Martin Beckmann, Christian Reuter, Andreas Vogelsang
Coexisting graphical and structured textual
representations of requirements
insights and suggestions
Conference Object, Postprint
This version is available at https://doi.org/10.14279/depositonce-6721.
Suggested Citation
Martin Beckmann, Christian Reuter, Andreas Vogelsang (2018): Coexisting graphical and structured
textual representations of requirements: insights and suggestions. - In: Requirements Engineering:
Foundation for Software Quality. - LNCS (10753). - Berlin, Heidelberg: Springer. - ISBN:
978-3-319-77242-4. - pp. 265-280. - DOI: 10.1007/978-3-319-77243-1_1. (Postprint is cited, page
numbers may differ.)
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Co existing Graphical and Structured T extual
Represen tations of Requiremen ts: Insigh ts and
Suggestions
Martin Bec kmann 1 , Christian Reuter 2 , and Andreas V ogelsang 1
1 T ec hnisc he Univ ersit¨ at Berlin, German y
2 Daimler A G, German y
Abstract. [Con text & motiv ation] Man y requiremen ts do cumen ts
con tain graphical and textual represen tations of requiremen ts side-b y-
side. These represen tations ma y b e complemen tary but often times they
are strongly related or ev en express the same con ten t. [Question/prob-
lem] Since b oth represen tation ma y b e used on their o wn, w e w an t
to find out wh y and ho w a com bination of them is used in practice.
In consequence, w e w an t to kno w what adv an tages such an approac h
pro vides and whether c hallenges arise from the co existence. [Principal
ideas/results] T o get more insigh ts in to how graphical and textual re-
presen tations are used in requiremen ts do cumen ts, w e conducted eigh t
in terviews with stak eholders at Daimler. These stak eholders w ork on a
system that is sp ecified b y tabular textual descriptions and UML activ-
it y diagrams. The results indicate that the differen t representations are
asso ciated with differen t activities. [Con tribution] Our study provides
insigh ts in to a p ossible implemen tation of a sp ecification approac h using
mixed represen tations of requiremen ts. W e use these insights to mak e
suggestions on ho w to apply the approac h in a w a y that profits from
its adv an tages and mitigates p otential w eaknesses. While w e dra w our
conclusions from a single use case, some asp ects migh t b e applicable in
general.
Keyw ords: Mo del-Driven Soft w are Sp ecification; Graphical Mo dels; Re-
quiremen ts Do cumen ts; UML Activit y Diagram
1 In tro duction
Eliciting and sp ecifying requiremen ts by means of models is b ecoming more and
more p opular in the dev elopmen t of complex e m b edded systems [1]. Ho w ev er,
these mo dels usually accompan y and complemen t textual requiremen ts and do
not replace them. Therefore, man y requirements documents con tain graphical
and textual represen tations of requirements side-b y-side. This com bined use of
graphical diagrams and textual descriptions is considered b eneficial for the re-
quiremen ts managemen t pro cess [2, 3].
In practice, there are more substan tial reasons wh y the same information
ma y b e expressed in a graphical mo del and also in an accompan ying text. F or
1

example, industrial applications, to ol supp ort, and mo del exc hange for graphi-
cal mo dels are still not standardized [4] and, as a result, man ufacturer/supplier
hando ver is still performed by textual documents. This is especially imp ortant,
since these textual do cumen ts often serv e as the basis for legal considerations
b et w een the contractors [3, 5]. Also, due to differen t backgrounds of the stak e-
holders, not ev ery one is capable of understanding the graphical mo dels [6].
Main taining and up dating information in graphical and textual represen ta-
tions is often p erformed man ually . In previous work, w e ha v e sho wn that this
is a p oten tial source for inconsistencies and quality issues in the requiremen ts
sp ecifications [7]. Moreo v er, b est practices and guidelines for when and ho w to
use graphical or textual represen tations are missing. This leads to discussions
ab out the v alidit y of the represen tations, when deviating represen tations exist.
Without a deep er understanding of ho w the differen t represen tations are
used and wh y they co exist, it is hard to come up with measures for ensuring
consistency or to decide ho w con te n t should b e represen ted. Therefore, w e are in-
terested in ho w co existing graphical and textual represen tations of requiremen ts
are used b y stakeholders of the system. F or this purpose we considered one par-
ticular instance of this case in practice, where a team at Daimler uses UML
Activit y Diagrams to provide a high-lev el o v erview of the activ ation conditions
for a v ehicle function. The information contained in this model is afterwards
transferred in to a tabular textual represen tation that is then further detailed.
W e conducted eigh t in terviews with practitioners at Daimler. Three in tervie-
w ees ha v e dev elop ed the sp ecification approac h describ ed ab o v e. Fiv e in tervie-
w ees work with the resulting requiremen ts do cumen t. F rom these in terviews, w e
deriv e a mo del that describ es for which activities stak eholders use graphical or
textual represen tations. Also, we use the acquired data to pro vide suggestions
on ho w graphical and textual representations should be used to leverage their
p oten tial and a v oid pitfalls which w ould lead to qualit y issues.
Fig. 1: Activity diagram of the function Drive Inhibit
2

