Software Engineering for Internet Applications - Student Community

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eing among AOL's 28 million subscribers who share a common poolof proxy machines.Somehow you need to write some information out to an individualuser that will be returned on that user's next request.If all of your pages are generated by computer programs as opposedto being static HTML, one idea would be to rewrite all the hyperlinkson the pages served. Instead of sending the same files to everyone,with the same embedded URLs, customize the output so that a userwho follows a link is sending extra information back to the server.Here is an example:1. Visithttp://www.amazon.com/exec/obidos/ASIN/1588750019/.Note that 1588750019 is an International Standard BookNumber (ISBN) and completely identifies the product to bepresented.2. Look at your browser's Address field. You'll see somethinglike"http://www.amazon.com/exec/obidos/ASIN/1588750019/103-9609966-7089404". Amazon has redirected you to a pagethat includes a session ID (the stuff after the last slash)3. Roll your mouse over the hyperlinks on the page. Noticethat all the hyperlinks contain, at the end, this same sessionID.What if you put three books in your shopping cart? Amazon's servercould simply add three ISBNs to all the hyperlink URLs that youmight follow, separated by slashes. The URLs will be getting a bitlong but we can take encouragement from this quote from the HTTPspec:The HTTP protocol does not place any a priori limit on the length of aURI. Servers MUST be able to handle the URI of any resource theyserve, and SHOULD be able to handle URIs of unbounded length ifthey provide GET-based forms that could generate such URIs. Aserver SHOULD return 414 (Request-URI Too Long) status if a URIis longer than the server can handle (see section 10.4.15).We need not worry about turning away our best customers, the oneswith really big shopping carts, with a return status of "414 Request-URI Too Long". Or do we? Here is a comment from the HTTP spec:Note: Servers ought to be cautious about depending on URI lengthsabove 255 bytes, because some older client or proxyimplementations might not properly support these lengths.write clear English prose. Object Role Modeling (ORM), however, is ahigh-level formal specification language that looks promising forautomatic code generation in the coming years.A course for sophomoresLess mature engineers are going to have more difficulty choosing anappropriate set of tools, more difficulty with tool installation andadministration, and be less resourceful in seeking assistance whenappropriate. Thus if you are using this textbook with sophomores it isprobably a good idea to reduce flexibility and increase the physicalrootedness of the students and amount of hands-on assistanceavailable.Juniors and seniors might have had a summer jobs working withOracle and PHP on Debian Linux or with Microsoft .NET and SQLServer. They will probably be most productive if they can continueusing their familiar tools. Furthermore having a variety of tools in useduring the semester provides all the students with an opportunity tolearn a little bit about other development styles. The main risk tohaving students choose their tools is that some get sucked in bysoftware vendor hype and elect to use, for example, three-tieredarchitectures and application servers. At MIT the students have threeweeks before the start of the semester in which to install their chosentools. All of the MIT students who decided to go the applicationserver route were unable to get their systems up and running in timeto do the Basics problem set and hence were forced to drop theclass.For sophomores it is less likely that students will have extensivedevelopment experience with a particular set of tools and the risk of astudent choosing an inappropriate set of tools is increased. It may bebest to standardize on one set of tools so that everyone in the classis using the same systems.Universities spend hundreds of millions of dollars on dormitories sothat students can drink beer together but are seemingly reluctant tospend a dime on shared workspaces for students. This is a shamebecause for learning most technical material it is much more effectivefor students to work together and live separately. A student workingin a common laboratory with TAs and fellow students nearby won'tget stuck on something simple, such as "how do I launchSQL*Plus?". If you can possibly arrange a room with a bunch ofdesks and PCs and make that the center of your class, this will be anenormous help to less experienced students.14335
The one-term cram courseWhen teaching this material in one semester it is important thatstudents set up their environments before the first class meeting. Astudent might have to reinstall operating systems and relationaldatabase management systems, contact technical support, orabandon an initial choice of tools.The one-year thorough courseThere are several possible reasons for spreading this material over afull year:• students who don't appreciate or can't handle a gung-hopace• students working individually rather than in teams (morecoding per student)• opportunity to go deeper into some of the underlyingconcepts and systems• opportunity to launch services to real users mid-way throughthe courseIf we had an extra semester we would devote more attention to theinner workings of the relational database management system,demystifying the SQL parser and the various methods for handlingconcurrency. We would have the students look more carefully at theHTTP standard, possibly building their own simple Web server. Wewould cover some of the more exotic Web Consortium work, such assemantic Web and RDF and multi-modal interfaces. We woulddevote more time to performance measurement and engineering. Wewould push the teams and clients to launch their sites to real usersas quickly as possible so that the students could learn from useractivity and user feedback.It would be nice to include a section on high-level formal specificationof page flow and data model. Unfortunately as of 2003 there are notools available for this that compile into standard executablelanguages such as SQL and Java. A quick glance at UnifiedModeling Language (UML) might make one think that this is a usefulnod in the direction of formal specification of Internet applications.Unfortunately UML cannot be compiled into a working system norcan it be verified against a system built in executable languages suchas SQL and Java. Even if students mastered the 150 primitives ofUML, the only thing that they would learn is that people in the ITindustry can get paid high salaries despite never have learned to2.3 CookiesInstead of playing games with rewriting hyperlinks in HTML pages wecan take advantage of an extension to HTTP known as cookies. Wesaid that we needed a way to write some information out to anindividual user that will be returned on that user's next request. Thefirst paragraph