Software Engineering for Internet Applications - Student Community

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);96('submitted','rejected','approved','expired'))create view articles_approvedasselect *from articles_rawwhere editorial_status = 'approved';If you change your mind about how to represent approval status, youwon't need to update dozens of Web scripts; you need only changethe definition of the articles_approved view. (See the viewschapter of SQL for Web Nerds athttp://philip.greenspun.com/sql/views for more on this idea of usingSQL views as a means of programming abstraction.)6.2 Comments on ArticlesRecall the six required elements of online community:1. magnet content authored by experts2. means of collaboration3. powerful facilities for browsing and searching both magnetcontent and contributed content4. means of delegation of moderation5. means of identifying members who are imposing an undueburden on the community and ways of changing theirbehavior and/or excluding them from the community withoutthem realizing it6. means of software extension by community membersthemselvesA facility that lets a user post an alternative perspective to apublished article is a means of collaboration that distinguishes a onewaypublishing site from an online community. More interestingly, thefacility lifts the Internet application out of the constraints of the literateculture within which Western culture has operated ever sinceGutenberg (1452). A literate culture produces such works as theMichelin Green Guide to Italy: "Extending below the town is the parkof the 16th-century Villa Orsini (Parco dei Mostri) which is aMannerist creation with a series of fantastically shaped sculptures."If a friend of yours came back from this place and showed theseslides, you'd expect to hear something much richer and moreinteresting than the Michelin Guide's sentence. A literate cultureoperates with the implicit assumption that knowledge is closed, that3. Self-description: A machine-readable way for programs todescribe how they are supposed to be called, e.g., with WebServices Description Language (WSDL).4. Discovery: A way for programs to automatically learn aboutother programs, e.g., with Universal Description Discoveryand Integration (UDDI), standardized by www.uddi.org.We're currently moving from an environment where applications aredeployed on individual machines and Web servers, to a world whereapplications are composed of pieces -- called services in the currentjargon -- that are spread across many different machines, and wherethe services interact seamlessly and transparently to produce anoverall effect. While the consequences of this change could be minor,it's also possible that they could be as profound as the introduction ofthe Web. In any case, companies are introducing new Web serviceframeworks that exploit the new infrastructure. Microsoft's .NET isone such framework.In this chapter, you'll build applications that consume Web services tocombine data from from your online learning community with remotedata in Google and Amazon. You'll be building SOAP clients to thesepublic services. In the final exercises you'll be creating your ownservice that provides information about recent content appearing inyour community. You'll make this service available both in the de jurestandard of SOAP and the de facto standard of RSS, a breakout fromthe world of weblogs.**** insert figure *****Figure 1: A Web services interaction. Human users talk to servers Aand B via the HTTP protocol receiving results in HTML pages. WhenServer A needs to invoke a procedure on Server B it first tries tofigure out what the names of the functions are and their arguments.This information comes back in a Web Services DescriptionLanguage (WSDL) document. Using the information in that WSDLdocument, Server A is able to formulate a legal Simple ObjectAccess Protocol (SOAP) request and process the results.14.1 SOAP on the WireDepending on what tools you're using you might never need to knowwhat SOAP requests and replies actually look like. Nonetheless let'sstart with a behind-the-scenes look at SOAP messages, which aretypically sent across the network embedded in HTTP POSTs.253
Chapter 14Distributed Computing with HTTP, XML,SOAP, and WSDLItalian tourism can fit into a book. Perhaps the 350 pages of theGreen Guide aren't enough, but some quantity of writers and pageswould suffice to encapsulate everything worth knowing about Italy."I think there is a world market for maybe five computers." - ThomasWatson, chairman of IBM, 1943Perhaps Watson was off by four.In the early 90s, few people had heard of Tim Berners-Lee's WorldWide Web, and, of those that had, many fewer appreciated itssignificance. After all, computers had been connected to the Internetsince the 1970s, and transferring data among computers wascommonplace. Yet the Web brought something really new: theperspective of viewing the whole Internet as a single informationspace, where users accessing data could move seamlessly andtransparently from machine to machine by following links.A similar shift in perspective is currently underway, this time withapplication programs. Although distributed computing has beenaround for as long as there have been computer networks, it's onlyrecently that applications that draw upon many interconnectedmachines as one vast computing medium are being deployed on alarge scale. What's making this possible are new protocols fordistributed computing built upon HTTP, and that are designed forprograms interacting with programs, rather than for people surfingwith browsers.There are several