Past, Present, and Future of 3D Software Visualization

A Systematic Literature Analysis

Richard M¨uller

and Dirk Zeckzer

Information Systems Institute, Leipzig University, Leipzig, Germany

Institute of Computer Science, Leipzig University, Leipzig, Germany

Keywords:

3D, Software Visualization, Systematic Mapping Study, Systematic Literature Review.

Abstract:

The ongoing 2D vs. 3D research debate from information visualization also affects software visualization.

There are many 2D, 3D, and combinations of 2D and 3D visualizations for software representing its structure,

behavior, or evolution. This study contributes ﬁndings to this debate and presents the results of analyzing the

applications of 3D in software visualization with the objectives to outline the state-of-the-art, to reveal trends,

and to identify research gaps. The analysis combined a systematic mapping study to get an overview and

a systematic literature review to gain deeper insights. The relevant papers were identiﬁed by three different

search strategies (manual browsing, keyword, and backward search). Starting with a set of 4386 publications

from the ﬁelds of information and software visualization 155 relevant papers dealing with 2D & 3D or 3D

software visualizations were identiﬁed. These papers were analyzed according to dimensionality, aspect,

year, evaluation method, and application of the third dimension. In a nutshell, the majority of 3D software

visualizations represents the structural aspect, is either evaluated using case studies showing working examples

or not evaluated at all, and applies a 2D layout using the third dimension for displaying software metrics.

1 INTRODUCTION

As a branch of information visualization, software

visualization provides tools and methods to create

representations for structural, behavioral, and evolu-

tionary aspects of software systems (Diehl, 2007).

Comprehensive surveys with numerous visualizations

ranging from 2D to 3D were performed by (Graˇcanin

et al., 2005), (Teyseyre and Campo, 2009), and

(Caserta and Zendra, 2011). However, as in its

parental discipline, there is an ongoing 2D vs. 3D

debate. This study aims at investigating the use of

3D in software visualization and how its usefulness is

evaluated.

A suitable approach for this investigation are sys-

tematic mapping studies and literature reviews. A

systematic mapping study aims at building a classi-

ﬁcation scheme in order to structure a research ﬁeld

(Petersen et al., 2008). The scheme comprises facets

detailed by categories. The different facets are com-

bined to answer speciﬁc research questions. The re-

sults include frequencies of publications for each cat-

egory within this scheme. The systematic literature

review focuses on a deeper analysis of the publica-

tions and can have other goals (Brocke et al., 2009).

(Petersen et al., 2008) argue that both methods can be

applied complementary. Thus, we used the mapping

study to gain an overview of the ﬁeld and investigated

speciﬁc questions using detailed reviews.

The major contributions of this state-of-the-art re-

port in 3D software visualization are answers to the

following questions:

• Venue: Where were papers about 3D software vi-

sualization published?

• Aspect: Which aspects of software are visualized?

• Evolution: How did the topic evolve over the last

22 years?

• Evaluation: How was the usefulness of the 3D

software visualizations evaluated?

• Application: How was the third dimension used?

On the basis of these answers trends were revealed

and research gaps identiﬁed.

Müller R. and Zeckzer D..

Past, Present, and Future of 3D Software Visualization - A Systematic Literature Analysis.

DOI: 10.5220/0005325700630074

In Proceedings of the 6th International Conference on Information Visualization Theory and Applications (IVAPP-2015), pages 63-74

ISBN: 978-989-758-088-8

 2015 SCITEPRESS (Science and Technology Publications, Lda.)

2 RELATED WORK

Important prior work ranges from meta-studies and

surveys to literature reviews as well as a mapping

study in the ﬁeld of software visualization.

Hundhausen conducted two meta-studies, one

about software visualization effectiveness (Hund-

hausen, 1996) and one about algorithm visualization

effectiveness (Hundhausen et al., 2002). The classiﬁ-

cation of the evaluation methods into anecdotal, ana-

lytic, and empirical is taken from these studies.

