=Paper=
{{Paper
|id=Vol-1216/paper8
|storemode=property
|title=Infusing Green: Requirements Engineering for Green In and Through Software Systems
|pdfUrl=https://ceur-ws.org/Vol-1216/paper8.pdf
|volume=Vol-1216
|dblpUrl=https://dblp.org/rec/conf/re/Penzenstadler14
}}
==Infusing Green: Requirements Engineering for Green In and Through Software Systems==
https://ceur-ws.org/Vol-1216/paper8.pdf
Infusing Green: Requirements Engineering for
Green In and Through Software Systems
Birgit Penzenstadler
University of California, Irvine
Irvine, CA, USA
bpenzens@uci.edu
Abstract—Environmental sustainability can be applied to soft- more sustainable living. Therefore, in our context, sustainable
ware systems in two different understandings — either as green in software is energy-efficient, minimizes the environmental im-
software systems (greening of IT / green IT) or as green through pact of the processes it supports, and has a positive impact
software systems (greening by IT). Currently it is not clear how
environmental sustainability can be systematically supported as on social and/or economic sustainability. These impacts can
an objective in requirements engineering for either of these two occur directly (consumed resources), indirectly (mitigated by
understandings. service), or as systemic effect [23].
This paper presents a checklist and guide word based approach
that demonstrates how to include the objective of environmental Requirements Engineering (RE) is the early phase of soft-
sustainability from the very early steps in finding the stakeholders ware engineering where we determine the exact scope of
and analyzing the domain to the definition of a usage model and the system and iteratively elaborate the stakeholders’ needs
specific requirements. The elaboration is illustrated by a case and concerns [62], [42]. Based on that definition, Require-
study on a car sharing system.
As software systems affect most aspects of our daily lives, ments Engineering for Sustainability (RE4S) [50] denotes the
enabling software engineers to strategically align the objective concept of using requirements engineering and sustainable
of environmental sustainability with the other objectives for the development techniques to improve the environmental, social,
software system under development could considerably decrease and economic sustainability of software systems and their
the impact of people in the industrialized world on the environ- direct and indirect effects on the surrounding business and
ment.
Index Terms—requirements engineering; environmental sus-
operational context. In order to develop such systems, we need
tainability; green through IT; green software systems awareness (by education) and guidance (e.g., as in this paper),
and creativity (to find better solutions). Green Requirements
I. I NTRODUCTION : W HAT IS G REEN R EQUIREMENTS Engineering consequently denotes that same concept with a
E NGINEERING ? specific focus on the direct and indirect environmental impacts
of systems. However, as sustainability is an encompassing
Over the last decades, sustainability research has emerged
concept and one aspect of it cannot be strengthened without
as an interdisciplinary area; knowledge about how to achieve
considering the other dimensions, we will still discuss the
sustainable development has grown, while political action
broader scope of it referring to all five dimensions.
towards the goal is still in its infancy [20], [56].
For a meaningful discussion, sustainability needs to ref- Contribution: Instead of proposing a new framework
erence a concrete system—such as an ecological system, a that might interfere with established practices and be negated
human network, or even a specific software system [54]. by software engineers, as sustainability is only one of many
Software Engineering for Sustainability (SE4S) has developed objectives for a system, we are following an integrative ap-
as a current focus of research due to sustainability being proach. It has been achieved to integrate safety and security as
advocated as major objective for behaviour change on a global additional objectives into requirements engineering [12], [33],
scale [47], [48]. To denote an emphasis on environmental and now we propose to do the same for sustainability [49].
sustainability, the attribute green is widely used. At the same We show that requirements engineering can accommodate the
time, overall sustainability of our daily lives can only occur new objective of improving the environmental sustainability of
when the environmental, social, and economic aspects are in software systems using its current techniques and incorporat-
balance [59]. This has to be reflected in the software systems ing simply a few more instantiations of known requirements
we create. types. An extended version of this paper will be published in
The term Green or Sustainable Software can be inter- a book chapter [7] but we consider it important to get further
preted in two ways: (1) green in software: the software feedback and stimulate discussion at the workshop.
code being sustainable, agnostic of purpose (as in [41]), or
(2) green through software: the software purpose being to Outline: We provide the background, related work and
support sustainability goals, i.e. improving the sustainability foundation in Sec. II, elaborate how to systematically inte-
of humankind on our planet (as in [58]). Ideally, both inter- grate sustainability into RE in Sec. III, discuss the remaining
pretations coincide in a software system that contributes to challenges in Sec. IV, and conclude with an outlook in Sec. V.