kinds of protocols:1. Data exchange: Something better than scraping text fromWeb pages intended for humans to read. As you saw in theBasics chapter, you can use XML here.2. Program invocation: Some way to do remote methodinvocation, that is, for programs to call programs running onother machines and to reply to such invocations. Theemerging standard here, submitted to the Web Consortiumin May 2000, is called SOAP (Simple Object AccessProtocol).Oral cultures do not sharethis belief. Knowledge isopen-ended. People mayhold differing opinions withoutone person being wrong.There is not necessarily onetruth; there may be manytruths. Though he didn't growup in an oral culture,Shakespeare knew this.Watch Troilus and Cressidaand its five perspectives onthe nature of a woman's loveand try to figure out whichperspective Shakespearethinks is correct.Feminists, chauvinists,warmongers, pacifists, Jewhaters,inclusivists, cautiouspeople, heedless people,misers, doctors, medicalmalpractice lawyers, atheists,and the pious are all able toComments are often the mostinteresting material on a site. Here'sone fromhttp://philip.greenspun.com/humor/billgates:"I must say, that all of you who do notrecognize the absolute genius of BillGates are stupid. You say that bill gatesstole this operating system. Hmm.. ifind this interesting. If he stole it fromsteve jobs, why hasn't Mr. Jobsrelentlessly sued him and such.Because Mr. Jobs has no basis tosupport this. Macintosh operatesNOTHING like Windows 3.1 or Win95/NT/98. Now for the mac dissing.Mac's are good for 1 thing. Graphics.Thats all. Anything else a mac sucks at.You look in all the elementary schoolsof america.. You wont see a PC. Youllsee a mac. Why? Because Mac's areonly used by people with undevelopedbrains."-- Allen (chuggie@geocities.com),August 10, 1998quote Shakespeare in support of their beliefs. That's becauseShakespeare uses the multiple characters in each of his plays toshow his culture's multiple truths.In the 400 years since Shakespeare we've become much moreliterate. There is usually one dominant truth. Sometimes this isbecause we've truly figured something out. It is tough to argue that aphysics textbook on Newtonian mechanics should be an open-endeddiscussion (though a user comment facility might still be very usefulin providing clarifying explanations for confusing sections). Yet evenin the natural sciences, one can find many examples in which theculture of literacy distorts discourse.25297
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SoftwareEngineering forInternetAppl
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end-users. We use every opportunity
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• availability of magnet content
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• we want to see if a student is
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you supply English-language queries
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What to do during lecturesWe try to
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The one-term cram courseWhen teachi
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332• spend a term learning how to
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Once we've taught students how to b
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has permission to perform each task
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UDDIUnixcustomer's credit card. If
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thousands of concurrent users. This
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OraclePerlnamed XYZ" without the pr
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LDAPLinuxbits per color, a vastly s
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FilterFirewallFlat-fileGIF318functi
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when there is an educational dimens
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system. The authors of the core pro
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Sign-OffsTry to schedule comprehens
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scheduling goals that both you and
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Client Tenure In Job (new, mid-term
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ReferencesEngagement ManagementSQL*
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It isn't challenging to throw hardw
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Chapter 11Scaling GracefullyLet's l
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10.15 Beyond VoiceXML: Conversation
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Consider that if you're authenticat
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In this example, we:194• ask the
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As in any XML document, every openi
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(http://www.voicegenie.com). These
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Chapter 10Voice (VoiceXML)questions
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9.15 MoreStandards information:•
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9.14 The FutureIn most countries th
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9.10 Exercise 7: Build a Pulse Page
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9.6 Keypad HyperlinksLet's look at
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text/xml,application/xml,applicatio
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Protocol (IP) routing, a standard H
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