(Graˇcanin et al., 2005) provide a general overview

over software visualization outlining several research

directions, such as (distributed) virtual environments

and visualization metaphors. (Teyseyre and Campo,

2009) give a comprehensive overview over 3D soft-

ware visualization including visual representations,

interaction issues, evaluation methods, and develop-

ment tools. (Caserta and Zendra, 2011) focus on static

aspects of software visualization in 2D and 3D. We

used all three surveys as a starting point for the back-

ward search to ﬁnd relevant papers not covered by the

selected workshops and conferences in our primary

studies.

(Kienle and M¨uller, 2007) identiﬁed quality at-

tributes and functional requirements for software vi-

sualization tools to support researchers using a liter-

ature review. (Schots and Werner, 2014) examined

software visualizations with regard to reuse based

on the task oriented taxonomy from (Maletic et al.,

2002). The complete review can be found here

(Schots et al., 2014). (Seriai et al., 2014) investi-

gated the state-of-the-art in validation of software vi-

sualization tools with a mapping study. The primary

categories of the evaluation method facet are taken

from this study. The main difference to our study is

the focus: we concentrate on 3D software visualiza-

tions includingall aspects, such as structure, behavior,

and evolution. In this context, we investigate publica-

tion locations, evaluation methods, the development

of this speciﬁc ﬁeld over time, as well as the applica-

tion of the third dimension.

3 METHOD

For this study, a hybrid approach was applied combin-

ing a systematic mapping study (Petersen et al., 2008)

with a systematic literature review (Brocke et al.,

2009). First, a mapping study was performed to get an

overview and to answer the ﬁrst four research ques-

tions. Second, a detailed literature review was con-

ducted to answer the ﬁfth research question. Finally,

the results of both processes are summarized in the

ﬁndings. The complete process is depicted in Figure

1. Its steps will be described in the subsequent sec-

tions.

3.1 Deﬁne Scope & Research Questions

We describe the scope of this study according to

Cooper’s taxonomy of literature reviews (Cooper,

1988). The focus lies on applications of 3D

software visualizations. Our goal is to inte-

grate ﬁndings from publications of different work-

shops/conferences/journals to create a comprehensive

view of this topic. The study is organized conceptu-

ally guided by a classiﬁcation scheme. Further, we

adopt a neutral perspective. The main audience are

specialized scholars from the ﬁelds of information vi-

sualization and software visualization. The coverage

is aimed to be representative as we combine man-

ual browsing through relevant workshop and confer-

ence proceedings, a keyword search, and a backward

search starting with state-of-the-art-papers.

With this study, we want to investigate the follow-

ing research questions:

• RQ1: Which workshops/conferences/journals in-

clude papers on 3D software visualization?

• RQ2: Which aspects of software (structure, be-

havior, evolution) are visualized with 3D?

• RQ3: How did 3D software visualization evolve

over the last 22 years and what are current trends?

• RQ4: How is the usefulness of the proposed 3D

software visualizations evaluated?

• RQ5: How is the third dimension used?

3.2 Conceptualize Topic

For the classiﬁcation scheme, a top-downand bottom-

up approach were applied. We started with estab-

lished deﬁnitions from literature for the classiﬁca-

tion of the relevant papers. If a paper introduces a

new category, the corresponding facet in the classiﬁ-

cation scheme was extended. In this study, the fol-

lowing facets are important: dimensionality, aspect,

year, evaluation method, and application of the third

dimension. The categories for each facet are summa-

rized in Table 1 and described next.

3.2.1 Dimensionality

We differentiate between 2D, combined 2D and 3D,

and 3D software visualizations. For this study, the last

two categories are focused.

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Figure 1: Process model for hybrid approach: Mapping study (Petersen et al., 2008) and literature review (Brocke et al.,

2009).

