long Sustainability as system living system that should last for more than 15 years and can that must achieve fairness Harris and in distribution and be cost-efficiently maintained and evolved over its entire Goodwin [2] opportunity, adequate Accessibility life-cycle. This also supports the requirement of longevity provision of social and maintainability. services Tainter [10] introduces sustainability as an active Software whose direct and condition of problem solving, not a passive consequence of indirect negative impacts on economy, society, consuming less resources. To define sustainability in specific Economic, Naumann et human beings, and context the questions should be to sustain what, for whom, al. [12] environment that result environment, social how long and at what cost? Applying Tainter’s definition to and individual from development, software systems, it will help frame definition of deployment, and usage of sustainability into context in order to understand what the the software are minimal boundaries are in a system. Author Definition Requirement research on how best to incorporate management goals and To define sustainability in Sustainability is a requirements in the adoption of sustainability for software specific context the requirement within a system design and development. questions should be to certain context. It Tainter [10] sustain what, for whom, requires the IV. SUSTAINABILITY MEASURES how long and at what specification of the cost? context Sustainability is still not fully explored in the field of software measurement. These are the different works on quantifying sustainability that have been done so far and also III. SUSTAINABILITY IN REQUIREMENT attempts to measure sustainability. ENGINEERING Lami et al. [17] stated there are few studies on ‘what’ The following are some of the research work in the aspects of sustainability to measure and ‘how’ to do it. domain of requirement engineering for sustainability in Calero et al. [18] highlighted that nowadays, sustainability is software systems. a key factor that should be considered in the software quality Raturi et al. [13] focused on how to develop models, though there is less research channeled towards it. sustainability as a non-functional requirement (NFR) using Seacord et al. [11] indicated that planning and management NFR framework informed by sustainability models and how of software sustainment is impaired by a lack of consistently it can be used to correctly obtain and describe sustainability applied, practical measures. Without these measures, it is related requirements of the software system to be developed. difficult to determine the effect of efforts to improve The sustainability model has five dimensions (Human, sustainment practices. Social, Economic, Environmental and Technical Johann et al. [19] presents a generic metric to measure sustainability). software energy efficiency and a method to apply it in Penzenstadler et al. [14] also support the consideration of software engineering process using the formula “Useful sustainability as a nonfunctional requirement like safety and Work Done/Used Energy.” security that are considered as a system quality attribute. Krisztina Erdélyi [20] studies the lifecycle activities of Mahaux et al. [15] highlights the fact that requirements software development with focus on environmental engineering has a major role to play for making software last protection by proposing a formula to calculate software long by reducing the impact of development and disposal waste to encourage the development of green software. phase. Albertao et al. [4] proposed software engineering metrics Roher et al. [16] concerned with the lack of software based on software quality like reusability, portability, engineering teams including environmental sustainability supportability, performance as a way for measuring the during software development proposed the use of sustainability performance of software projects. sustainability requirement patterns (SRPs) as a guide for Bozzelli et al. [21] paper focused on describing and software engineers to elicit sustainability requirements. classifying metrics related to software “greenness” present in Becker et al [3] explains the crucial role of requirements the software engineering literature through systematic not only for software systems but also for how requirement literature review in order to analyze the evolution of those for sustainability can also impact on the social-economic and metrics, in terms of type, context, and evaluation methods natural environment. The two case studies presented