II. BACKGROUND Furthermore, Naumann et al. [41] provide a framework for
We lay out the context from sustainability science and Infor- sustainable software engineering. They investigate how web
mation and Communication Technology (ICT) & sustainabil- pages can be developed with little environmental impact, i.e.,
ity, outline related work in RE, and describe the foundation for energy-efficiently, and offer a respective guideline for web
this work: the sustainability dimensions, their requirements, developers. Gu et al. [17] propose a green strategy model
the reference model used for requirements documentation, and that provides decision makers with the information needed to
the case study used for the running example. decide on whether to take “green” strategies and eventually
how to align them with their business strategies. In contrast to
A. Sustainability Science the focus on energy-saving in both of these works, we consider
In general, sustainability is the “capacity to endure”, but a much broader definition of sustainability.
interpreting this concept requires context. A popular definition Cabot et al. [6] report on a case study for sustainability as
of sustainable development was given by the UN as “meeting a goal for the ICSE’09 conference with i*-models to support
the needs of the present without compromising the ability of decision making for future conference chairs. Stefan et al. [53]
future generations to meet their own needs” [59]. Although extend that with quantitative goal modeling techniques. Both
it is not actionable, it is the most cited definition currently works provide model instances for specific case studies while
in use. Ultimately, sustainability depends on the population the work at hand uses a generic model for reference.
at large, so common conceptions of sustainability must be Mahaux et al. [35] present a case study on a business
acknowledged: “People sustain what they value, which can information system for an event management agency and
only be derived from what they know.” [54] For that purpose, assessed how well some RE techniques support modeling of
Joseph Tainter has suggested that it is useful to pose the four specific sustainability requirements. In contrast, our aim is to
questions with regard to sustainability: provide modelling means for integrating sustainability into any
“Sustain what? For whom? How long? At what cost?” [55] software system as a major objective.
More elaborate theoretic frameworks on the definition of D. Dimensions of Sustainability for Software Systems
sustainability exist, e.g. [5], [8], [13], [52], [2], [38], all
referring to systems thinking [37], but are more extensive than Sustainability is characterized by the three dimensions eco-
adequate for the scope of this paper. Sustainability science nomic, social, and environmental [59]. This characterization
is currently discussing whether sustainability is limited by is extended with a fourth dimension human (or individual) by
ecological constraints or enabled by continuous innovation and Goodland [16], portraying individual development by every
transformation [34] and software systems might help in either human over their life time. When analyzing the sustainability
direction. of IT systems, these four dimensions apply, and an additional
dimension, technical, supports better structuring of concerns
B. ICT and Sustainability with respect to software systems. We are convinced that a
The relevance of information and communication technolo- focus on environmental sustainability only makes sense when
gies for environmental sustainability is analyzed by Hilty, Arn- in balance with the other dimensions of sustainability.
falk, Erdmann et al. [23]. On the basis of that, Hilty, Lohmann, Most concisely, the dimension of sustainability are char-
and Huang [20] provide an overview of the fields of ICT acterized as follows [45]: Individual sustainability refers to
in the service of sustainability: Environmental Informatics, maintaining human capital (e.g., health, education, skills,
Green IT, and Sustainable Human-Computer Interaction. As knowledge, leadership, and access to services). Social sus-
technological efficiency alone will not produce sustainability tainability aims at preserving the societal communities in
(cf. Jevon’s paradoxon [29]), sustainable development requires their solidarity and services. Economic sustainability aims at
a combination of efficiency and sufficiency strategies, inter alia maintaining capital and added value. Environmental sustain-
by decoupling economic growth from environmental impacts ability refers to improving human welfare by protecting the
and from the use of natural resources. natural resources: water, land, air, minerals and ecosystem
Furthermore, the newly established conference on ICT for services. Technical sustainability refers to longevity of systems
Sustainability (ICT4S) [22] is establishing a research commu- and infrastructure and their adequate evolution with changing
nity that emphasizes interdisciplinary research across various surrounding conditions.
domains. E. Requirements Types for the Dimensions of Sustainability
C. Related Work: RE and Sustainability For general characteristics of sustainability requirements for
The workshop series on Requirements Engineering for the respective dimensions, we have found the following sub-
Sustainable Systems1 [3], [46] has brought a number of types that are used in other requirements categorizations [51]:
contributions on aspects like goal modeling, energy saving, Environmental: Requirements with regard to resource flow,
complexity, sustainability-enhancing application domains, user including waste management, can be elicited and analyzed by
participation, quality, and eco-aware design. Life Cycle Analysis [19], [1]. Furthermore, impact effects can
be analyzed by environmental impact assessment (EIA). The
1 http://www.ics.uci.edu/∼bpenzens/2014re4susy/ challenge is that usually only first order impacts by a system
are considered, whereas second and third order impacts are reduced version of the model as depicted in Fig. 2. For the
not yet accounted for. full AMDiRE model, please refer to [39].