2 Bac kground
A team at Daimler emplo ys UML activity diagrams [8] to specify functions of a
system. The diagrams are used to get an early o v erview of the desired function
b eha vior with a sp ecial fo cus on the activ ation of the function, execution condi-
tions, functional paths, and deactiv ation. Fig. 1 depicts a diagram of the system.
The actual b eha vior of the activ ated function is describ ed in the A ction no de la-
b eled with Drive Inhibit (b ottom of the diagram). The activ ation of the function
is describ ed b y a com bination of triggers and c hec ks for conditions. This pattern
to describ e functions is also kno wn for building textual requiremen ts [9]. Ac-
tivit y diagrams are in terpreted according to the requiremen ts-lev el seman tic s of
activities as defined b y Esh uis and Wieringa [10]. As suc h, we assume that eac h
no de executes as so on as a tok en is placed on that no de (b y a transition or b y
o ccurrence of ev en ts). W e also assume that the time required to execute a no de
is infinitely short. Con trol no des hav e the usual seman tics: Mer geNo des (dia-
monds) and JoinNo des (bars) represen t OR connections and AND connections,
resp ectiv ely . All the activit y diagrams of the system are mo deled in a similar
w ay in regard to the used pattern, structure and lay out.
The activit y diagrams are then em b edded in a textual requiremen ts sp ecifica-
tion in t w o representations: (a) graphically as an image, (b) in a tabular, textual
form whic h is supp osed to reflect the same b ehavior as the activit y diagram. The
tabular represen tations may be refined and extended later.
Fig. 2 sho ws the textual representation of the activit y diagram in Fig. 1 as
w e found it in the sp ecification do cumen t of our industry partner. The basic
idea of the textual represen tation is to represent the triggers and c hec king con-
ditions whic h gov ern the execution of a function as a kind of AND-OR table
with p ostfix b o olean op erators. As suc h, the textual representation emphasizes
the prop ositional logic asp ect of the b eha vior. Eac h row represen ts an ob ject,
whic h is des crib ed b y a set of attributes (columns). These attributes are needed
to displa y the relev an t information of the activit y diagram in the requiremen ts
do cumen t. The ID attribute con tains a unique iden tifier of the ob ject. The T ext
attribute is a textual description of the ob ject and is supp osed to b e equal to
the text of the corresp onding elemen t in the activit y diagram. It also contains
the b o olean op erators whic h connect m ultiple elements within a cell or connect
one ro w to the next ro w on the same L evel . The L evel is an attribute to struc-
ture the ob jects hierarc hically . It is deriv ed from the structure of the activit y
diagram. The T yp e attribute denotes whether an ob ject is a function, a trigger
or a condition to b e c hec ked. The ob ject t yp es in the table are deriv ed from the
t yp es of the corresp onding elemen ts in the activit y diagram.
Note that the activit y diagram and the textual represen tation exhibit a n um-
b er of differences with resp ect to b oth placemen t of elemen ts and the sp ecified
b eha vior. E.g., the elemen t Che ck: Engine Cr anking inactive has the predecessor
Che ck: V < 5 km/h in the activit y diagram, while in the textual represen tation
the elemen t V ehicle Ge ar sele ctor is in p osition ”P” is the predecessor. Besides,
some ro ws in the textual represen tation mistak enly ha v e a connector at their
end ( ID 1113 , 1233 ), although there are no further ro ws on the same L evel .
3

These issues ma y originate from the manual generation of the textual represen-
tation and c hanges o ver time. W e ha v e addressed these problems in a previous
pap er [7].
Fig. 2: T extual represen tation of the function Drive Inhibit
The sample in Fig. 2 only depicts the con ten ts deriv ed from the activit y .
Besides the men tioned attributes, the do cument ma y con tain other attributes
used for further dev elopmen t. Also, the textual do cumen t ma y con tain more
detailed information in the form of further requiremen ts and descriptions. These
en tries may be b oth formal (e.g., parameter v alues) and in freely-written natural
language.
3 Related W ork
Graphical notations as a means to ease the understanding of complex systems
ha ve been used in differen t con texts [11, 12]. Nevertheless, despite sho wing se-
v eral adv an tages there are dra wbac ks suc h as end users’ unfamiliarit y with
graphical notations and limits on the displa yable details in visualizations. Mo-
reo ver in requiremen ts engineering, researc h has iden tified the need for differen t
represen tations of requirements [13]. A possibility to tac kle these issues is to use
accompan ying text for graphical mo dels. Arlo w et. al. in tro duced an approach
called Liter ate Mo del ling that w orks with this idea and emplo ys UML mo dels as
the graphical mo dels [6]. This concept of co existing graphical mo dels and tex-
tual descriptions w as pic ked up and discussed for future to ols in requiremen ts
engineering [14]. In addition the approac h is supp orted by ideas using a graphi-
4

