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CSC 321.01, Class 05: Web technologies


  • Preliminaries
    • Notes and news
    • Upcoming work
    • Extra credit
    • Questions
  • A broad overview of Web and related technologies
  • Three-tier architecture
  • Some notes on cookies



  • Fruit snax!
  • Classroom? Here or 3813?
  • Apologies for being behind in grading. I have a busy next few days, but I will do my best to catch up over the weekend.
  • Last reminder: If you have TuTh afternoons available for the next few weeks, you should consider Megan Goering ‘08’s “Design Thinking” course. TuTh 2:00-3:50, JRC 209. starting tomorrow.
  • Many of you received comments that you should be more thorough on your journal answers. Here’s an appropriate length one for part 1 of t he latest journal: DNS (Domain Name System) – The Domain Name System matches hostnames to IP addresses so that a browser user does not have to remember the IP addresses of each site they want to visit. The browser asks a DNS server where a given hostname is, and then receives an IP address that refers to the same place..
  • Mentor session 6-7:30pm tomorrow.

Upcoming work

  • Hartl 1 due Thursday at 10:30pm.
    • This should be less time-consuming than the Ruby exercises.
  • Hartl 2 due Sunday at 10:30pm.
    • This should take about the same amount of time as the first Hartl assignment.

Good things to do (Academic/Artistic)

Good things to do (Other)

  • WinC 6pm on Thursday. (Every other week.)
  • Posse Plus Retreat Reflections, Community Hour next week (Tuesday, 11am, JRC 101)


What topics did people want to hear about?
Here’s the approximate list I recorded.
  • HTML: 3
  • Three-tier model: 2
  • Broad overview: 2
  • Security: 2
  • Networks and network protocols: 2
  • Cookies: 2
  • Push vs. pull: 1
  • Stateless: 1
  • XML: 1
  • Alternatives to Rails: Python+Django, Node.js, PHP, …: 1
  • WEBrick and comparison to other servers: 1
  • Horizontal scaling: 1
  • MVC: 1
What’s with this “check” garbage? What does it mean in terms of my letter grades?
Check means “satisfactory”. If everything is satisfactory, you get a B.
Applies to reading journals only. “Satisfactory” on homework is an A-.
How do you timebox?
I spent N hours. This is what I achieved.
So you should probably stop at N hours minus 20 minutes to give yourself time to write something.
About three hours per Hartl assignment.

A broad overview of Web technologies

  • TCP/IP - How do you get information from computer to computer on a network of computers.
    • Routing
    • Breaking a larger message into smaller pieces (and rearrange)
    • Providing feedback and error messages
    • Etc.
    • Byte order (yay endian wars)
  • TCP/IP was designed so that you can layer other protocols on top of it. Dozens (if not more) for particular applications/situations/types of data. HTTP, FTP, Gopher, smtp, etc.
  • Early 1990’s TBL develops WWW.
    • HTTP
  • HTTP
    • Specifies the kinds of requests
      • GET a resource
      • POST a resource or request (typically interpreted as “here’s a request plus additional information”)
      • UPDATE a resource (rarely used)
      • DELETE a resource
      • Each Web application can have its own general semantics for what to do for each request.
    • Specifies the forms of responses
      • Numeric code (success or failure)
      • 404 - Not found
      • If it succeeds, type of data and content
    • “Stateless”
      • A stateful protocol remembers the state of the communication (e.g., where you are in a directory structure, what you’ve said recently, that you’ve authorized)
      • Stateless protocols don’t remember state (except for some tricks)
      • Assumption: If you call the same operations on the same values (that is, ask for the same URL), you get the same response.
  • Problem: How do I refer to information? URL.
    • Originally designed just for Web, but now expanded.
    • Protocol: http, https, ftp, gopher, mailto, file, …
    • Machine (or related info):
    • User information (and authentication)
    • Resource
    • Additional info
    • “Parameters” with a question mark and more info
    • Combination of “what I tell my Web browser” and “what my Web browser tells the server”
  • Problem: What do data look like? HTML
    • Information plus meta-information
    • Surround information with “tags” like <p>...</p>
  • It turns out that this isn’t as much as we’d like for many “applications” of the Web.
    • State - Cookies. Browser sends information to client. Client should send it back to browser with the next request.
      • Loses purity of reference of URLs
      • Raises security risks
    • Interactivity: We need programs to run on the page.
      • Java - Embedded application that should not talk to the rest of the page.
      • Flash - Embedded application that might be able to talk to the rest of the page and is written by people who don’t understand security.
      • JavaScript - Embedded code that is expected to interact with the page. (Good security model? We hope.)

Technologies mentioned (or that I should have mentioned)

  • TCP/IP
  • HTTP
  • HTTP Cookies
  • HTML
  • URI
  • JavaScript
  • CSS - Didn’t cover
  • DNS - Didn’t cover