3.2.2 Aspect

The different aspects of software that can be visual-

ized are based on (Diehl, 2007). He deﬁnes soft-

ware visualization as ”[...] the visualization of ar-

tifacts related to software and its development pro-

cess.”. These artifacts can contain information about

the structure, the behavior, or the evolution of the

software system. Structure includes program code,

data structures, the static call graph, relations, and the

organization of the software system. Behavior covers

its execution with real and abstract data. Evolution

refers to its development process.

Table 1: Classiﬁcation scheme for the study.

Facet Category

Dimensionality

2D and 3D

Aspect

Structure

Behavior

Evolution

Year 1991—2013

Evaluation

Anecdotal Case Study (Example)

Empirical

Case Study (User)

Controlled Experiment

Method

Questionnaire

Analytic

Guideline Checking

Heuristic Evaluation

Application

Extended 2D

Full 3D

2D layout org. in 3D

3D as time

Stacked views

3D for cognition

Local ﬁsh-eye

3.2.3 Year

The years for the relevant papers range from 1991 un-

til 2013. This period results from the search strategies

described in Section 3.3.

3.2.4 Evaluation Method

Typical evaluation methods in software visualization

are case study, controlled experiment, and question-

naire (Sjøberg et al., 2007; Seriai et al., 2014). How-

ever, the term case study is used in two different ways

in software visualization. On the one hand, a case

study is the demonstration of a working example as

in (Wettel and Lanza, 2008). This type of case study

is without representative users. On the other hand,

a case study actually involves representative users as

in (Denford et al., 2002). The second type also in-

cludes explorative user studies as in (Lanza et al.,

2013). Thus, we differentiate between case study (ex-

ample) and case study (user). In addition, we found

guideline checking and heuristic evaluation described

in (Andrews, 2008). All methods can further be clas-

siﬁed into anecdotal, empirical, and analytic evalua-

tion methods (Hundhausen, 1996; Hundhausen et al.,

2002). Anecdotal methods use compelling examples,

empirical methods involve representative users, and

analytic methods are performed by evaluation experts

using guidelines or heuristics.

3.2.5 Application of the Third Dimension

(Reiss, 1995) identiﬁed six different categories for the

application of the third dimension. As there were pa-

pers not ﬁtting in any of these categories, we intro-

duced another one resulting in the following seven

categories.

1. Extended 2D: A 2D layout is extended to 3D re-

sulting in an additional dimension. This dimen-

sion can be used to display further information,

such as software metrics as done in sv3D (Mar-

Past,Present,andFutureof3DSoftwareVisualization-ASystematicLiteratureAnalysis

cus et al., 2003) or CodeCity (Wettel and Lanza,

2007).

2. Local ﬁsh-eye: Another technique builds upon a

2D layout where the user is able to select a set of

nodes and place them at the front. This technique

uses perspective to make the selected nodes ap-

pear bigger and the other ones smaller. It results

in local ﬁsh-eye views without changing the orig-

inal graph such as in rubber sheet (Sarkar et al.,

1993).

3. 2D layout organized in 3D: The third technique

takes a 2D layout and the information is organized

in a 3D space, such as with cone and cam trees

(Robertson et al., 1991) or with hyperbolic trees

(Munzner, 1997). It is usually applied to get more

space and to minimize edge-crossings. Two other

examples for this category are the perspectivewall

(Mackinlay et al., 1991) and the ‘code on the wall’

metaphor (Jackson et al., 2002).

4. Full 3D: The next technique moves from 2D to 3D

space and uses the full capabilities of three dimen-

sions. Examples are Angle (Churcher and Tech,

2003), Metaballs (Rilling and Mudur, 2005), and

the 3D scatter plot in ComVis (Bohner et al.,

2007).

5. 3D as time: Further, the third dimension is used

to represent time, such as in VRCS (Koike and

Chu, 1998), Vizz3D (L¨owe and Panas, 2005), or

Palantr (Ripley et al., 2007).

6. Stacked views: This technique uses the third di-

mension to display several 2D views simultane-

ously. Examples are 3D sequence diagram as in

(Gil and Kent, 1998) and GEF3D (von Pilgrim

and Duske, 2008).