Individual: Parts of individual sustainability are covered by Green requirements engineering may as well be applied with
privacy, safety, security, HCI and usability as well as personal an activity-based approach though—the choice was taken for
health and well-being, which still needs to be made explicit in illustrative purposes, as the artefact-based approach provides
requirements. An example for this could be that an application an overview that is explicitly structured according to the work
suggests to take a break after a specific amount of working results. That way, the result excerpts can be seen in context
time. with other requirements engineering work results.
Social: A share of social sustainability can be treated via
G. Running example: Car Sharing System
computer supported collaborative work (CSCW [4]) require-
ments, which reflect the interaction within user groups, via In a collaboration with BMW in 2012, we elaborated a
ICT for development (ICT4D [18], [57]) requirements, and case study on the car sharing system DriveNow (partially
via political, organizational, or constitutional requirements, as reported on in [14]). The elicitation was carried out in an
in laws, policies, etc. Still missing are, for example, explicit interview series with the DriveNow project leaders and by
requirements for strengthening community building. performing additional background research on the domains of
Economic: The economic sustainability is taken care of hybrid cars, car sharing business models. The requirements
in terms of budget constraints and costs as well as market basis established in that case study was used for elaborating
requirements and long-term business objectives that get trans- the illustrative examples in the paper at hand.
lated or broken down into requirements for the system under The business model is commercial car sharing for registered
consideration. The economic concern lies at the core of most users with flexible drop-off points for the vehicles on public
industrial undertakings. parking lots. The car sharing system is composed of a web
Technical: The technical sustainability requirements include application for registration, reservation and billing, a car fleet
non-obsolescence requirements as well as the traditional qual- maintained by a service partner where each car is equipped
ity characteristics of maintainability, supportability, reliability, with a meter and a transponder, and a central database.
and portability, which all lead to the longevity of a sys- III. I NFUSING G REEN : E LABORATING G REEN
tem. Furthermore efficiency, especially energy-efficiency and R EQUIREMENTS
(hardware-)sufficiency [21] is part of the technical sustainabil-
ity requirements.
Four of these five dimensions are already supported to a Guiding Questions for Green RE:
considerable extent by traditional software quality character- 1. Does the system have an explicit sustainability purpose?
2. Which impact does the system have on the environment?
istics and requirements can be dealt with. The least support 3. Is there a stakeholder for environmental sustainability?
exists for the environmental dimension. Consequently, we 4. What are the sustainability goals and constraints for the system?
especially need to consider second and third order impacts
in the environmental dimension of software systems.
Fig. 1. Guiding Questions for Green Requirements Engineering
F. AMDiRE: Artefact Model for Domain-independent Re-
Based on the concepts presented in Sec. II, we describe how
quirements Engineering
to elaborate green, sustainable requirements within a generic
The various influences on processes and application do- requirements engineering approach. The guiding questions are
mains make requirements engineering (RE) inherently com- summarised in Figure 1.
plex and difficult to implement. When it comes to defining [Q1] Does the system under consideration have an explicit
an RE reference model, we basically have two options: we purpose towards environmental sustainability? If yes, this can
can establish an activity-based RE approach where we define be analysed in depth. If no, it can be considered whether such
a blueprint of the relevant RE methods and description tech- an aspect is desirable and feasible to add. If, again, that is not
niques, or we can establish an artefact-based approach where the case, then the analysis details the potentials for greening
we define a blueprint of the RE artefacts rather than a blueprint of that IT system (further explored in Q2) instead of greening
of the way of creating the artefacts. In the last six years, we through IT, but depending on the kind of system this might
have established several artefact-based RE approaches, empiri- still lead to considerable improvements of the environmental
cally underpinned the advantages of applying those approaches impact of the system [43]. In case the system is widely used,
in industry, and consolidated the different approaches and that is worth the effort.
established the AMDiRE approach, i.e. the Artefact Model [Q2] Does the system under consideration have an impact
for Domain-independent Requirements Engineering. AMDiRE on the environment? Any system has an impact on the envi-
includes a detailed artefact model that captures the basic ronment, as any system is applied in a real world context of
modelling concepts used to specify RE-relevant information, some kind, which is situated within our natural environment.