cal mo del as a basis to generate a structure for requiremen ts do cuments and
requiremen ts itself [15].
Ho wev er, to the b est of our kno wledge, there is only a small n um b er of
w orks on the topic of ho w to apply the approac h and on its impact. Aside from
computer science, it has b een sho wn that the com bined use of w ords (written
and sp ok en) and pictures has a b eneficial effect on a p erson’s p erception [16].
Still, it is also kno wn that readers fo cus on the represen tation that tak es the
least effort to understand, in case they con tain the same information [17].
A study of Burton-Jones et. al. with studen t participants in v estigates whet-
her a com bination of represen tations is b eneficial [18]. They rep ort a p ositiv e
impact for understanding a new system b y using conceptual graphical mo dels
and a textual narrativ e, but do not give details on ho w to implemen t suc h an
approac h in practice. Our inten t is to impro v e the understanding in this area b y
in terviewing practitioners and to make suggestions on ho w to implemen t suc h a
mixed represen tation approac h in the b est wa y p ossible.
4 Study Design
T o gain a b etter understanding of ho w the approac h is used and ho w the in v olv ed
parties w ork with the activit y diagrams and the textual parts, w e conducted an
in terview study with stakeholders of one particular system. W e designed the
study along the recommendations of Runeson and H¨ ost [19].
Researc h Ob jectiv e: W e wan t to kno w ho w the differen t stak eholders use
the graphical mo dels and the textual descriptions, ho w and where they mak e
c hanges, and how they ensure consistency of the specification. Additionally , we
are in terested in the stak eholder’s p erception of adv antages, c hallenges, and b est
practices of the application of the approac h.
T o reac h this ob jectiv e, we pursue three researc h questions (R Q):
R Q1: F or whic h activities do the stak eholders use whic h represen-
tation? With this researc h question, w e aim at getting insigh ts ab out the use
of differen t representations in order to be able to deriv e suggestions for working
in a setting with co existing represen tations.
R Q2: What are the reasons wh y stak eholders use one or the other
represen tation for sp ecific tasks? W e w an t to find out wh y stak eholders use
one of the represen tations for certain tasks. This is mean t to pro vide insigh ts on
the b enefits the graphical mo dels offer and ho w the co existing artifacts are used
in the w ork of the inv olv ed p ersons.
R Q3: What c hallenges arise in the com bined use of graphical mo d-
els and text and ho w should they b e addressed? W e w an t to kno w what
problems the stak eholders face. This gives us an idea on potentials for impro-
v ement. Also, this R Q is used to deriv e suggestions for the use of graphical
mo dels in com bination with text for sp ecifying functions.
Study Ob ject: W e conducted this study in the con text of the developmen t
of one particular system. The system con tains functions inv olv ed with c harging
the batteries of Plug-in Hybrid Electric V ehicles and Battery Electric V ehicles.
5