7. 3D for cognition: Finally, 3D shapes are applied

to support the mental model and to optimize the

cognition of the visualization. Examples for this

category are Geons (Irani and Ware, 2003) and the

use of social agents to visualize software scenar-

ios (Alspaugh et al., 2006).

3.3 Conduct Search

We combined three search methods in order to make

the sample more representative. First, we browsed

manually through all publications from relevant

workshops and conferences in the ﬁeld of software

visualization including SoftVis (2003, 2005, 2006,

2008, 2010), VisSoft (2002, 2003, 2005, 2007, 2009,

2011, 2013), IWPC/ICPC (1998-2013), Dagstuhl

Seminar on Software Visualization (2001), OOPSLA

Workshop on Software Visualization (2001), and

ICSE Workshop on Software Visualization (2001).

Second, we performed a keyword search on pub-

lications of relevant workshops and conferences in

the ﬁeld of information visualization including IEEE

VIS (2000-2013), PaciﬁcVis (2008-2013), and Euro-

Vis (2007-2013). The keyword was ”software visu-

alization”. Third, we conducted a backward search

using three state-of-the-art papers related to 3D soft-

ware visualization: (Graˇcanin et al., 2005), (Teyseyre

and Campo, 2009), and (Caserta and Zendra, 2011).

3.4 Screen & Classify Papers

The screening process for each paper included ti-

tle, abstract, conclusion, and—if necessary—further

parts. We used the following inclusion and exclusion

criteria to select the relevant papers. The publication

is included, if

• it deals with single 2D and 3D or 3D software vi-

sualizations (this automatically excludes surveys),

• it is peer reviewed including full papers, short

papers, and posters (this automatically excludes

books, book chapters, technical or research re-

ports, or white papers), and

• it is written in English

The publication is excluded, if

• the third dimension only serves aesthetic pur-

poses, i.e., augmented 2D visualizations (Stasko

and Wehrli, 1993), and

• it does not deal with software visualization, e.g.,

network visualization (hardware) or security.

In addition, we classiﬁed all relevant papers ac-

cording to the categories of the classiﬁcation scheme.

If the classiﬁcation of a paper was not unique, it was

marked, discussed by the authors, and ﬁnally included

and classiﬁed or excluded. For this reason, this step

has an iterative character. We used the reference man-

agement software Mendeley for screening and clas-

sifying the papers. The provided XML export was

helpful for further data processing.

3.5 Extract & Map Data

Major results of systematic mapping studies are fre-

quency/pie charts and bubble plots. Frequency/pie

charts show the distribution of a variable in an ab-

solute or relative manner. Bubble plots resemble x-

y scatter plots but with bubbles in category intersec-

tions where the size of a bubble represents frequencies

One paper was written in Italian, a language none of

the authors is ﬂuent in.

IVAPP2015-InternationalConferenceonInformationVisualizationTheoryandApplications

Table 2: Results for the three search strategies.

Manual Keyword Backw. Sum

Total 878 2998 510 4386

Dupl. 0 0 146 146

Other 405 2984 220 3609

2D 393 10 73 476

3D 80 4 71 155

of publications. We used Excel for data management

and the creation of the frequency/pie charts and bub-

ble plots or systematic maps respectively.

3.6 Analyze & Synthesize Papers

To get an overview of the application of the third di-

mension in software visualization, it was necessary

to conduct a more detailed analysis of the relevant

papers. This went beyond the screening process de-

scribed above. We had to study further parts of the

paper, especially sections explaining the concepts and

their implementation and the provided ﬁgures. The

results of this deeper review are also presented in a

systematic map.

3.7 Summarize Findings

Based on the results including frequency/pie charts

and the systematic maps, we deduced ﬁndings includ-

ing trends and research gaps in 3D software visual-

ization. Trends can be detected by analyzing the evo-

lution of the topic over time. Small bubbles in the

maps highlight research areas that might be under-

researched.

4 RESULTS

Table 2 shows the amount of papers identiﬁed with

each search strategy and Figure 2 details these results

with a Venn diagram.