by the highlighting metric types like energy, performance, authors’ shows the importance of requirement in utilization, software energy consumption. sustainability design. One of the most referenced model for developing and Based on the above research, there are three major issues measuring sustainable software is the Greensoft Model by for quantifying sustainability during the requirement stage as Naumann et al. [22]. It is a conceptual reference model for seen in the summary in Table I and section III: “Green Software.” The Greensoft model has the objective to support software developers, administrators, and software x First, different research suggests different users in creating, maintaining, and using software in a more definitions, so there is no consensus definition. sustainable way but lacks the clarity and practical examples x Second, the proposed definitions are either too of how this model can be implemented for software system complex or focus mainly a particular dimension of development. The key to measuring sustainability of sustainability. software system requires quantifiable variables that can be applied to all sustainability dimensions in relation to x Third, there is no central framework that is pivotal software system development. to the quantification of sustainability. Thus, a new proposed approach; Sustainable Business Goal Question Metric (S-BGQM) is introduced here. It This shows there is need for discussing and coming to a encourages the incorporation of sustainability during the consensus by researchers interested in sustainability of entire software system development engineering processes. software systems. This can enable development of a central S-BGQM is influenced by work from [23] and [24]. It formwork that would support the addition of sustainability combines results from the software requirement engineering into the SQuaRE Model [6]. We believe this will foster a process [23] into the design and development process. It is focused research towards better quantification of formed by two major components; the Sustainable Business sustainability for software system. It will also encourage Assessment and the Goal Question Metric. Figure 1 portrays S-BGQM. All artefacts in the sustainable business social and environmental perspective represented in assessment component provides support for all activities in business goal, usage goal and system goal [27]. the Goal Question Metric component of S-BGQM. x System Vision: It provides an overview of the In the Sustainable Business Assessment, analysis of whole system and how it interacts with different information in the sustainable business canvas leads to external components and its potential users based creation of sustainability goals. These goals are categorized on the agreement of all stakeholders [28]. into business, usage and system goals with consideration of x Sustainability Analysis: Sustainability analysis sustainability that serve as a requirement for measurement. describe the system from sustainability perspective Based on this categorization, a set of questions are generated by considering sustainability purpose of the system, to characterize all those goals. impact the system has on environment as well as System vision and sustainability analysis provide a quick sustainability goal and constraint of the system [29]. overview of the software system first, second and third order The Goal Question Metric (GQM) component covers the impacts based on those goals. And it provides information following (See Figure 1): useful for specifying the right metric to evaluate the software x Tracing and measurement of system goals based on system. the result from the sustainable business assessment. x Allows software engineers/ managers and company to define questions that can be used to evaluate their software system goals x Choose appropriate metrics that can be used to measure their software system base the questions with consideration of sustainability. These metrics are categorized according the sustainability dimensions as discussed by Raturi et al. [30] and Penzenstadler and Femmer [31] (Economic, Environmental, Social, Individual and Technical Sustainability). Table II portrays metrics and their categorization according to the five dimensions of sustainability. The metrics samples presented in the GQM component give managers simple yardsticks to calibrate how well their company is doing in terms of resource consumption while extracting more value from their processes. The metrics support decision-making by providing a mechanism for benchmarking performance, tracking