As suc h, the system con tains requirements that are relev ant for safet y as w ell as
for usabilit y . Overall, there are 14 functions in the system which are described
b y the approach men tioned in section 2. These functions con tain a total of 22
activit y diagrams and almost 2,000 ob jects (including requiremen ts, descriptions
and headings). The additional activit y diagrams result from the fact that some
subfunctions of the functions are also describ ed b y activit y diagrams and text.
Data Collection: W e conducted in terviews with eigh t stak eholders of one
particular system. The ma jority of the in terview ed stak eholders (fiv e) either
dep end on the con ten ts of the requiremen ts do cument directly or on con ten t
whic h is deriv ed thereof automatically or man ually . The rest of the stak eholders
(three) are concerned with the metho ds that are applied to sp ecify systems
and comp onen ts at Daimler. W e group the participan ts in to three groups: those
in volv ed with the testing of the functions (in the follo wing referred to b y: T 1 ,
T 2 ), those who use the sp ecified functions to sp ecify comp onen ts ( C 1 , C 2 , C 3 ),
and those dev eloping the applied metho ds ( M 1 , M 2 , M 3 ).
The in terviews w ere p erformed b y follo wing an interview guideline. The in ter-
view guideline w as created in multiple iterations. In eac h iteration the structure
and questions w ere refined by discussions with other researc hers and practitio-
ners of our industry partner to ensure that the researc h questions are prop erly
addressed. Ho w ever, the in terviews w ere conducted as op en in terviews. In case
the participan ts mentioned issues aside from the questions of the guideline, w e
did not in terrupt and follo w ed up on these issues in some cases. Also, insights
gained during the in terviews w ere considered in the follo wing in terviews.
The first part of eac h interview concerned the bac kground of the in terview ee.
W e ask ed questions on how long they ha v e b een w orking with the con ten ts of
the system, what their curren t role is, whether there was prior kno wledge in
dealing with graphical mo dels, and what their general attitude is to w ards the
use of graphical mo dels.
The second part aimed at eliciting facts ab out their w ork. This question
co vered what the participan ts actually use the activit y or text for as w ell as in
what w ay the t w o artifacts pro vide differen t information for their tasks. F urther-
more, w e ask ed what purp oses the activit y diagram and the textual description
resp ectiv ely fulfill. As the participan ts M 1 , M 2 and M 3 do not directly work on
the con tents w e engaged them in a discussion ab out their idea ho w the artifacts
are supp osed to b e used. In addition, w e asked the participan ts for their general
impression on the qualit y of the activit y diagrams and the accompan ying text.
The third part aimed at initiating a discussion with the participan ts. W e
w anted to kno w where they see adv antages in the curren t approac h, what c hal-
lenges they face in applying it in their o wn work and ho w to p ossibly deal with
them. W e also w an ted to find out ho w they p erceiv e the influence of the approac h
on the con ten ts they are pro vided with. Hence, w e encouraged the participan ts
to giv e their opinion on the wa y the system’s functions are sp ecified and what
consequences they exp ect for their tasks. F urthermore, w e w an ted to find out
whether they can imagine a differen t pro cess for the sp ecification of functions
and ho w that would differ from the curren t approac h.
6

The ma jority of the in terviews (fiv e) was conducted on site. The rest of the
in terviews (three) was conducted b y telephone. W e ensured that the statemen ts
of the participan ts were handled in an anon ymous w a y to guarantee honest
answ ers. The interviews w ere sc heduled to last ab out an hour. In the end the
shortest in terview lasted 32 minutes, while the longest took almost 90 minutes.
The in te rviews w ere recorded.
Data Analysis: The first author created transcripts of the in terviews . These
transcripts summarize the whole in terview and contain the essen tial statemen ts
of the participan ts. Due to the op en nature of the interviews the n um b er of sta-
temen ts differ from participan t to participant. W e analyzed the transcripts by
applying qualitativ e co ding [20]. The analysis w as performed by the first and the
second author. Our first step w as to read the in terview transcripts to get an o v er-
all impression. This impression w as used to extract a first set of concepts. These
concepts w ere then discussed in regard to their relev ance to w ards the researc h
questions. The discussion resulted in a common set of concepts. W e then c heck ed
the transcripts for information, whic h fit the identified concepts. This task w as
p erformed indep enden tly and afterw ards the co ding w as compared. In case of
deviations the results w ere discussed un til we reac hed a m utual agreemen t. This
m utual agreement led to the omission of a n um b er of statemen ts, since they did
not directly address the researc h questions. It turned out that some of these
omitted statemen ts cov ered in teresting asp ects nonetheless. Hence, it w as deci-
ded to rep eat the pro cess in the same manner with additional concepts in order
to include these asp ects. W e deduced the relev ance of these asp ects b y the fact
that they w ere mentioned b y m ultiple participan ts.
5 Study Results
5.1 Demographics & Bac kground
The in terviewed participan ts ha v e b een w orking for our industry partner for
a time p erio d b et w een 2 and 28 y ears. All of the participan ts stated to hav e
prior exp erience in w orking with graphical mo dels. This encompassed state-
men ts b et ween some familiarit y with UML and similar graphical notations to
exp ert kno wledge in the application of graphical mo dels in the dev elopment of
systems. Also, all participan ts stated to hav e a p ositiv e attitude to w ards the
use of graphical mo dels. Those statemen ts ranged b et w een seeing minor b enefits
to the impression that graphical mo dels are no wada ys necessary to b e able to
comply with standards and to create high-qualit y requiremen ts.
5.2 Benefits & Use of the Approac h
T o address R Q1 and R Q2, w e considered the answ ers to the questions that
concerned the activities the participan ts p erform during their w ork as well as
parts of the discussion rev olving around the adv an tages they p erceiv e.
The tasks the participan ts p erform are shown in Fig. 3. Bo xes denote acti-
vities, while o v als represen t artifacts. The lines sho w the asso ciations that the
7

participan ts mentioned in the in terviews. The arro w b et w een the t w o artifacts
indicates that the graphical mo del is the initial artifact whic h is used to deriv e
the textual descriptions.
R e fin emen t of
R equi r emen t s
Deri vin g T es t
Cases
Gr aph ic al
Mod el
T e x tual
Descriptio n
De v eloping a
G ener al
Under s t a nd ing
Means of
Commun ic a tion
Deri vin g
R equi r emen t s
f or Componen t s
Documen t a tion
of Non -
fun ctional
R equi r emen t s
Pl ann ing

