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Research studies on cloud computing:

a systematic literature review Gianmario Motta DIS – University of Pavia motta05@unipv.it

Nicola Sfondrini DIS – University of Pavia nicola.sfondrini01@ateneopv.it

Abstract We present a review on Cloud Computing through a systematic analysis of some 79 articles, published in first rank journals and conferences in 2008-2011. We identify topics, issues, research strategies in the literature. The paper is structured in two parts: the first one describes what Systematic Literature Review (SLR) is, and the second one illustrates the framework to evaluate and select research work.

Systematic Literature Review (SLR): model & method

SLR can be defined as “explicitly formulated, reproducible and up-to-date summary” (Egger, Smith and O’Rourke 2001) that includes and extends the statistical results of a meta-analysis methodology. As opposed to narrative reviews, it is based on a structured method that is explicitly specified.

Figure 1 - Review Methods - (Pai et al. 2004)

Our SLR includes: 1. Question formulation 2. Source selection and inclusion of primary studies 3. Quality assessment and data extraction. 4. Synthesis and summary of study result 5. Results interpretation

These five activities can be summarized into three steps as shown in Figure 2 (Biolchini et al. 2005).

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Figure 2 - Systematic Review Process – Biolchini at al. 2005

Question Formulation

Our objective is to identify initiatives, experiences and viewpoints on Cloud Computing. Our key question What cloud computing really is and what level of maturity has reached is refined into Research Questions (RQs):

RQ1: What aspects are common in definitions of Cloud Computing?

RQ2: What are the most discussed topics on this technology? From SLR we expect:

Overview on the "state of the art" of Cloud Computing

The identification of gaps in current research, solutions, trends and future research and suggestions to the community of researchers and practitioners

Recommendations about a best practice to cloud computing that arise from SLR. Papers are classified into the following classes (Yang and Tate 2009) (Sriram and Khajeh-Hosseini 2010) clusters (table 1 ).

PRIMARY DOMANIS SUB-DOMAINS CONTENTS

General Overview Introduction, Definition guidelines, definitions, introductions and general aspects.

Technological Issues Network, Storage technology and components, mechanisms and architectures

Service Level Management Performance, Security performance studies to refine workflow setting, load balancing and end-user security.

Business Issues Cost, Legal Issues the economic value for providers and users and legal issues as data protection and privacy.

Case studies / real world applications and scenarios

Other Papers that cover multiple domains e.g. literature reviews

Table 1 – Cloud issues classification framework

Source Selection

The SLR has been performed through English-based web search engines:

IEEE Computer Society (www.computer.org)

ISI Web of Knowledge (apps.isiknowledge.com)

ACM Digital Library (portal.acm.org)

Google Scholar (scholar.google.com)

Science direct (www.sciencedirect.com)

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The SCOPUS Database (info.scopus.com) The choice of using only sources in English reflects the small number of relevant documents in other languages. Those sources are appropriate since they contain the work published by journals, conferences and workshops of high impact research community. Other important sources were not explicitly

included since they were indexed by some of the mentioned sources such as Google Scholar and SCOPUS Database Finally, books were not considered, because they often deal many different concepts that may cover too many areas. We have tried several search strings. In particular, have been used the keyword “Cloud Computing”.

Studies Selection

This selection is performed by inclusion and exclusion criteria arising on the research question. In a first step selection criteria were interpreted liberally and exclusions were only made because of the title, abstract and introduction. We will consider only the following “study types”:

Case Study: an exhaustive investigation on a single individual, group, incident, community or enterprise;

Theoretical: a study that includes guidelines or introductions to a particular subject or, finally, theoretical consideration on the research issue;

Surveys: a study with a statistical treatment of collected data;

Simulation: a study that reports simulation methods and related results;

Position Paper: a study that presents an opinion about a specific issue;

Instrument Development: a study used to present a new methodology or a modeling language;

Literature Review: a study that collects information on a particular topic through the analysis of the scientific literature .

According to the methodology described, a three stage selection has been used:

In a first stage, the search string runs on selected sources. An initial set of studies is obtained by reading of the title, abstract and introduction. Studies that were un related to any aspect of the research question are not included.

In a second stage, exclusion criteria reflect this rules: short papers, non-English papers, non-International Conference papers, non-International Workshop papers.

In a third stage, selection is based on compliance of the contents to research questions. Eventually, 79 articles were classified and analyzed by year of publication, geographical area, research method and publication.

Results: a statistical analysis

Time distribution

There are no significant articles before 2008, because the term “Cloud Computing” was coined in 2006, and only at the end of 2007 researchers started to consider this topic. The articles considered in our research range of time from 2008 to first quarter 2011. Our selection criteria considers the number of citations received and the impact factor. The reduced amount of time between the publication of considered articles and our analysis, however, raises an issue on the real value of citations. For, articles published at the end of 2010 had few months for citations. To normalize results, we weight citations by dividing the number of publications of each year for the number of years available to be cited as shown in Table 2. The number of articles published in 2011 has not been considered because too recent.