improvement over time, evaluating products and processes, and developing strategies for improvement. TABLE II. METRIC CATEGORIZATION Category Metric Description Backlog Management index BMI=Number of (BMI) is a workload statement problems for software maintenance. It is close/number of related to both the rate of problems arrival defect arrivals and the rate at *100 which fixes for reported Figure 1 Sustainable Business Goal Metric Process Flow (S- problems become available. BGQM) Technical The total number of functions modified per commit related to The Sustainable Business Assessment component involves adding a new feature/function. the following (See Figure 1): Rework Metric The "extensibility" of a system x Sustainable Business Model Canvas: The Business is generally the ability of the system to tolerate additional Canvas incorporates sustainability considerations features or functionality with during business model design. It allows users to little or no required rework. describe, design, challenge, invent, and pivot their BMI=Number of business model with sustainability consideration problems [25] [26]. close/number of Same as the above BMI x Goal Model: It shows comprehensive and holistic problems arrival Economy *100 goals of the organization or company in relation to The value of the total defects the software under development from the economic, Defect Density= which are known to the size of Total defects/Size the software product Category Metric Description Category Metric Description calculated. failure) The Budgeted Capital - Total Defect Density= Same as the above Defect Net Cost Capital Spent Total defects/Size Density BMI=Number of problems close/number of Same as the above BMI V. S-BGQM PRELIMINARY STUDY BASED ON problems arrival Environment *100 INFORMATION RESEARCHED ONLINE Defect Density= Same as the above Defect The preliminary study described here provides an Total defects/Size Density example of how S-BGQM, as a way of quantifying Useful work done/Used Energy efficiency Energy sustainability works during requirements. A sample project Gateway metric where the project team proposed development of car sharing (1=Task success The amount of successful task system called ShareVoyage for students in City of and 0= Task completed Lappeenranta is presented. It is an online web platform for failure) group shopping and also to share unused foods. Social Defect Density= Same as the above Defect The following seven steps process demonstrate how S- Total defects/Size Density Budgeted hours - Total BGQM works while illustrating the different artifacts such as Net working hours the Sustainable Business Canvas, Goal Model, System vision working hours Gateway metric sustainability analysis of the system and metric worksheet. Same as the above Gateway Individual (1=Task success metric and 0= Task 1. Create Sustainable Busines Canvas. Figure 3 is an example of a canvas created in this study. Figure 2. Sustainability Business Model Canvas (Sustainable Business Assessment) 2. Measurable management goals are created based on 3. All the goals from step 2 are divided into three in the information derived from the sustainable the Goal Model phase show the business, usage and business canvas (see Figure 2). These are the goals system goal of the software system. This division of derived based on the contents from the Canvas : goals serves as a means of proper classification for x Reduce C02 easier measurement after system development. x Encourage car sharing Goal model is the basis for early conflict x Reduce food waste by encouraging food identification and resolution in the system sharing development. Figure 3 shows the details of Goal x Promote sustainable community Model. Figure 3. Goal Model (Sustainable Business Assessment) 4. The Biz Goal from Figure 3 represents the business Encourage car sharing Is there an increase in car sharing among students? goals that have direct impact on the system. The What is the percentage of food waste usage goals are those functional objectives of the Reduce food waste after the application launch? system based on how it should behave. The system Promote sustainable Are students more aware of goals relates to the systems features. The color community Sustainability? semantics in Figure 3 is only used to different each section. Based on the Goal Model (see Figure 3), a 5. System vision created to show the common set of questions is created to characterize each goal. understanding of all the stakeholders including Table II details the questions associated with each users, management staffs, and