Fig. 3: T asks asso ciated with the artifacts
T o use the graphical mo dels as a means of comm unication and to dev elop a
general understanding w as identified as a task b y almost all participan ts. Addi-
tionally , t wo participan ts ( M 1 , M 3 ) men tioned to use the graphical mo del during
release planning. They use the relations b et ween the elemen ts of the diagram to
gain insigh ts into dep endencies b et w een underlying comp onen ts, whic h in turn
facilitates the planning. The only task asso ciated with b oth represen tations is
deriving test cases. In this matter, participan t T 2 explicitly mentioned that the
activit y diagrams are the actual basis to create some of the test cases and not
just a supp orting alternativ e view of the text.
Nev ertheless, the groups inv olv ed in testing and those resp onsible for com-
p onen ts of the system b oth stated to rely mostly or ev en solely on the textual
description to deriv e their own artifacts (test cases and components require-
men ts). F urthermore the textual description w as men tioned to b e used to refine
requiremen ts and to provide more details on con texts and surrounding circum-
stances b y all of the participan ts.
Aside from the p erformed activities, there seems to b e confusion ab out the
use of the approac h itself. There w as no common understanding b et w een the
participan ts on whether the textual or the graphical represen tation should b e
created first, whic h one is used in case of inconsistencies, and where changes are
incorp orated. Differen t statemen ts w ere made on this topic. Some participan ts
men tioned that they are unaw are of ho w the artifacts are created and where to
incorp orate c hanges.
Moreo ver, the answ ers of the participan ts offered insigh ts on what they think
the artifacts are used for and what b enefits the approac h offers. T able 1 and
T able 2 sho w an ov erview of all statemen ts the participan ts made ab out graphical
8

mo dels and textual descriptions, resp ectiv ely . A 3 denotes that the participan t
made that statemen t while a  denotes that the participants did not mak e
men tion of that fact.
Since all participan ts mentioned to ha v e a p ositiv e attitude to w ards the use of
graphical mo dels, it is not surprising that their use is considered b eneficial. Man y
ev en mentioned that they consider the use of graphical models as a necessity .
As the asso ciated tasks ha ve sho wn, there is a lot of agreemen t that activit y
diagrams are used as a means of comm unication and a basis for discussion. Also,
it w as men tioned explicitly by almost all participan ts that the diagram impro v es
the general understanding of a function.
F or the textual descriptions, most participan ts mentioned that they see the
text as the reference and it is used to pro vide details. The fact that the text
is necessary b ecause of legal considerations w as only mentioned explicitly b y
participan t T 2 . The necessity to support stakeholders who are unfamiliar with
the use of graphical mo dels w as stated b y C 1 , T 2 and M 2 .
5.3 Challenges & P ossible Impro v emen ts
T o answ er RQ3, w e ask ed ho w they p erceiv e the qualit y of the activit y diagrams
and their textual represen tation. More sp ecifically , w e w an ted to kno w ho w they
lik e the w ay the artifacts are structured and whether they face c hallenges b y
main taining co existing artifacts.
All participan ts emphasized that consistency is a ma jor problem in the w ay
the approac h is currently applied. As a consequence, all participan ts w ould ap-
preciate automatic supp ort for deriving the textual description from the activit y
diagrams. They assume that this w ould ha v e a p ositiv e impact on their w ork.
The textual represen tation was criticized with regard to its in terpretation.
Some participan ts said that they would prefer a differen t structure as the curren t
one is not in tuitively understandable. Ho w ev er, further inquiries on this issue
rev ealed that the b o olean op erators without follo wing rows on the same lev el
(describ ed in section 2) are not p erceiv ed as a problem.
Man y issues with the activity diagrams w ere men tioned. F or instance, critique
w as expressed on the depiction of the activity diagrams. This critique focused
most often on the fact that the diagrams are not uniformly designed using the
same to ol. Also, the pattern depicted in Fig. 1 is not strictly enforced. F urt-
hermore, the con tained information was criticized in regard to both the amount
and lev el of detail. This p oin t encompassed differen t opinions of the participan ts.
Some of them stated that required information, suc h as signal names and v alues,
are missing in the diagrams. Others stated that there are to o man y elemen ts and
details in some diagrams to understand a function prop erly . Y et, others said that
the activit y diagrams contain information (e.g., of other components) that is not
relev an t for them.
As the la y out of a graphical mo del has a ma jor impact on its understand-
abilit y [21], we also w an ted an opinion on the qualit y of the la y out. All of the
participan ts mentioned to be satisfied with the quality in that regard. Still, the
w ay the activit y diagrams are em b edded in the to ol w as criticized. The diagram
9