Overall, 4386 papers were found, manually (878),

using a keyword search (2998), or using references

in surveys (510). From these, 146 papers were du-

plicates in the backward search which yields a total

of 4240 unique papers to be examined. From these,

631 papers deal with software visualization and 155

(24.6%) with 2D & 3D (41, 26.0%) or 3D only (114,

74.0%) software visualization. These were published

as full papers (116, 74.8%), short papers (17, 11.0%),

and posters (22, 14.2%). These 155 papers are the

input to the steps ‘extract & map data’ as well as ‘an-

alyze & synthesize papers’ and thus the basis for an-

swering the research questions.

Figure 2: Results for the three search strategies as a Venn

diagram.

4.1 RQ1: Which Workshops/

Conferences/ Journals Include

Papers on 3D Software

Visualization?

Figure 3 shows all workshops, conferences, and jour-

nals including papers with 3D software visualization

that were found using the method described in Sec-

tion 3.

We observed, that most of the 3D software visual-

ization papers were published on VisSoft (6 events, 30

papers before 2012) and SoftVis (5 events, 24 papers).

Figure 3: Workshops, conferences, and journals with 3D

software visualizations.

Past,Present,andFutureof3DSoftwareVisualization-ASystematicLiteratureAnalysis

After SoftVis and VisSoft merged in 2013, 6 papers

were published on the new VisSoft 2013. Further,

4 papers emerged from the precursor of SoftVis, the

Dagstuhl 2001 event. Altogether, 64 papers (41.29%)

containing 3D software visualization were published

on the main events.

An additional 15 papers were presented on

IWPC/ICPC (16 events). On the main visualization

conferences, a total of 9 papers are related to 3D

software visualization (InfoVis: 7, EuroVis: 1, Paci-

ﬁcVis: 0, related conferences/workshops: 1). For the

software engineering related conferences, the count

is 10 papers (ICSE: 5, WCRE: 4, SE: 1, OOPSLA:

1). Overall, these conferences contributed 34 papers

(21.94%) to our study. 40 other venues added 57 pa-

pers (36.77%), with at most 4 additional papers per

venue.

4.2 RQ2: Which Aspects of Software

Visualization (Structure, Behavior,

Evolution) are Visualized with 3D?

Figure 4 shows the distribution of the different aspects

displayed using 3D software visualization.

From the 155 papers analyzed, 67 (43.2%) visual-

ize structure alone, 54 (34.8%) structure and behavior,

18 (11.6%) structure and evolution, 6 (3.9%) structure

and behavior and evolution, 5 (3.2%) behavior alone,

and 5 (3.2%) evolution alone. That means, that 145

papers (93.5%) deal with structure alone or in com-

bination with behavior and/or evolution. No 3D visu-

alization was proposed for a combination of behavior

and evolution without the aspect of structure.

Figure 4: Aspect displayed using 3D software visualiza-

tions.

4.3 RQ3: How did 3D Software

Visualization evolve Over the Last

22 Years and what are Current

Trends?

Figures 5 and 6 show the evolution of 3D software vi-

sualizations from 1991 until 2013. Few papers were

found dealing explicitly with 3D software visualiza-

tion before 2001. Overall, 30 papers were published

between 1991 and 2000, between 1 and 6 papers per

year. All papers include structural aspects.

Between 2001 and 2008, 10 papers or more were

published each year on 3D software visualization,

with an exception of 2006, when only 6 papers ad-

dress this topic. Overall, from 2001 until 2008 two

thirds (67.7%) of the found papers were published.