developers. It is goal. usually a pictorial overview of the system. It portrays how the system functions during operation. TABLE III. SET QUESTIONS (GQM) Goals Questions 6. Sustainability analysis shows the software system Does the application reduce the amount first, second and third order impact as shown in Reduce C02 of carbon emission in Lappeenranta? Figure 4 with consideration for economic, environment, social, individual and technical sustainability dimensions. This analysis is based on economy, process, value and people. It provides a the inputs from step 1 (sustainable business holistic view of how different dimension of canvass) on contents of the environment, society, sustainability impact each other and their relation. Figure 4. Sustainability Analysis (Sustainable Business Assessment) 7. Based on the system vision and sustainability the total software project modules and lines of analysis (see Figure 4) the software development codes. team will be able to generate a metric worksheet (Table III) to evaluate the software system. To clarify, benchmark values are calculated based on TABLE IV. METRIC WORKSHEET (GQM) Question Benchmark Category Metric Value What is the Backlog Management Index BMI=Number of problems close/number of 0 or 100 (BMI)? problems arrival *100 Technical What is the amount of rework? Rework Metric (Total Number of function 0 modified) Question Benchmark Category Metric Value What is the BMI? BMI=Number of problems close/number of 0 problems arrival *100 Economy What is the software defect density? Defect Density= Total defects/Size < 10.46 Does the actual project cost outweigh Positive Number Net Cost budgeted cost? What is the BMI? BMI=Number of problems close/number of 0 or 100 problems arrival *100 What is the defect density? Defect Density= Total defects/Size < 10.46 Environment How much energy does the software Energy efficiency = Useful work done/Used consume? Energy What is the percentage of car sharing? Total amount of rides /100 What is the percentage of food shared? Total amount of food share /100 Can users successfully complete task? Gateway metric (1=Task success and 0= 7 Task failure) What is the software defect density? Defect Density= Total defects/Size < 10.46 Social Are the project teams happy? Net working hours = Budgeted hours - Total Positive number working hours Are the people more aware of Positive number Percentage of food shared sustainability? Can users successfully complete task? Gateway metric (1=Task success and 0= 7 Individual Task failure) What is the software defect density? Defect Density= Total defects/Size < 10.46 The result from Table IV provides a quantifiable result of We identified a set of sustainability requirements from the system measurement from the five sustainability the most cited definitions. This motivated our research on dimensions. It allows for all-inclusive overview of the quantifying sustainability using those requirements. system with traces back the questions that are used to Quantification of sustainability means using variables that characterize each goals during the initial requirement stage. are measures of sustainability. We noticed that the biggest The procedures and steps in S-BGQM encourage major issue is that building a model or framework for sustainability stakeholders to consider sustainability during the software quantification or/and defining its measurement scale and system development. It can be applied to software measures is already a difficult endeavor. The interpretation development life cycle using the enhancement model for of such measures and their validation is a real challenge that sustainable software engineering proposed by Dick et al. requires a long-term research investigations and industry [32]. This model covers sustainability review and preview, experiments. sustainability journal, process assessment and sustainability Without a standard for software sustainability retrospect. requirements, it becomes difficult to identify sustainability S-BGQM does not cover all aspects of sustainability. boundaries. A standard will lead to a unifying consensus that There is still need to improve the methodology used in can foster sustainability quantification in software system. deriving requirements goals from the business assessment S-BGQM is a modest contribution. We do not claim in component. The lack of intermediate stages to transform this paper that S-BGQM is by itself a completed validated sustainability metrics has hinder the ability of S-BGQM to approach or framework. It is a kind of foundation that would provide a better metric