T able 1: Statemen ts ab out the use of graphical mo dels b y participan ts
P articipan t considered
b eneficial
considered
necessary
means of
comm unication /
discussion
impro v es under-
standabilit y
should b e
basis for text
displa y
arc hitecture
represen ts
relations
used for
planning
C 1 3  3 3 3 3 3 
C 2 3  3 3 3  3 
C 3 3  3 3 3 3 3 
T 1 3  3 3 3  3 
T 2  3   3 
M 1  3  3  333
M 2  3 3 3 3 3 3 
M 3  3 3 3   3 3
T able 2: Statemen ts ab out textual descriptions b y participan ts
P articipan t acts as
reference
legal consid-
erations
con tains
details
hando v er for
supplier
used for
non-functional
requiremen ts
supp ort stak eholders
unfamiliar
with mo dels
C 1 3  3   3
C 2 3  3   
C 3 3  3 3  
T 1 3     
T 2  333  3
M 1   3 3  
M 2   3 3 3 3
M 3   3   3
10

is included as a picture in a cell in the requiremen ts do cumen t. Since the default
size of suc h a cell do es not allo w for the displa y of the complete diagram, it is
necessary to adjust its size man ually in order to see the full diagram.
5.4 Bey ond the Researc h Questions
Since w e designed the study as an op en interview, man y things w ere men tio-
ned that did not directly address our researc h questions. Still, some of these
statemen ts are within the scop e of our research ob jective.
Regarding the question what the graphical mo del is used for, the answ er
that app eared most often w as an impro v ed understandabilit y . F urther questions
in that matter rev ealed that the understanding concerns mostly relations b e-
t ween the elemen ts in the graphical represen tation. Asp ects of activities suc h
as indep enden t executabilit y of actions and async hronous b eha vior w ere nev er
men tioned. When we specifically a sk ed for that, it w as stated, that this is of no
imp ortance on that lev el of description.
As the automated generation of the textual description from the graphical
mo dels w as men tioned, w e w an ted to know whether the capabilit y of sync hro-
nization of the graphical and textual represen tation is needed. The participants
answ ered that this capability w ould b e nice-to-ha v e, but all agreed that c hanges
are b est incorp orated in the graphical mo del. M 1 , C 2 and T 2 said, it should not
b e p ossible to c hange asp ects of the graphical mo del in its textual description
and hence a sync hronization in the backw ards direction should not b e allo wed.
T o wards the end of the in terviews, w e c hallenged the approac h as a whole
and ask ed whether they could w ork without the textual represen tation. Because
of the already men tioned uses of the text, ab out half the participan ts instan tly
stated that it do es not seem p ossible. The rest w as op en to the idea, but had
doubts, b ecause of organizational considerations (e.g., hando ver to suppliers,
legal issues) and also stated the necessary mo dels w ould mitigate their main
adv an tage — the capabilit y of offering a clear o v erview. P articipan t T 2 said this
w ould require ma jor mo difications in the compan y structure. It w ould b e p ossible
if all dev elopmen t tasks from suppliers are reintegrated to one place.
6 Discussion
6.1 Findings from our Study
All in all, there seems to b e a common understanding b et ween the differen t
stak eholders on wh y they use this approach and on what to use eac h artifact for.
W e deriv e this conclusion from the fact that all of the stakeholders consider the
t wo coe xisting artifacts to b e at least b eneficial. This is also reflected b y the fact
that there is a high-lev el of agreement to w ards the w a y the resp ectiv e artifacts
are used. F urthermore, the asso ciation of sp ecific tasks with certain artifacts
indicates that b oth the graphical represen tation and the textual represen tation
are necessary to manage the complexit y of to da y’s systems and hence create
high-qualit y requirements sp ecifications.
11