Between 2009 and 2013, less papers were published

on this topic per year—between no papers in 2012

and eight papers in 2013. Overall, between 2001 and

2013, 126 papers dealing with 3D software visualiza-

tion were published. Most papers address structure

(56, 36.1%) or a combination of structure and behav-

ior (40, 25.8%), structure and evolution (13, 8.4%),

and structure, behavior, and evolution (6, 3.9%). Be-

havior alone (5, 3.2%) and evolution alone (5, 3.2%)

are rarely considered. It is remarkable, that the or-

der of the different aspects or combinations of aspects

regarding the amount of papers published stays the

same, independently of the year or the amount of pa-

pers published with only few exceptions: in 1994,

1995, and 1996 only papers combining structure and

behavior were published, structure and evolution (2)

is ranked ﬁrst in 1997 before structure alone (1) and

structure and behavior (1), structure and behavior (7)

is ranked ﬁrst in 2001 before structure alone, structure

and evolution (4) is ranked ﬁrst together with struc-

ture alone (4) in 2008 before structure and behavior

(3), and ﬁnally structure and behavior (3) is ranked

ﬁrst in 2013 before structure alone (2), structure, be-

havior, and evolution (2), and structure and evolution

(1). However, the amount of papers including 3D

software visualization is already small for each year.

4.4 RQ4: How is the Usefulness of the

proposed 3D Software

Visualizations Evaluated?

Figure 7 shows the different aspects of 3D software

visualization and their evaluation methods. Some 3D

software visualizations were evaluated using several

different evaluation methods. Therefore, the total

count is larger than the total number of papers ana-

lyzed.

IVAPP2015-InternationalConferenceonInformationVisualizationTheoryandApplications

Figure 5: Time vs. aspect for 3D software visualizations (1991-2000).

Figure 6: Time vs. aspect for 3D software visualizations (2001-2013).

The different aspects or combinations of aspects

were mostly evaluated using case studies showing

working examples (89, 53.3%) or not evaluated at

all (27, 16.2%). Some 3D visualizations were eval-

uated using case studies that involve representative

users (19, 11.4%). Few 3D visualizations were eval-

uated using controlled experiments (15, 9.0%). Other

evaluation methods used were guideline checking (10,

6.0%), questionnaires (7, 4.2%), and heuristic evalu-

ations (2, 1.2%).

With respect to the combination of aspect and

evaluation method, the bubble chart does not exhibit

any particularities. As most numbers are small, the

difference in ratios does not provide evidence for re-

lationships.

4.5 RQ5: How is the Third Dimension

Used?

Figure 8 shows the different aspects of 3D software

visualization and their application of the third dimen-

sion.

As a paper might contain multiple visualizations

or a visualization might belong to different categories

at the same time, the sum is larger than the number of

papers.

Most papers extended 2D visualizations (76,

39.4%), followed by full 3D (47, 24.4%), 2D layout

organized in 3D (31, 8.8%), 3D as time (17, 8.8%),

and stacked views (11, 5.7%). Another 11 papers

(5.7%) apply 3D for cognition only, while local ﬁsh-

Past,Present,andFutureof3DSoftwareVisualization-ASystematicLiteratureAnalysis

Figure 7: Evaluation methods vs. aspect for 3D software visualizations.

Figure 8: Application of the third dimension vs. aspect for 3D software visualizations.

eye is not applied at all. The latter two will not be

considered for the remaining analysis.

3D is applied for structure alone using extended

2D (30), full 3D (22), and 2D layout organized in 3D

(14). Further, extended 2D and full 3D are used for

all aspects and all combinations of aspects. 2D layout

organized in 3D is used for all aspects except struc-

ture and evolution. In contrast, 3D as time is mostly

used for structure and behavior (9), while only few

paper use it for structure and evolution (3), structure,

behavior, and evolution (2), behavior alone (2), and

evolution alone (1). Finally, stacked views are only

used for structure and behavior (8) and structure and

evolution (3). Neither 3D as time nor stacked views

are used for structure alone.

5 FINDINGS

Most papers dealing with 3D software visualization

were published on the major software visualization

conferences and workshops VisSoft (workshop until

2011), SoftVis (conference until 2010), and VisSoft

conference (since 2013). A substantial amount of pa-

IVAPP2015-InternationalConferenceonInformationVisualizationTheoryandApplications

Figure 9: Number of 2D & 3D or 3D publications over time.

pers was also published at IWPC/ICPC and InfoVis.