categorization. be understood as “showing the map or road about what is need to be done to quantify and measure sustainability”. It’s VI. CONCLUSION not by itself the right and the unique road but it’s just a As highlighted in this paper, researchers have possible one. concentrated their efforts on the definitions and meanings of Our ambition was also to open the doors, or ground the sustainability. Sometimes, definitions are somehow similar efforts in a research agenda on how to measure and often they are contradictory or conflicting. There is not sustainability. However we found that these concerns are yet a general consensus or a common ground on what necessary to overcome the obstacles on this long road for sustainability and software sustainability means and how it building a model for sustainability. The model should be can be quantified objectively. There is an urgent need for the based on a consensus and it can or should be part of ISO entire software engineering community including standards. There is a need for software engineering practitioners and standardization bodies to have a community to create cross-disciplinary research platform, for standardized definition of sustainability, similar to other example building a kind of forum for discussing the software quality factors. This will help to ground it in definitions, perceptions and understanding of sustainability software measurement theories and practices. quantification. That forum can take the form of a new workshop or it can be part of an existing workshop of RE like RE4SuSy or ICSE like the GREENS or it can be a joint 16, no. 1, pp. 5–7, 2014. book that bring people together to discuss it. This paper also [8] C. C. Venters et al., “Software sustainability: The modern tower of babel,” 3rd Int. Work. Requir. Eng. Sustain. Syst. Work. Proc., calls for a forum that brings together all the different vol. 1216, pp. 7–12, 2014. workshops like GREENS, RE4SuSy, GIBSE, and GinSENG [9] H. Koziolek, “Sustainability Evaluation of Software to create a wider consensus. Architectures : A Systematic Review,” Architecture, pp. 3–12, Based on all these investigation, our intention is to bring 2011. this to the workshop discussion community with the hope [10] J. A. Tainter, “Social complexity and sustainability,” Ecol. Complex., vol. 3, no. 2, pp. 91–103, 2006. that it can raise interest among researchers for further [11] R. Seacord et al., “Measuring Software Sustainability,” J. Chem. research on sustainability requirements, quantification and Inf. Model., vol. 53, no. 9, pp. 1689–1699, 2013. measurement. The following are some of the issues awaiting [12] S. Naumann, M. Dick, E. Kern, and T. Johann, “The for further investigations: GREENSOFT Model: A reference model for green and sustainable software and its engineering,” Sustain. Comput. Informatics Syst., vol. 1, no. 4, pp. 294–304, 2011. x How to methodically specify sustainability [13] A. Raturi, B. Penzenstadler, B. Tomlinson, and D. Richardson, requirements, meaning to quantify it? “Developing a sustainability non-functional requirements x How can the sustainability requirements be framework,” Proc. 3rd Int. Work. Green Sustain. Softw. - measured? What are the measurement scales or GREENS 2014, pp. 1–8, 2014. measures for those requirements? [14] B. Penzenstadler, A. Raturi, D. Richardson, and B. Tomlinson, “Safety, security, now sustainability: The nonfunctional x How to categorize the current sustainability requirement for the 21st century,” IEEE Softw., vol. 31, no. 3, pp. metrics and how they related to the five 40–47, 2014. sustainability dimension? [15] M. Mahaux and C. Canon, “Integrating the Complexity of Sustainability in Requirements Engineering,” First Int. Work. Answers to these questions are a major milestone Requir. Eng. Sustain. Syst., 2012. [16] K. Roher and D. Richardson, “Sustainability requirement towards a model of sustainability as a quality attribute. One patterns,” 2013 3rd Int. Work. Requir. Patterns, RePa 2013 - next stage in our research is a survey to explore sustainability Proc., pp. 8–11, 2013. perceptions and practices in industry. [17] G. Lami, F. Fabbrini, and L. Buglione, “An ISO / IEC 33000- Our future work includes carrying out large-scale compliant Measurement Framework for Software Process industrial case studies to identify the practices of Sustainability Assessment,” pp. 50–59, 2014. [18] C. Calero, M. F. Bertoa, and M. Angeles Moraga, “A systematic sustainability in software design and also to test the approach literature review for software sustainability measures,” Green proposed in this paper. The goal is also to understand the Sustain. Softw. ({GREENS)}, 2013 2nd Int. Work., pp. 46–53, ways to integrate and measure software sustainability. 