Analysis and Testing of Ajax-based Single-page Web Applications

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5.6.4 State Space The set of found states and generated HTML pages is by no means complete, i.e., Crawljax generates a static instance of the Ajax application but not necessarily the instance. This is partly inherent in dynamic web applications. Any crawler can only crawl and index a snapshot instance of a dynamic web application in a point of time. The number of possible states in the state space of almost any realistic web application is huge and can cause the well-know state explosion problem (Valmari, 1998). Just as a traditional web crawler, Crawljax provides the user with a set of configurable options to constrain the state space such as the maximum search depth level, the similarity threshold, maximum number of states per domain, maximum crawling time, and the option of ignoring external links and links that match some pre-defined set of regular expressions, e.g., mail:*, *.ps, *.pdf. The current implementation of Crawljax keeps the DOM states in the memory which can lead to an state explosion and out of memory exceptions with approximately 3000 states on a machine with a 1GB RAM. As an optimization step we intend to abstract and serialize the DOM state into a database and only keep a reference in the memory. This saves much space in the memory and enables us to handle much more states. With a cache mechanism, the essential states for analysis can be kept in the memory while the other ones can be retrieved from the database when needed in a later stage. 5.7 Applications As mentioned in the introduction, we believe that the crawling and generating capabilities of our approach have many applications for Ajax sites. 5.7.1 Search Engines We believe that the crawling techniques that are part of our solution can serve as a starting point and be adopted by general search engines to be able to crawl Ajax sites. General web search engines, such as Google and Yahoo!, cover only a portion of the web called the publicly indexable web which consists of the set of web pages reachable purely by following hypertext links, ignoring forms (Barbosa and Freire, 2007) and client-side scripting. The pages not reached this way are referred to as the hidden-web, which is estimated to comprise several millions of pages (Barbosa and Freire, 2007). With the wide adoption of Ajax techniques that we are witnessing today this figure will only increase. Although there has been extensive research on crawling and exposing the data behind forms (Barbosa and Freire, 2007; de Carvalho and Silva, 2004; Lage et al., 2004; Ntoulas et al., 2005; Raghavan and Garcia-Molina, 2001), crawling the hidden-web induced as a result of client-side scripting in general and Ajax in particular has gained very little attention so far. Consequently, while Ajax techniques are very promising in terms of improving 124 5.7. Applications
ich interactivity and responsiveness, Ajax sites themselves may very well be ignored by the search engines. 5.7.2 Discoverability There are some industrial proposed techniques that assist in making a modern Ajax website more accessible and discoverable by general search engines. Graceful Degradation In web engineering terms, the concept behind Graceful Degradation (Florins and Vanderdonckt, 2004) is to design and build for the latest and greatest useragent and then add support for less capable devices, i.e., focus on the majority on the mainstream and add some support for outsiders. Graceful Degradation allows a web site to ‘step down’ in such a way as to provide a reduced level of service rather than failing completely. A well-known example is the menu bar generated by JavaScript which would normally be totally ignored by search engines. By using HTML list items with hypertext links inside a noscript tag, the site can degrade gracefully. Progressive Enhancement The term Progressive Enhancement 19 has been used as the opposite side to Graceful Degradation. This technique aims for the lowest common denominator, i.e., a basic markup HTML document, and begins with a simple version of the web site, then adds enhancements and extra rich functionality for the more advanced user-agents using CSS and JavaScript. Server-side Generation Another way to expose the hidden-web content behind Ajax applications is by making the content available to search engines at the server-side by providing it in an accessible style. The content could, for instance, be exposed through RSS feeds. In the spirit of Progressive Enhancement, an approach called Hijax 20 involves building a traditional multi-page website first. Then, using unobtrusive event handlers, links and form submissions are intercepted and routed through the XMLHttpRequest object. Generating and serving both the Ajax and the multi-page version depending on the visiting user-agent is yet another approach. Another option is the use of XML/XSLT to generate indexable pages for search crawlers (Backbase, 2005). In these approaches, however, the server-side architecture will need to be quite modular, capable of returning delta changes as required by Ajax, as well as entire pages. 19 http://hesketh.com/publications/progressive enhancement paving way for future.html 20 http://www.domscripting.com/blog/display/41 Chapter 5. Crawling Ajax by Inferring User Interface State Changes 125
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Analysis and Testing of Ajax-based
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Contents Preface List of Acronyms i
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3.3.4 Single-page UI Model Definiti
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6.3.2 Trigger . . . . . . . . . . .