However, more than one third of the papers was pub-

lished on 45 different venues.

An important functional requirement of a soft-

ware visualization tool are multiple views (Kienle and

M¨uller, 2007). These multiple views provide a holis-

tic view of a software system combining structure,

behavior, and/or evolution and thus facilitate program

comprehension. The majority of 3D visualizations fo-

cus on structure, either alone (67, 43.2%) or in combi-

nation with behavior or evolution (72, 46.4%). Struc-

ture plays an important role in software visualization,

as one main objective is to give the formerly intangi-

ble and invisible phenomenon software a meaningful

shape (Graˇcanin et al., 2005). For the structural enti-

ties, such as namespaces/packages, classes, methods,

as well as attributes, and their relations suitable rep-

resentations are developed. The combination of these

representations form the basic shape of a visualiza-

tion that is usually enriched with behavioral or evo-

lutionary information. However, the combination of

all three aspects is rare in the analyzed 3D software

visualizations (6, 3.9%). One reason for this might be

the complexity such an approach requires. It is nec-

essary to combine structural information with a large

amount of data from execution traces and from ver-

sion control systems. This might be interpreted as a

serious deﬁcit of prototype implementations and as a

research gap as well.

The temporal analysis of the sample reveals that

researchers started in 1991 to scrutinize the visu-

alization of structure of software in 3D. One year

later, behavioral aspects, and six years later evolu-

tionary aspects, were also examined. Before 2001,

there was no 3D software visualization covering all

three aspects or behavior or evolution alone. In 2001,

the ﬁeld of software visualization started to establish

with ﬁrst tracks on software engineering conferences

and the Dagstuhl seminar. Since 2002, ﬁrst confer-

ences exclusively on software visualization have been

launched. These events have inﬂuenced the further

evolution of this area. For example, the ﬂuctuations

of the number of 3D publications depend on the dates

of the main conferences. In 2005, there was the high-

est number of publications (20) probably because Vis-

Soft and SoftVis took place at the same time. In 2012,

there was no publication and obviously none of these

two events took place. Additionally, it was found that

there was a trend to develop more 3D visualizations

between 2001 and 2008 (67.7% of the papers found)

with its peak around 2005 (Figure 9). The trend since

then has to be analyzed taking into account that the

3D survey of (Teyseyre and Campo, 2009) appeared

in 2009. Thus, only the main conferences or work-

shops contribute to the amount of 3D software sys-

tems while other venues are not represented. Fur-

ther, 2012 no event dedicated to software visualiza-

tion took place. Further analysis will show, if there is

a trend to continue developing 3D software visualiza-

tions.

Past,Present,andFutureof3DSoftwareVisualization-ASystematicLiteratureAnalysis

The applied evaluation methods are distributed

as follows: anecdotal (≈ 53%), empirical (≈ 24%),

and analytical (≈ 7%). Further, a large number of

visualizations does not have any evaluation at all

(≈ 16%). This is not surprising as no evaluation

at all means least effort, while anecdotal evidence

can be provided with some effort. Empirical stud-

ies, on the other hand, imply a large effort for plan-

ning, execution, and analysis. At the same time, the

target group—experienced software developers—are

not readily available for experiments. Finally, most

visualizations are already built taking guidelines into

account. Therefore, guideline checking will rarely

provide any beneﬁts. In summary, the formerly stated

need for more empirical evaluations of 3D software

visualizations by (Teyseyre and Campo, 2009) still

exists.

The most frequently used category for the applica-

tion of the third dimension is extending a 2D visual-

ization (76, 39.4%). The resulting additional dimen-

sion is used for example to represent software metrics,

such as LOC (Boccuzzo and Gall, 2007; Alam and

Dugerdil, 2007; Wettel and Lanza, 2007; Kuhn et al.,

2010), complexity (Sharif and Jetty, 2013; Balogh

and Beszedes, 2013), or the number of modiﬁcations

(Steinbr¨uckner and Lewerentz, 2010), for relations

(Balzer et al., 2004; Caserta et al., 2011), as well as

for instances (Greevy et al., 2005; Waller et al., 2013).