The graphical represen tation is mainly seen as a means of communication
and discussion and for impro ved understandabilit y b y almost all participan ts.
Comm unication and discussions are nece ssary to mak e sure the b eha vior is as
originally in tended. A prop er understanding of the function is mandatory for the
stak eholders. These tw o purp oses facilitate subsequen t tasks suc h as deriving
requiremen ts for comp o nen ts and the man ual generation of test cases. Th us, w e
see the diagram in a rather supp ortiv e role. These results also indicate that the
graphic mo dels are primarily used for the purp ose of visualization and not for
expressing precise seman tics. In consequence it serv es a w allpap er use [22].
The only asp ect that w as commen ted conflictingly ab out the graphical mo d-
els regarded their depiction. P articipant T 1 men tioned, that she w ould rather
prefer more elemen ts in a diagram than scrolling to a different diagram to get
more information. P articipan t T 2 mentioned that the maxim um n um b er of ele-
men ts in a diagram should b e restricted to ab out sev en elemen ts and, if further
elemen ts are required, they should b e nested into a link ed diagram. In addition,
some participan ts complained ab out information in the diagrams that is not
relev an t to them. This conflict cannot b e resolved b y using a single graphical
represen tation of a function for all stakeholders (cf. [13]).
As for the textual represen tation, the results strongly suggest that it is in
fact the preferable medium to accommo date refinemen ts and details. Half of the
participan ts mentioned the need to supp ort stak eholders unfamiliar with graphic
mo dels. This is an issue that constan tly app ears in con texts where mo dels are
used. The co existence of textual descriptions and graphical mo dels app ears to
b e a p ossible solution to this issue [23]. Nev ertheless, there migh t b e more fitting
p ossibilities to arrange the textual represen tation than the one currently used
(see [24] for a study on differen t textual represen tations of activit y diagrams).
Although the graphical represen tation is created as a first step for the sp eci-
fication, its use is not restricted to the sp ecification phase. As our participan ts
p erform a v ariet y of tasks, w e found out that the graphical mo del fulfills more
purp oses than just b eing a starting p oin t for further sp ecification. Amongst oth-
ers it is used to deriv e test cases and to supp ort understanding of the in tended
b eha vior. Hence, it pro ved to ha v e b een a go o d idea to consider participan ts
outside the group of p eople who create the graphical mo dels and textual de-
scriptions. This selection of participan ts, on the other hand, also explains the
lac k of understanding which artifact is created at which step in the process,
where c hanges are incorp orated, and which artifact has to b e used in case of
inconsistencies. In hindsigh t, it turned out that the lack of a definition whic h
artifact is used as the lead is also link ed to the study ob ject. Although half
of the participan ts mentioned that the text is used as a hando v er and for le-
gal considerations, this mainly applies to the deriv ed comp onent specifications.
System sp ecifications are mainly used in ternally and hence using the textual
represen tation as the reference is not strictly enforced.
With regard to these insigh ts w e conclude that in our case using a textual
and graphical represen tation on the sam e lev el of abstraction is an appropriate
means in the dev elopment of systems since the artifacts serv e differen t purp oses.
12

T o mak e the most of the approac h, w e make suggestions that aim at mitigating
the found w eaknesses and taking adv an tages of the iden tified strengths.
6.2 Suggestions
Based on the insigh ts w e mak e suggestions on ho w to implemen t a mixed repre-
sen tations approac h in order to lev erage the p oten tials of the resp ectiv e represen-
tations. F rom the high lev el of agreemen t concerning that the activit y diagram
should b e used as a basis for the text, w e conclude that the activit y diagram is
indeed an adequate starting p oin t for the sp ecification pro cess of our industry
partner. This finding is largely in line with researc h on the use of graphical mo d-
els that emphasizes its use during the early stages of dev elopment [25]. Hence,
this section starts with suggestions on the use of the activit y diagrams and pro-
ceeds with suggestions on the textual represen tation of our industry partner.
Use of the Activit y Diagrams. One of the ma jor factors to the success of
graphical mo dels is that it needs to b e understo o d b y as many stak eholders as
p ossible. T o ac hieve this, it is paramoun t to design the mo dels according to a
defined pattern. Also, w e recommend to use a common to ol for the mo deling in
order to ensure a uniform lo ok, although this migh t b e hard to enforce. Never-
theless, access to the to ol should b e gran ted to all who make use of the activit y
diagram. This is required to address the problem with the handling of the di-
agram. F rom the differen t opinions on the contained information, w e conclude
that a mec hanism is needed to tailor the mo dels according to eac h individual’s
needs. This suggestion has b een stated b efore [13] and is in line with established
solutions on using textual requiremen ts [26].
Use of the T ext. Deriving the text from the activit y diagram av oids incon-
sistencies and hence ensures that the same b eha vior is describ ed b y b oth repre-
sen tations. Aside from the situation of our industry partner, there are already a
n umber of approaches dealing with the generation of requiremen ts sp ecifications
(or parts thereof ) from mo dels [15]. F ollo wing our participan ts the text can b e
used to incorp orate refinemen ts and details. As the complemen tary information
ma y also b e freely written in natural language, this representation ma y in fact
b e b etter suited for stak eholders unfamiliar with the notations of activities. De-
tailed information should only app ear in the text to a v oid further consistency
issues and to guaran tee the main purp ose of the activity diagram is not impaired
— to main tain a high-lev el o verview.
Incorp oration of Changes. As the app earance of c hanges is inevitable in the
course of dev elopmen t, their incorp oration in the artifacts m ust b e considered.
Changes to the relations of en tities are easier to implemen t in the diagram.
F or textual c hanges it do es not mak e muc h difference whic h represen tation is
used. Nev ertheless, to a v oid inconsis tencies only a single artifact should b e used.
13

