CSC 321.01, Class 05: Web technologies
- Notes and news
- Upcoming work
- Extra credit
- 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.
- 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)
- CS extras Thursday: Sam’s students
- Rebecca Wingo: How to Harvest History. Friday Feb. 2, 4pm, Burling
- Workshop: Saturday Feb. 3, 10-1, DLab
- Register for workshop at https://grinnell.formstack.com/forms/wingo_workshop
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.
- Breaking a larger message into smaller pieces (and rearrange)
- Providing feedback and error messages
- 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.
- 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
- 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.
- Specifies the kinds of requests
- 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)
- 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
- 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
- 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.
- State - Cookies. Browser sends information to client. Client should send it back to browser with the next request.
Technologies mentioned (or that I should have mentioned)
- HTTP Cookies
- CSS - Didn’t cover
- DNS - Didn’t cover