ofhttp://home.netscape.com/newsref/std/cookie_spec.html readsCookies are a general mechanism which server side connections(such as CGI scripts) can use to both store and retrieve informationon the client side of the connection. The addition of a simple,persistent, client-side state significantly extends the capabilities ofWeb-based client/server applications.How does it work? After Joe Smith adds a book to his shopping cart,the server writesSet-Cookie: cart_contents=1588750019; path=/As long as Joe does not quit his browser, on every subsequentrequest to your server, the browser adds a header:Cookie: cart_contents=1588750019Your server-side scripts can read this header and extract the currentcontents of the shopping cart.Sound like the perfect solution? In some ways it is. If you're acomputer science egghead you can take pride in the fact that this is adistributed database management system. Instead of keeping a biglog file on your server, you're keeping bits of information onthousands of users' machines worldwide. But one problem withcookies is that the spec limits you to asking each browser to store nomore than 20 cookies on behalf of your server and each of thosecookies must be no more than 4 kilobytes in size. A minor problem isthat cookie information will be passed back up to your server onevery page load. If you have indeed indulged yourself by parking 80Kbytes of information in 20 cookies and your user is on a modem,this is going to slow down Web interaction.A deeper problem with cookies is that they aren't portable for theuser. If Joe Smith starts shopping from his desktop computer at workand wants to continue from a mobile phone in a taxi or from a Webbrowser at home, he can't retrieve the contents of his cart so far. Theshopping cart resides in the memory of his computer at work.33415
Page 1 and 2: SoftwareEngineering forInternetAppl
Page 3 and 4: Signature: ________________________
Page 5 and 6: end-users. We use every opportunity
Page 7 and 8: • availability of magnet content
Page 9 and 10: • we want to see if a student is
Page 11 and 12: you supply English-language queries
Page 13: What to do during lecturesWe try to
Page 17 and 18: 332• spend a term learning how to
Page 19 and 20: Once we've taught students how to b
Page 21 and 22: has permission to perform each task
Page 23 and 24: UDDIUnixcustomer's credit card. If
Page 25 and 26: thousands of concurrent users. This
Page 27 and 28: OraclePerlnamed XYZ" without the pr
Page 29 and 30: LDAPLinuxbits per color, a vastly s
Page 31 and 32: FilterFirewallFlat-fileGIF318functi
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Page 35 and 36: system. The authors of the core pro
Page 37 and 38: Sign-OffsTry to schedule comprehens
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Page 41 and 42: Client Tenure In Job (new, mid-term
Page 43 and 44: ReferencesEngagement ManagementSQL*
Page 45 and 46: Decision-makers often bring senior
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Page 49 and 50: 300always been written by programme
Page 51 and 52: 17.3 Professionalism in the Softwar
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Page 55 and 56: Chapter 17WriteupIf I am not for my
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15.18 Time and MotionThe team shoul
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select 227, 891, 'algorithm', curre
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create table km_object_views (objec
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• object-create• object-display
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The trees chapter of SQL for Web Ne
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);274-- ordering within a form, low
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and start the high-level document f
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Example Ontology 2: FlyingWe want a
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systems. What would a knowledge man
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spreadsheet". Other users can comme
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Chapter 15Metadata (and Automatic C
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{site url}{site description}en-usCo
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drawing on the intermodule API that
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At this point you have something of
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• description• URL for a photo
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Here's a raw SOAP request/response
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Chapter 14Distributed Computing wit
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conduct programmer job interviews h
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Most admin pages can be excluded fr
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content that should distinguish one
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Chapter 13Planning ReduxA lot has c
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the Internet-specific problem of no
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wouldn't see these dirty tricks unl
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12.8 Exercise 4: Big BrotherGeneral
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than one call to contains in the sa
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A third argument against the split
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way 1 1/16One might argue that this
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absquatulate 612bedizen 36, 9211cry
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What if the user typed multiple wor
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Chapter 12S E A R C HRecall from th
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long as it is much easier to remove
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features that are helpful? What fea
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made it in 1938)? Upon reflection,
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environment, we identify users by t
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those updates by no more than 1 min
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Balancer and mod_backhand, a load b
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translation had elapsed--the site w
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It seems reasonable to expect that
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11.1.5 Transport-Layer EncryptionWh
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such as ticket bookings would colla
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give their site a unique look and f
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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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