Hence, the activit y diagram should accommo date c hanges whic h affect b oth
represen tations, although this might be hard to realize considering the fact that
m ultiple p ersons w ork with the sp ecification artifacts. The c hanges in the activit y
diagram are then propagated to the textual represen tation. It has to b e noted
that the additional textual con ten t is not deleted or mo dified in the pro cess.
Alternativ ely , changes could be automatically incorp orated by using tools
suc h as Pro jectional Editors, whic h automatically edit different pro jections of
a common underlying mo del, in this case the activit y diagram and its textual
represen tation. How ev er, this approac h requires substan tial efforts and accor-
dingly trained dev elop ers [27]. Hence, a custom-made and ligh t w eigh t solution
to generate and up date the textual represen tation migh t b e b etter suited for the
situation of our industry partner.
F urther Related T asks. As for the tasks of the resp ectiv e artifacts, the situ-
ation displa yed in Fig. 3 is already a go o d w a y of applying the strengths of the
mo del and the text. The main concern of the graphical mo del is h uman-based
analysis and the exc hange of ideas b et w een stak eholders. As suc h, the tasks of
planning, impro ving understanding, and facilitating communication are prone to
in volv e a visualization. Still, since the graphical represen tation pro vides a high-
lev el ov erview, these tasks are restricted to early stages of dev elopmen t, when
the required descriptions do not need to b e detailed. Nonetheless, the defined
syn tax and seman tics of a graphical mo del can also b e used to automatically
deriv e test cases [28].
6.3 Threats to V alidit y
The participating stak eholders w ere selected b y the second author who is also
activ ely participating in the developmen t of the examined system. W e did not
follo w s p ecific selection criteria, except that participan ts m ust w ork activ ely on
the examined system. Ho w ever, the group of study participan ts only represen t
a subset of all p eople w orking activ ely with the requiremen ts do cumen ts.
F urthermore w e only had access to internal participan ts within one compan y .
Ho wev er, the activit y diagrams and their textual descriptions m ust also b e read
and understo o d outside the compan y , such as legal authorities and suppliers.
Their opinion is critical since inquiries on unclear issues require more effort
b et w een multiple organizations than inside a single compan y .
Also, our study examined the presen t situation of an approach using activ-
it y diagrams. The use of other graphical mo dels migh t influence the prop osed
suggestions as w ell as the b enefits and w eaknesses w e iden tified.
T o answ er our researc h questions, w e only had access to a limited n um b er
of participan ts who actively w ork with this approac h or are resp onsible for the
applied metho ds. Also, w e only gained insights in to a single implemen tation of a
mixed represen tation approach whic h uses activit y diagrams and a v ery sp ecific
kind of textual represen tation. In conclusion, although our findings turned out to
b e consisten t, our results can only b e seen as a first step. Hence, further researc h
is required to generalize our findings.
14

7 Conclusion and F uture W ork
In this pap er, w e presen t the results of a n um b er of in terviews w e conducted
to gain a b etter understanding of a sp ecification approac h that uses co existing
activit y diagrams and tabular textual desc riptions. The results incorp orate an
assessmen t of our participants on whic h artifact is suitable for whic h task as w ell
as their opinion on the b enefits of the resp ectiv e artifacts. The use of graphical
mo dels for themselv es as w ell as their use in co existence with textual description
on the same lev el of abstraction is p erceiv ed as b eneficial. W e use the insigh ts
gained b y these results to deriv e suggestions. The suggestions serv e the purp ose
of pro viding a guideline on how to implemen t suc h an approac h in order to a v oid
inconsistencies and lev erage its full p oten tial.
Although w e think that our results can b e generally applied to approac hes
using co existing graphical and textual artifacts, the results should b e further
v alidated b y rep eating the study with differing implemen tations of the appro-
ac h. The differences might concern the t yp e of graphical mo del and the pattern
for textual description. Also, the exten t to whic h practitioners b enefit from our
suggestions needs to b e further examined. Moreo v er, the graphical and textual
represen tations describ ed in this pap er are not the only artifacts. T o handle
the complexit y of to da y’s systems, further diagrams and asso ciated do cumen ts
migh t b e needed. Ensuring the propagation of necessary changes to these arti-
facts is still not implemen ted in an acceptable manner and hence needs further
in vestigation.
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Why institutions use Plag.ai for originality review, entry 49

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