Year # of Publication % Weighted # of Publication %

2008 18 23% 6 12%

2009 38 48% 19 40%

2010 21 27% 21 44%

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2011 2 2% 2 4%

Total 79 100% 100%

Table 2 - Annual counts of research publications

Figure 3 shows the distribution of articles by comparing the real and weighted values. The steady growth

of publications is apparent.

Figure 3 - Annual counts of research publications

Geographic distribution

The geographical classification highlights a predictable overwhelming America ( Table 3).

Continents # of Publications %

Europe 19 24%

America 48 61%

Africa 1 1%

Asia 6 8%

Oceania 5 6%

Total 79 100%

Table 3 - Counts of publications organized by continents Table 4 shows the dominance of U.S. in research with 94% of the articles and a marginal role of Canada.

American Country # of Publications %

USA 45 94%

Canada 3 6%

Total 48 100%

Table 4 - Counts of publications in America Europe has only a quarter of the selected articles while the ROW accounts 15%. UK (37%) and Germany (32%) provide the main contribution, followed by a surprising Netherlands with over 20%. Italy and Greece play a secondary role by contributing each one with the publication of one article for our analysis.

European Country # of Publications %

UK 7 37%

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Germany 6 32%

Italy 1 5%

Holland 4 21%

Greece 1 5%

Total 19 100%

Table 5 - Counts of publications in Europe

In Table 6 shows China scientific community, if we include Hong Kong, Taiwan and Mainland China, totals 3.

Asian Country # of Publications %

China 1 17≈%

Honk Kong 1 17≈%

Japan 2 33≈%

Iran 1 17≈%

Taiwan 1 17≈%

Total 6 100%

Table 6 - Counts of publications in Asia

Publications (publishing outlet)

Surprisingly, the majority of the primary papers come from journals (56%) and conferences proceedings (42%). White papers, though only 2, are published by Amazon and Sun Microsystems, and provide an important contributions to the study of Cloud Computing; Amazon has recorded over 30 quotations to date.

Outlets # of Publications %

Journals 44 56%

Conferences Proceeding 33 42%

White Papers 2 2%

Total 79 100%

Table 7 - Publication outlets distribution

Study Types Classification

Table 8 shows the bulk of the articles use simulation (25%) and theoretical study (29%). The high presence of two so different approaches reflects the large amount of introductory articles and the mainly experimental ground of research .

Study Types # of Publications %

Case Study 13 17%

Theoretical Study 23 29%

Survey 2 3%

Simulation 20 25%

Position Paper 13 16%

Instrument Development 3 4%

Literature Review 5 6%

Total 79 100%

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Table 8 - Study Types distribution

Topic-Oriented Classification

Table 9 shows that “General Issues” (28%) and “Service Level Management” (26%) are the most frequent topics, followed by “Business Issues” (20%) and “Technological Issues” (14%); only the 8% of articles propose cloud technologies for new applications.

Primary Domains # of Publications %

General Issues 22 28%

Technological Issues 11 14%

Service Level Management 21 26%

Business Issues 16 20%

Uses Cases 6 8%

Other (SLR) 3 4%

Total 79 100%

Table 9 – Primary domains distribution Introductory studies and studies on management of quality total about 50% of the articles.

Figure 4 - Primary domains distribution

On Table 10, we observe the shift of research focus from introductory , distributed in the first two years, to the performance and quality of service, that become a key research in 2010.

Years General Issues Service Level Management

2008 8 3

2009 9 6

2010 5 11

2011 0 1

Total 22 21

Figure 5 - Topics distribution comparison by years In Figure 6 we observe a growth of articles on SLM. In 2010, introductory articles drop about 54% while articles on security and performance increase of approximately 55%.

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Figure 6 - Topics distribution comparison by years

The articles have been further divided into two sub-domains for a deeper analysis as shown in Table 10.

General Issues Quantity

Introduction 15

Definition 7

Total 22

Technological Issues Quantity

Network 6

Storage 5

Total 11

SLM Quantity

Performance 12

Security 9

Total 21

Business Issues Quantity

Cost 10

Legal issues 6

Total 16

Table 10 – Sub-domains articles distribution "General Issues" mainly contain introductory articles (68%), while a smaller part (32%) focus on definition. Despite their lower proportion, definition articles reflect that cloud computing is still an undefined and somewhat vague concept. The domain "Technological Issues" shows a solid balance of the two sub-domains "Network" (55%) and “Storage” (45%). In fact, bandwidth and storage are still limit full actualization of cloud computing. The domain "SLM" shows a slight majority of articles on performance, that is of great interest to researchers; for, cloud performance is critical to ensure high levels of service and to exploit cloud potential. A substantial part are articles on security (43%) showing a series of new adoption problems. Finally, the domain "Business Issues", with the 62% of articles about cost and economics of cloud systems,. confirms a great interest on cost saving. An important part are legal issues (38%) raised by the peculiar architecture of Cloud Computing that, alike security issues, slows down mass adoption. Figure 7 is a graphical representation to show "on the fly" the distribution of articles on the topics considered.