2013. Another work is to study the process of issuing sustainability [19] T. Johann, M. Dick, S. Naumann, and E. Kern, “How to measure and green certification to companies. What are the activities energy-efficiency of software: Metrics and measurement results,” that can be used to improve sustainability practices in the 2012 1st Int. Work. Green Sustain. Software, GREENS 2012 - Proc., pp. 51–54, 2012. industry? One of such certification is the Albert Sustainable [20] K. Erdélyi, “Special factors of development of green software Production Certification [33] and Green Business supporting eco sustainability,” SISY 2013 - IEEE 11th Int. Symp. certification. [34][35]. Intell. Syst. Informatics, Proc., pp. 337–340, 2013. [21] P. Bozzelli, Q. Gu, and P. Lago, “A systematic literature review ACKNOWLEDGMENT on green software metrics,” Sis.Uta.Fi, 2013. [22] S. Naumann, M. Dick, E. Kern, and T. Johann, “The This work is fully supported and funded by DIGI-USER GREENSOFT Model: A reference model for green and - Smart Services for Digitalization platform in Lappeenranta sustainable software and its engineering,” Sustain. Comput. University of Technology (LUT). Informatics Syst., vol. 1, no. 4, pp. 294–304, 2011. [23] B. Penzenstadler, “Infusing green: Requirements engineering for REFERENCES green in and through software systems,” 3rd Intl. Work. Requir. Eng. Sustain. Syst. 2014, vol. 1216, no. 1, pp. 44–53, 2014. [1] B. Penzenstadler, “What does Sustainability mean in and for [24] V. Basili, G. Caldiera, and H. D. Rombach, “Goal Question Software Engineering ?,” 1st Int. Conf. ICT Sustain., 2013. Metric Paradigm,” Encyclopedia of Software Engineering. pp. [2] C. Becker et al., “Sustainability Design and Software: The 528–534, 1994. Karlskrona Manifesto,” Proc. - Int. Conf. Softw. Eng., vol. 2, pp. [25] “3 Minute Introduction to Strongly Sustainable Business Model 467–476, 2015. Canvas, https://prezi.com/k5x2civcaw7y/3-minute-introduction- [3] B. Christoph et al., “Requirements: The key to sustainability,” to-strongly-sustainable-business-model-canvas/ , Accessed on 8- IEEE Softw., vol. 33, no. 1, pp. 56–65, 2016. 06-2017,” no. November, p. 2014, 2014. [4] F. Albertao, J. Xiao, C. Tian, Y. Lu, K. Q. Zhang, and C. Liu, [26] “Strongly Sustainable Business Model Canvas “Measuring the Sustainability Performance of Software Http://www.ssbmg.com/ Accessed on 8-06-2017.” Projects,” 2010 IEEE 7th Int. Conf. E-bus. Eng., pp. 369–373, [27] B. Penzenstadler, “Goal Model Requirements Engineering for 2010. Sustainability,” Lect. slides guest course Softw. Eng. Sustain. [5] S. A. . Koçak, G. I. . Alptekin, and A. B. . Bener, “Evaluation of Lappeenranta Univ. Technol. 2016. Slides available online software product quality attributes and environmental attributes http//birgit.penzenstadler.de/teach/LUT.html. using ANP decision framework,” CEUR Workshop Proc., vol. [28] B. Penzenstadler, “System Vision Requirements Engineering for 1216, pp. 37–44, 2014. Sustainability,” Lect. slides guest course Softw. Eng. Sustain. [6] ISO, “ISO/IEC 25010,” https://www.iso.org/obp/ui/#iso:std:iso- Lappeenranta Univ. Technol. 2016. Slides available online iec:25010:ed-1:v1:en, 2001. http//birgit.penzenstadler.de/teach/LUT.html. [7] M. R. Idio, “Measuring Sustainability Impact of Software,” vol. [29] B. Penzenstadler, “Requirements Engineering for Sustainability - Sustainability Analysis,” Lect. slides guest course Softw. Eng. [32] M. Dick and S. Naumann, “Enhancing Software Engineering Sustain. Lappeenranta Univ. Technol. 2016. Slides available Processes towards Sustainable Software Product Design,” vol. online http//birgit.penzenstadler.de/teach/LUT.html. 2010, pp. 706–715, 2010. [30] Z. Durdik, B. Klatt, H. Koziolek, K. Krogmann, J. Stammel, and [33] Bbc, “albert certification . Available at: R. Weiss, “Sustainability guidelines for long-living software http://www.bbc.co.uk/responsibility/environment/albert-plus.” systems,” IEEE Int. Conf. Softw. Maintenance, ICSM, pp. 517– [34] C. G. B. Network, “Green Business Certification, Available at: 526, 2012. http://www.greenbusinessca.org/.” [31] B. Penzenstadler and H. Femmer, “A generic model for [35] G. B. Bureau, “Green Business Available at : sustainability with process- and product-specific instances,” https://greenbusinessbureau.com/how-gbb-certification-works/,” GIBSE 2013 - Proc. 2013 Work. Green Softw. Eng. Green by no. June, pp. 1–6, 2013. Softw. Eng., no. June 2015, pp. 3–7, 2013.