tool support, and a tailoring guideline that guides the creation Consequently, it has to be analysed as to what are the direct
of the artefacts [39]. For the purpose of this paper, we use a (first order), indirect (second order), and systemic as well
Context / Environment / Problem Domain Requirements / System / Solution Domain
elicit
Stakeholder Model sustainability
objectives specify Usage Model
sustainable
interaction
S Objectives,
& Goals derive S
find sustainability stakeholders S sustainable
system System Vision
Business Process & vision
S Deployment Requirements
Lifecycle
! Constraints
S & Rules System Constraints
! ! Quality Requirements
Domain Model
! ! Process Requirements
S
elicit refine and deduce
sustainability sustainability S
analyse sustainability of context constraints requirements
Fig. 2. Overview of Content Items and Information Flow for Green Requirements Engineering
as potential rebound effects (third order). This potentially the first piece of information that may explicitly include
includes a very large scope, especially for third order effects, green concerns in the form of supporting business pro-
but systemic thinking [36] facilitates such an analysis process cesses or services. If that is not the case, then there will
and may lead to significant insights. still be elements in the Domain Model that can be related
[Q3] Is there an explicit stakeholder for sustainability? In to sustainability concerns, due to the impacts caused by
case there is an explicit stakeholder who advocates for envi- the system (see Q2). This is denoted by the activity
ronmental sustainability, there is already a significant represen- analyse sustainability of context.
tative who issues objectives, constraints and considerations to • If the business context and application domain lack
support that quality in the system under consideration. In case adequate root elements for a sustainability analysis, the
there is no such advocate, it can be decided to establish such Stakeholder Model may be used as starting point (see
a role. Otherwise, at the very least, a domain expert should be Q3), characterised by the activity find sustainability
established as a representative for sustainability for providing stakeholders. Whichever the system under consideration,
information on applying environmental standards, legislation, the stakeholder model should include a sustainability
and regulations. advocate, at least as representative for legal constraints.
[Q4] What are the sustainability goals and constraints for • In either case — a system with an explicit sustainabil-
the system? Independent of whether the system has an explicit ity concern as well as without such a mission — the
purpose for supporting environmental sustainability or not, Objectives & Goals should feature sustainability as one
there certainly are a number of objectives that pertain to major quality objective (see Q4). This objective should
the different dimensions of sustainability that may be chosen be included in the general reference goal model of a
to apply. For example, a social network might not have an company used as a basis for instantiation for a particular
explicit environmental purpose, but it certainly has objectives system and then refined according to the system specifics.
supporting social sustainability. Furthermore, any system will Apart from eliciting sustainability objectives from the
at least have some constraints with respect to the environment, stakeholders, it is also necessary to elicit sustainability
as stated in Q2. constraints from the domain model for the Constraints
For the description of how to elaborate green requirements, & Rules, which includes sustainability-related constraints
we limit ourselves to a few concepts that are commonly agreed for any kind of systems, for example, environmental
on as content items or information elements for gathering and standards.
refining requirements, all depicted in the overview in Fig. 2. From these different starting points, the sustainability re-
These are Business Processes, Domain Models, Stakeholders, quirements and constraints are propagated throughout the con-
Objectives, Constraints, System Vision, Usage Model, as well tent items in requirements engineering as illustrated in Fig. 2.
as Quality Requirements, Process Requirements, Deployment This includes the activites derive sustainable system vision,
Requirements, and System Constraints. There are a number specify sustainable interaction and refine and deduce sus-
of potential starting points for green requirements engineering tainability requirements. The following sections walk through
with related elicitation and analysis activities as illustrated in these stages and describe the development of the respective
Fig. 2: content items.
• In case there is a relation of the business process of the In the example of the car sharing system, the business
system under consideration to sustainability or environ- model aims at promoting cars as a service (as opposed to an
mental issues (see Q1), the Business Process Model is owned vehicle), but also includes the objective of reducing
environmental impacts by focusing on hybrid cars and by This is especially helpful for finding passive stakehold-
providing a car sharing service. ers who do not have an active interest in issuing own
goals, but whose constraints have to be adhered to, for
A. Analyse Sustainability of Context
example legislative representatives.