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Figure 7 – Sub-domains distribution

2.5 Conclusions We have illustrated the current academic research landscape on cloud computing, and classified the most discussed topics and has highlighted relevant trends. According to our statistical analysis, the number of researches shall increase exponentially thanks also to the growing economic interest on this technology. In the analysis, we have found different definitions that still show conceptual uncertainty. On the other side, National Institute of Standards and Technology describes cloud computing by a set of specific features and delivery / deployment models. In the analysis we have found that almost all articles, even in different domains, have at least addressed technological issues related to the adoption of cloud systems. These issues are analyzed, in most cases, in the provider’s perspective, while the quality of the service from the end-user’s viewpoint is almost neglected, as it is witnessed by the sole of study on SLA by Patel, P., A. Ranabahu & A. Sheth. Relevant work on the effective use of PaaS, that might be a strategic element in the future competition of vendors, is still scarce. Also standards are lacking, such as unified APIs, and interoperability of diverse systems so far is not granted. The analysis of business impact looks in an early stage. For, the assessment of benefits is not yet mature. Also, critical ethical and legal issues are still to be solved and, therefore, may delay or prevent a mass adoption. In short, this paper has highlighted the directions of academic research However, vendors tend to tailor cloud characteristics on their offerings (Pastaki Rad et al. 2009). The analysis of this very different point of view is a target of a further research.

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Bibliography by topic

Primary Domains

Sub Domains Topics Authors

General Definition Definitions Wang et al. 2008, Mell and Grance 2009, Varia 2008, Chappell 2009, Carolan et al. 2009, Armbrust et al. 2009

Introduction Technology Evolution

Voas and Zhang 2009, Foster et al. 2008, Mei, Chan and Tse 2008

Characteristics Vaquero et al. 2008, Mell and Grance 2009, Wang et al. 2008, Armbrust et al. 2010

Delivery Models Erdogmus 2009, Wang et al. 2008, Hoefer and Karagiannis 2010, Zhang, Cheng and Boutaba 2010, Mell and Grance 2009, Lenk et al. 2009, Grossman 2009, Hoefer and Karagiannis 2010, Lenk et al. 2009, Youseff, Butrico and Da Silva 2008

Deployment Models

Mell and Grance 2009, Zhang et al. 2010

Primary Domain

Sub Domains Topics Authors

Technological Issues

Network Node Assignment Algorithm

Hou et al. 2009

Self-Adaptation Network

Streitberger and Eymann 2009, Pallickara, Ekanayake and Fox 2008

Optical Bandwidth Chun and Maniatis 2009

Multicast Services Matos et al. 2009

Storage Data-Intensive Flow

Llorà et al. 2008

Data-Parallel Computing

Gu and Grossman 2008, Grossman et al. 2009

SQL data mining Johnson 2009, Grossman and Gu 2008

Semantic Web Mika and Tummarello 2008

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Primary Domains

Sub Domains Topics Authors

Use Cases / Mobile Devices Chun and Maniatis 2009

Large-scale Testing Ganon and Zilbershtein 2009, Mathew and Spraetz 2009

Software Model Wilson 2009

E-science Stein 2010

Social Collaboration Delic and Riley 2009

Other Yang and Tate 2009, Sriram and Khajeh-Hosseini 2010, Timmermans et al. 2010

Primary Domain

Sub Domains Topics Authors

Service Level Management

Performance Computational Power

Hoffa et al. 2008, Hazelhurst 2008, Napper and Bientinesi 2009, Ostermann et al. 2010, Ekanayake and Fox 2010

Performance Provisioning

Calheiros et al. 2011, Yigitbasi et al. 2009, Woo and Lee 2009

Load balancing Dornemann, Juhnke and Freisleben 2009, Lagar-Cavilla et al. 2009, Ekanayake and Fox 2010 Singh, Korupolu and Mohapatra 2008

Service Level Agreement

Patel, Ranabahu and Sheth 2009

Security Identity Management

Srinivasamurthy and Liu 2010, Takabi, Joshi and Ahn 2010, Tsai et al. 2010, Okuhara, Shiozaki and Suzuki 2010,

Privacy and Data Protection

Takabi et al. 2010, Yu et al. 2010,

Wang et al. 2009, Wang et al. 2010, Zissis and Lekkas 2010

Policy Integration Takabi et al. 2010, Paquette, Jaeger and Wilson 2010

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