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Preface our years have passed since
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List of Acronyms ASP Active Server
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Introduction A ccording to recent s
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Figure 1.2 Screen shot of the Mosai
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Figure 1.4 Screen shot of OpenLaszl
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DOM APIs, a technique that was call
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Figure 1.6 Screen shot of Google Su
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Figure 1.7 Screen shot of Google Do
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Reengineering Analysis & Testing Ar
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client/server and network-based env
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To the best of our knowledge, at th
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Table 1.1 ❳❳ ❳ ❳ ❳❳ Cha
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equally and we chose to use an alph
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A Component- and Push-based Archite
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Page Internet Application aRchitect
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XML message containing directives t
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server sends the data to the client
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• Code reuse: shared implementati
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Rest provides Ajax demands Large-gr
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work well, will lose customers (Off
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communication between client and se
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GWT uses an RPC style of calling se
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DOM Client Browser event update Aja
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Client Server Legend Interaction po
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User Interactivity User-perceived L
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User Interactivity User-perceived L
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and does not comply with the Resour
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2.8.9 Design Models Figure 2.8 show
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of user tasks as first class entiti
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Migrating Multi-page Web Applicatio
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Web App 1 Page deltaChange viewChan
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gational and structural model of th
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Classic Web application Retrieve pa
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Algorithm 1 1: procedure start (Pag
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3.5.2 Identifying Elements The list
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Classification # of pages Home (Ind
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Figure 3.7 A candidate UI component
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target system. Even though the tech
Page 85 and 86: Third, we proposed a schema-based c
Page 87 and 88: Performance Testing of Data Deliver
Page 89 and 90: Figure 4.1 A screenshot taken from
Page 91 and 92: the user. Ideally, the pulling inte
Page 93 and 94: Streaming Figure 4.3 shows how the
Page 95 and 96: 4.4 Experimental Design In this sec
Page 97 and 98: Mean Publish Trip-time (MPT) We def
Page 99 and 100: tributes to the complexity of contr
Page 101 and 102: 8. Start the publisher and begin pu
Page 103 and 104: Figure 4.8 Sample Stock Ticker Appl
Page 105 and 106: Figure 4.9 Mean Publish Trip-time C
Page 107 and 108: 4.6.3 Received Publish Messages Fig
Page 109 and 110: Figure 4.12 Mean Number of Received
Page 111 and 112: Figure 4.13 Percentage of data item
Page 113 and 114: with pull is higher than push. This
Page 115 and 116: this scenario, a data item will onl
Page 117 and 118: With the pull approach, achieving t
Page 119 and 120: Crawling Ajax by Inferring User Int
Page 121 and 122: discusses the findings and open iss
Page 123 and 124: 5.3 A Method for Crawling Ajax The
Page 125 and 126: Robot click UI Browser generate cli
Page 127 and 128: 5.3.5 Creating States After firing
Page 129 and 130: 1 crawl MyAjaxSite { 2 url: http://
Page 131 and 132: The generator uses JTidy 10 to pret
Page 133 and 134: G1. For the experiment we have manu
Page 135: 19247 examined candidate elements,
Page 139 and 140: 5.8 Related Work The concept behind
Page 141 and 142: Invariant-Based Automatic Testing o
Page 143 and 144: has some support for client-side sc
Page 145 and 146: 6.3.2 Trigger Once we are able to d
Page 147 and 148: a new edge is created on the graph
Page 149 and 150: Other Invariants. In line with the
Page 151 and 152: 6.7.1 Oracle Comparators After each
Page 153 and 154: Algorithm 4 Pre/postCrawling hooks
Page 155 and 156: LOC Server-side LOC Client-side DOM
Page 157 and 158: todo items, removing all items inst
Page 159 and 160: Failure Cause Violated Invariant In
Page 161 and 162: plications) is that it is very hard
Page 163 and 164: 1. A series of fault models that ca
Page 165 and 166: Conclusion ith the advent of Ajax t
Page 167 and 168: out to be an appropriate framework
Page 169 and 170: plays a more prominent role in the
Page 171 and 172: correct behavior. Violations in the
Page 173 and 174: A great deal of our work has focuse
Page 175 and 176: A Single-page Ajax Example Applicat
Page 177 and 178: 1 if(navigator.appName == "Microsof
Page 179 and 180: Figure A.5 The run-time DOM instanc
Page 181 and 182: Figure A.7 The request/response tra
Page 183 and 184: Samenvatting ⋆ Analyse en Testing
Page 185 and 186: een dergelijk model te creëren, do
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Bibliography Abrams, M., Phanouriou
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Bouras, C. and Konidaris, A. (2005)
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De Lucia, A., Scanniello, G., and T
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Garofalakis, M., Gionis, A., Rastog
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Levenshtein, V. L. (1996). Binary c
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Netscape (1995). An exploration of
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Sprenkle, S., Pollock, L., Esquivel
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Wohlin, C., Runeson, P., Höst, M.,
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Curriculum Vitae Personal Data Full
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A. Dijkstra. Stepping through Haske
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M. A. Abam. New Data Structures and
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