Whenever we are faced with a system that has an explicit The example in Fig. 3 illustrates and excerpt of the stake-
contribution to sustainability by either improving our ways holder model for the car sharing system, including the ones
to analyse the environment and reporting feedback, or by that advocate sustainability or serve as domain experts on its
enabling and incentivising sustainable behaviour in its users, various aspects.
we can analyse the contextual elements this related to in
the Business Processes and the Domain Model. Examples
for such systems are the Carbon Footprint Calculator2 , the
Story of Stuff Project3 , or car sharing systems like Zipcar4 or Sustain Car
constrains
Regula
consults tors
DriveNow5 . If there is no explicit purpose for environmental ability
consult
Sharing
System
ant Owner
sustainability, there might still be a purpose for social sustain- produces for competes Legisla
tion
manages for requests
ability, for example different types of local community tools or provides develops consults
City
council
Compe
social networks. Either way the system will cause some kind titors
of impact on the environment, which can span from first order Car
Manufa
Policy
makers
Fleet
impacts to third order impacts. The system environment and cturer
operat
or
Web
service Develo
provider pers
wider context are usually analysed using a Domain Model. Domain
Experts
This can also serve as the basis for a life-cycle analysis [30] QA
Hybrid Billing User
of the system under consideration. engine
dev. Mainte
Archite
Business
Analyst
CSR
nance CRM
For the car sharing system, first order effects are the DB
ct City
Planner
Engine App
Engine Environ
resources that the system itself (the application on different ers
GreenIT
er Coder
ment
Expert
Comm Business
uter User
expert Req
devices and the database) consume. The second order effects Testers Marketi
ng Eng
Joy
Rider
Shop
per
are the resources the car sharing system triggers in its applica-
tion domain, i.e. the cars that are being shared on the road and Fig. 3. Stakeholder Model of the Car Sharing System
that do consume a considerable amount of resources, but at
the same time decrease the overall consumption of resources
through more cars (which would have been used otherwise). C. Elicit Sustainability Objectives, Goals and Constraints
The third order effects might be a decrease in the number The next step is to elicit the sustainability objectives and
of individually owned cars, less parking space shortage, and goals from the stakeholders and to deduce any sustainability
eventually less cars, which would lead to better air quality, but constraints from the business processes and/or the domain
this remains to be observed in the long run. model. A goal is an objective the system under consideration
B. Find Sustainability Stakeholders should achieve [28]. They build a hierarchy, and they can
influence each other in terms of conflicts, constraints, or
Stakeholders are the basis for requirements engineering. support.
They pursue goals, include the users of the system under To facilitate goal elicitation, we distinguish three subcat-
development, and issue constraints [15]. In the context of green egories that refer to different levels of abstraction in sys-
requirements engineering, the goal is to elicit stakeholders tems development: Business Goals are all business-relevant
that advocate for sustainability and that are domain experts (strategic) goals as well as goals with direct impact on the
for life cycle analysis, environmental concerns, legislation for system or project. Usage Goals are a direct relation to the
environmental regulations, or environmental standards. functional context and usage of the system (user perspective)
There are different possible approaches to identifying stake- for behaviour modelling. System Goals are system-related
holders for sustainability [45]: goals that determine or constrain system characteristics [39].
1) Reference list: Instantiating generic reference lists of Each usage goal is related to a business goal and each system
stakeholders for the concrete project context (see [45] goal to a usage goal.
for a generic list of sustainability stakeholders). In order to consider the sustainability perspective during
2) Context: Inspecting the business and operational context goal modelling, we consult a reference model for sustainabil-
of the system under development, and understanding ity, that represents the sustainability dimensions by sets of
which concrete roles are involved. values. Values are approximated by indicators, supported by
3) Goals: Iteratively analysing and refining a generic sus- regulations, and contributed to by activities [44].
tainability model [44] and deducing the related roles. Instantiating the generic sustainability model for a specific
2 http://coolclimate.berkeley.edu/carboncalculator
system is feasible in a case whether sustainability is the major
3 http://storyofstuff.com/ purpose of the system under consideration. For most systems
4 http://www.zipcar.com/ sustainability will be one amongst a number of objectives,
5 http://www.drive-now.com/ therefore it is more suitable to develop one overall Goal Model
for the system and to detail the submodel for the objective very clear in the vision. In case it is a minor aspect, it may
of sustainability by using the sustainability dimensions and still be expressed as one of the concerns.
the generic sustainability model as a reference. This means The system vision defines the system scope and com-
to analyse the generic sustainability model and to decide for prehends the system context (business context as well as
each value within the dimensions whether it is applicable to operational context), which is intended to realise a number of
the system under development and, if so, to select those related Features. A feature is, in our understanding, a prominent or
activities which can be operationalized as goals for the system. distinctive user-recognisable aspect, quality, or characteristic
of a system that is related to a specific set of requirements,
Sustainable
whose realisation enable the feature [9]. Furthermore, it de-
mobility
notes the most important stakeholders and their concerns, in
[economic]
order to serve as communication basis with all stakeholders,
[environmental]
Long-term return
on investment
Minimize
environmental
[social, economic]
Car as a service including non-technical ones. As example, the system vision
impact
for the car sharing system is depicted in Fig. 5. It was
[environmental,
elaborated in discussion with various stakeholders from the
[economic] [individual]
[economic, Transparent
economic]
Save resources Commute respective industry domains (car manufacturer, fleet operator).