In some cases, the use of this dimension is conﬁg-

urable by the user (Marcus et al., 2003; L¨owe and

Panas, 2005).

In the next two categories—full 3D (47, 24.4%)

and 2D layout organized in 3D (31, 16.1%)—the ad-

vantage of 3D lies in the additional space that is avail-

able to represent solid 3D shapes or to optimize the

layout, e.g., to avoid edge-crossings in graphs. The

categories 3D as time (17, 8.8%) and stacked views

(11, 5.7%) are exclusively used in visualizations con-

taining behavioral and/or evolutionary information.

Hence, these two categories are suitable for represent-

ing dynamics.

Finally, 3D is used for cognition (11, 5.7%). (Irani

and Ware, 2003) compared 2D UML diagrams and

3D geon diagrams in several experiments. Theyfound

out that substructures can be identiﬁed more accu-

rately with shaded components than with 2D outline

equivalents and that they are remembered more reli-

ably. Here, the third dimension does not convey ad-

ditional information but it facilitates the perception of

the human visual system.

To sum it up, it could be helpful to start with a

basic 2D shape visualizing the structure of a software

system. Further, this basic shape is extended with be-

havioral and evolutionary aspects using one or a com-

bination of the identiﬁed applications of the third di-

mension. That is, a useful software visualization is

not necessarily limited to 3D. Rather, the optimal in-

terplay between 2D and 3D may be the clue to the

successful integration of all three aspects.

6 THREATS TO VALIDITY

6.1 Reliability

We have described our method in detail and men-

tioned all sources in order to make this study repeat-

able.

6.2 Objectivity

The researcher bias mainly inﬂuences the selection

and the classiﬁcation of papers.

6.2.1 Selection of Papers

We increased the representative quality of the study

by triangulating three different search methods. We

started with manual browsing of the proceedings of

the main software visualization events, continued

with a keyword search of important information visu-

alization conferences, and ﬁnished with a backward

search using state-of-the-art surveys in the ﬁeld of

software visualization.

6.2.2 Classiﬁcation of Papers

Each paper whose classiﬁcation was not clear, was

marked as ‘needs review’ and thoroughly discussed.

Overall, there were three iterations in the ‘screen &

classify’ step with altogether 60 discussable papers.

6.3 Internal and External Validity

We addressed the internal validity of our study by

starting with a top-down approach to built the clas-

siﬁcation scheme. Thus, we used an established base

for the categories. We have tried to increase the exter-

nal validity by increasing the representative level of

the sample as described in Section 6.2.1.

7 CONCLUSION

We performed a systematic literature analysis using a

hybrid approach that combined a systematic mapping

study followed by a systematic literature review. The

IVAPP2015-InternationalConferenceonInformationVisualizationTheoryandApplications

research questions addressed where papers about 3D

software visualization were published, which aspects

were visualized, how the topic evolved over the last

22 years, how the usefulness of the 3D software visu-

alizations was evaluated, and how the third dimension

was used.

The results show that the aspect ‘structure’, the

evaluation method ‘case study (example)’, and the ap-

plication of the third dimension ‘extended 2D’ are

dominant. The combination of ‘structure’ with ‘be-

havior’ or ‘evolution’ was also found relatively often.

Although, the combination of all three aspects in

one software visualization tool providing a holistic

view is complex and challenging to implement, we

see therein a research gap for the future.

The need for more empirical evaluations of 3D

software visualizations stated earlier still exists and

should be addressed in future work.

Finally, the third dimension is mainly used to rep-

resent software metrics. Other successful applications

are to use the additional space for solid 3D shapes and

for an optimized layout, to represent time, and to am-

plify cognition. Probably, the optimal interplay be-

tween 2D and 3D views plays an important role in the

future.

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