technical] pricing model
Easy
maintenance [individual]
[social,economic]
Rent car
Carpool Answer(
[economic, [technical, I(want(to(
customer(
individual] individual] CRM( enquiries.(
Search( minimize(my( Available( Save(costs(
Easy financial Good [social] environmental( &(energy(
navigation Establish impact.(
control
community Complaint( Car(pool(
Share(
I(want(to(
Call(center( drive(from(
[technical] [technical, social] [environmental, [technical]
Good coding Use crowd- technical] High availability A(to(B.(
[social] Support(
practices sourced traffic Use hybrid cars Provide user Register(( Par0cipate(
data (e.g. Waze) forum Adver0se(
[economic, We(want(to(contribute(
Rent(
[technical] technical] [technical] to(sustainable(mobility.(
WebApp(
Clear interface
definitions
Few variables High reliability
of cars
Car(Sharing(Community(
Sustainability?(
System**
Profit?( Data( scope*
Base(
Fig. 4. Sustainability Goals of the Car Sharing Case Study
Rental(
Repor0ng(
In the car sharing example, the objectives in the three Billing(/(
Fill(up(gas,((
clean,((
Sta0s0cs( repair( Return(
categories were elicited by considering the dimensions of Management(
sustainability and how they can be reflected with regard to the High(
availability(
system. Figure 4 depicts an excerpt of the goal model for the Easy(
maintenance(
Service(team/(
Fleet(management(
car sharing system. The overall goal of Sustainable mobility Business*context*
Administra0on( Opera&onal*context*
is broken down into subgoals (e.g. Minimize environmental
impact) and these are refined into usage goals (e.g. Save Fig. 5. The Car Sharing System Vision
resources), which are again broken down (e.g. Carpool) and/or
refined into system goals (e.g. High availability). The square
brackets denote the sustainability dimensions of the goal. E. Usage Model
D. Derive Sustainable System Vision With the system vision established, the next step is to derive
the interaction with the user. The content item Usage Model
The next step is to derive a sustainable System Vision,
details a Use Case Overview in its Use Cases and Scenarios.
a common vision of the system under consideration agreed
We distinguish Services and Use Cases. Both concepts are
upon by all stakeholders that have an active interest in the
means to describe (black box) system behaviour. Use Cases
system. One frequently used method to create system visions
describe sequences of interaction between Actors (realising
that are easy to communicate is Rich Pictures [40]. A rich
user groups) and the system as a whole. More precisely, a
picture is a cartoon-like representation that identifies all the
use case represents a collection of interaction scenarios, each
stakeholders, their concerns, and some of the structural and
defining a set of interrelated actions that either are executed by
conceptual elements in the surrounding work context. The
an actor or by the system under consideration [10]. For each
choice of an easy to understand medium instead of a more
use case, there is at least one Functional Scenario in which
formal and detailed one arises from the need that stakeholders
Actors participate. Use Cases and Scenarios can be represented
of various domains and disciplines have to understand the
in the form of structured text (for example, the Cockburn
vision. The system vision is usually coupled to a milestone
template [10]), in UML use case diagrams, in UML activity
with the scope of an early draft of a common idea of the
diagrams, and in message sequence charts. For the car sharing
system. It can be used as an early basis for estimations and
system we illustrate the example scenario of a commuter user
planning of the subsequent development process. Furthermore,
who wants to carpool.
it is a detection basis for moving targets. In case the purpose of
the system is closely linked to sustainability, this shall become
Example Use Case and Scenario for Carpooling to [60]. Hence, we see a system as a grey box rather than
Primary Actor: Commuter User
Goal in Context: The purpose of this feature is to enable users to carpool, as a glass box, since we restrict systems’ internals, but do
which saves all parties resources. not consider their logical structure by interacting components,
Preconditions: The user is already registered with the system. interface specifications, and functions. They are usually de-
Description:
1) The user logs into the system.
scribed in natural language text.
2) The system displays the user’s dashboard with statistics, offers,
billing, and profile data.
3) The user clicks on the carpool button from the homepage of the Example System constraint for the car sharing system
system. • The web application shall use Waze as navigation system on
4) The system prompts him with a form for entering the carpool handheld devices.
requirements.
5) The user enters his home address, destination, and date & time for Quality Requirements describe the demands for individual
the desired ride. quality attributes across a system’s functionality, the sat-
6) The system displays either the option to select from possible rides
he could add to as a passenger or to offer this ride as a separate
isfaction criteria of those requirements, the qualitative or
new carpooling option. quantitative metrics, and how the metric will be evaluated.
7) The user selects the best available option to add on to an existing They characterise the attributes of the system either coupled
ride as a passenger.
8) The system confirms the ride and informs the driver.
to a specific functionality or as a cross cutting concern.
Variations: They are usually represented in the form of natural text.
7a) The user selects to offer a new ride as carpool. Quality requirements are assessed by Measurements that can
7b) The system acknowledges the new ride and informs the user that the be either a Normative Reference (e.g. a GUI style guide) or
ride will be offered for passengers until 3 hours before departure time.
a Metric. Quality Requirements constrain System Actions and
can be satisfied by Generic Scenarios. We make use of quality
F. Refine and Deduce Sustainability Requirements
definition models as by Deissenböck et al. [11].
Finally, detailed sustainability requirements and constraints
are refined and deduced in four categories: Process Require-
Example High-priority quality requirements for the car sharing system
ments, Deployment Requirements, System Constraints, and
• High availability (economic, individual and social sustainability)
Quality Requirements. Further concerns for the system or the • High usability, easy to use (individual and social sustainability)
project may be managed in a Risk List. • Affordable (individual and economic sustainability)
Process Requirements denote demands with regards to the
The Risk List includes a description of all risks that are
conducted development, for example using a green software
related to project-specific requirements, usually in the form of
engineering process. They constrain the content and / or
natural language text. The conceptualisation of requirements
structure of selected artefact types and the process model, i.e.,
risks is considered on the basis of an artefact model [26], [27].
the definition of the milestones regarding time schedules, used
The risks are implied by the various types of requirements and
infrastructure like mandatory tools, and compliance to selected
we use the risk list as an interface to risk management.
standards and approaches like to the V-Modell XT. They are
mostly described in natural language text.
Example Risk List for the car sharing system
• Peak times and commuting might lead to an accumulation of cars
Example Process Requirement for the car sharing system in specific areas, leading to low availability in other areas.
• Develop the system according to the guidance provided by Software • Excessive usage could cause high energy demands with peaks that
Engineering for Sustainability (SE4S) and as described in the book cannot be satisfied by renewable energy. In that case, more gas
“Green Software Engineering”. would have to be used.
• Users are not active enough, therefore no community would be
Deployment Requirements specify demands with respect to established, and consequently there is no contribution to social
the installation of the system and launching it into operation, sustainability.
for example the migration of the data of the legacy system to
By going through these steps, we have obtained detailed
the green data center used for the system under development.
sustainability requirements that can be traced back to their
respective origins in the Business Process, the Domain Model,
Example Deployment Requirement for the car sharing system the Stakeholder Model, or the Goal Model. From here on, the
• The testing period with the pilot users will be carried out on the responsibility for ensuring that the requirements are designed
server in the Munich Green Data Center.
into the system and eventually implemented moves on from
System Constraints detail restrictions on a system’s tech- the requirements engineer to the system architect and the
nical components and architecture as well as related quality designers.
attributes, for example hardware sufficiency, i.e. that the sys-
tem shall run on the old hardware without resource-intensive IV. D ISCUSSION
upgrades. They describe its functionality by means of single
atomic actions, and its quality by means of assessable system In this section, we reflect on the mapping of sustainability
quality requirements. We consider concepts that describe the dimensions to content items, and discuss requirements con-
transition to logical and technical architecture layers according flicts, cost modeling, legal constraints, and risk management.
A. Which Dimensions Appear in which Content Items? heads, but as legislation has banned the old lightbulbs already
Independent of the applied artefact model, it is interesting in some countries, they will have to be used for now. Resolving
to take a look at the mapping of sustainability dimensions such a conflict for a particular case means to assign weights
to content items. Table I gives a coarse-grained mapping of to each of the goals and prioritise whether the energy saving
requirements content items to the sustainability dimensions is greater or whether the risk and long-term negative impacts
that they contain information from. For example, a system of the dangerous materials are greater.
vision will generally include mainly environmental and social C. Cost Modelling
sustainability aspects (as it abstracts from technical details),
Another aspect worth discussing is the connection between
the system constraints will feature many constraints from
stakeholders, goals, and cost modelling. The stakeholders are
the environmental and technical sustainability dimensions,
made explicit in the goal model by tracing back to the rationale
and the process requirements will include demands from the
of a goal, as the information source (e.g. a domain expert) or
environmental, social, and technical dimension.
the issuer of a goal. With respect to assigning costs to the goals
TABLE I
there is a limitation, as this only makes sense for business
R EQUIREMENTS C ONTENT I TEMS AND THEIR S USTAINABILITY goals, but not for values that cannot be expressed in return on
D IMENSIONS investment. Some goals, for example the protection of the en-
Content Item Sustainability Dimension vironment, do not have monetary value in themselves and their
Stakeholder Model all qualitative value is hard to measure. At the same time, it is
Goals all important to define measures to ensure the realization of these
System Vision mainly environmental and social
Usage Model social and economic goals and to show that the approach can make a difference in
Quality Requirements technical those resulting measures. Consequently, instead of assigning
Deployment Requirements technical costs to the sustainability goals, their contribution to higher
System Constraints environmental and technical
Process Requirements environmental, social and technical causes must be made explicit, for example the contribution
Risk List all to objectives commonly agreed on by governments like the
sustainable development goals from Rio+206 , or the Vision
2050 [61].
B. Sustainability Requirements Conflicts
D. Legal Constraints
In traditional qualities considered during software engi-
As a consequence of the fact that environmental goals have
neering we already face a number of potential conflicts, for
not yet been prioritized sufficiently by the economy, legislation
example between code maintenance and code performance, or
has established a number of environmental regulations that
between the development time and the desired quality of a
companies have to adhere to. These regulations will still
software system. Consequently, the question arises what kinds
be extended in the future, which makes legislation probably
of conflicts exists between the five dimensions of sustainability
the most important stakeholder representing environmental
and their related goals.
sustainability in particular. Individual and social sustainability
The economic dimension aligns with the environmental one
are also taken care of by law, for example by worker’s rights,
in terms of resource savings (energy, materials, waste), but
which are supported and represented by worker unions.
they may conflict when it comes to additional certifications,
It would be interesting to see at which point we need new
building a (environmentally and socially) sustainable supply
laws and a different legislation to make sure that important
chain, and turning to more expensive alternative solutions in
questions of sustainability are incorporated into IT systems.
case they are more environmentally friendly. The reason for
Furthermore, it would be interesting to look at other examples
that is mainly that up to now, the negative environmental
such as functional safety and also to a certain extent security,
impacts that are caused by our economy are hardly charged.
where such laws exist.
Therefore, the goal of environmental sustainability does not
get assigned monetary value but only image value, which is E. Risk Management and Environmental Sustainability
likely to be ranked secondly. These conflicts are also discussed Risks, safety and security all strongly relate to sustainability:
in [44]. risks need to be managed in order to enable sustainability, and
Another potential conflict, at least for some systems, is a safety and security are part of sustainability.
trade-off between energy efficiency and dangerous materials. Safety is part of individual and social sustainability for
This is one potential goal conflict in case energy efficiency preserving human life (no injuries) and environmental (no
would require using more dangerous material. Although not a chemical or other hazardous accidents), but also has aspects
software system in itself, a lightbulb might serve as example: in economic sustainability (a product that is not safe will not
New energy-saving lamps are much more energy-efficient than let a company reach long-term economic goals).
the old light bulbs, but at the same time contain toxic mercury Security is also part of various dimensions, the technical
that imposes a threat when a lamp breaks as well as phenol, one as it is a standard quality attribute for systems, then
naphthalene and styrene. In the case at hand, considerate users
will make sure the lamp is not in close proximity to their 6 http://www.uncsd2012.org/
individual and social (as the users shall be protected), and as ACKNOWLEDGEMENTS
a consequence of that also the economic dimension (insecure
systems will not have market success). I would like to thank Ankita Raturi, Debra Richard-
son, Daniel Mendez, Henning Femmer, Alejandra Rodriguez,
Both of these quality aspects have not been around forever,
Oliver Feldmann, Susanne Klein, Manfred Broy, Daniel
but they were introduced as explicit qualities for software sys-
Pargman, Joseph Tainter, Lorenz Hilty, Bill Tomlinson, Juliet
tems after the first safety hazards and the first security threats
Norton, Marcel Pufal, Coral Calero, Xavier Franch, Wolfgang
occurred. Consequently, we can learn from this development
Lohmann, Martin Mauhaux, and Beth Karlin for helpful and
for systematically incorporating sustainability into software
inspiring discussions as well as Joachim Kolling from BMW
engineering [49].
for supporting the case study. This work is part of the DFG
V. C ONCLUSION EnviroSiSE project under grant number PE2044/1-1.
This paper provided an overview of how green requirements
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