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Transcript of Announcements Due dates extended! Labs 2 and 3 due Monday 10pm Continuation of Networking postponed...
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Announcements
Due dates extended! Labs 2 and 3 due Monday 10pm
Continuation of Networking postponed until Monday
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Networking, URLs, and Pathnames
Internet and WWW
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Servers serve
Servers store and serve resources:Emails—gmail Files—dante and homerWeb pages—vergil and ovidPrintingDatabases—available to other computers
on the network
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Servers
One computer can serve many thingsWindows Vista have server software built in
to shareFiles, printers, over LAN
Other server software Windows Server 2008
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Servers
One computer serves many things—files, printing, email, and database…
One dedicated computer serves one thingOne computer serves filesOne computer serves Web pagesOne computer serves email
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Server
Servers fit into racks
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Servers
Empty rack
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Server farm
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Domain Name System
Translates domain name to ip addressEvery domain name has to be uniqueNetwork Solutions maintains the list
Private companyCentral database is the whois directory
Several dozen registrars work with Network Solutions to add names to the list
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DNS
Network Solutions tracks top-level domains
Any huge company with hundreds of thousands of IP addresses and host names wants to maintain its own domain name server for their domain.
Countries probably wants to administrate their top-level domain
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DNS
Solution: distributed databaseHuge companies own their own DNS servers
and they are in charge of maintaining themMicrosoft can change the database for its domain
whenever it wants to because it owns its domain name servers.
Every domain has a domain name server somewhere that handles its requests. A person maintains the records in that DNS.
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The DNS process
You click link, sending http request to Web browser for our course Web site.
Browser contacts its name server and says, "I need for you to convert a domain name to an IP address for me."
The name server may already know the IP address for our web site if another request to resolve it came in recently (name servers cache IP addresses to speed things up).
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DNS Process (continued)
If not cachedName server contacts first listed root name
servers. The root servers know the IP address for all of the name servers that handle the top-level domains. Your name server would ask the root for our courses.washington.edu name, and the root would say (assuming no caching), "I don't know the IP address for that, but here's the IP address for the EDU name server."
If unknown, it contacts the next root server
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Client/Server Interaction
For Web pages, the client requests a page, the server returns it• Two separate transmissions
Client
Server Client
ClientClient
Client
Client Client
Server
Client
ServerServer
Server
ServerServer
Server
request
reply
04/22/23D.A. Clements, MLIS, Information
SchoolServers serve many clients; clients visit many servers
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Internet
Internet is all the wires, routers, gateways, servers—all using TCP/IP to transfer packets
Many different protocols use the Internet ftp, smtp, chat, IM, Skype, VoIP, http
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World Wide Web
World Wide Web is the collection of servers & the Web pages they store and serve
Server—the Web site computerClient—the surfer’s browserwww—the traditional Web server name
Any name is OK Often multiple server names map to the same site:
MoMA.org and www.MoMA.org
04/22/23D.A. Clements, MLIS, Information
School
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HTTP
HyperText Transfer ProtocolUnderstands how to interpret URLs
Uniform Resource LocatorsDivides URL into server and pathname
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PROTOCOL
(Web)
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
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SERVERPROTOCOL
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
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SERVER
Read Right to Left
PROTOCOL
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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SERVER
1. Domain: edu
Read Right to Left
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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SERVER
2. Subdomain: washington
1. Domain: edu
Read Right to Left
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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SERVER
3. Server: faculty
2. Subdomain: washington
1. Domain: edu
Read Right to Left
http://faculty.washington.edu/daclem/fit100/sp09/index.html
HTTP
PROTOCOL
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PATHNAMESERVER
3. Server: faculty
2. Subdomain: washington
1. Domain: edu
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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PATHNAMESERVER
3. Server: faculty
2. Subdomain: washington
1. Domain: edu
Read Left to Right
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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PATHNAMESERVER
3. Server: faculty
2. Subdomain: washington
4. Account: daclem1. Domain: edu
Read Left to Right
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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PATHNAMESERVER
3. Server: faculty
5. Folder: fit100/sp092. Subdomain: washington
4. Account: daclem1. Domain: edu
Read Left to Right
HTTP
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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HTTP
PATHNAMESERVER
6. File: index.html3. Server: faculty
5. Folder: fit100/sp092. Subdomain: washington
4. Account: daclem1. Domain: edu
Read Left to Right
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
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HTTP
PATHNAMESERVER
6. File: index.html3. Server: faculty
5. Folder: fit100/sp092. Subdomain: washington
4. Account: daclem1. Domain: edu
Read Left to Right
http://faculty.washington.edu/daclem/fit100/sp09/index.html
PROTOCOL
Case SensitiveNot case sensitive
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HTML
•Validating • Paths for images and links
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Demonstration
After building a web page, we find it is wrong
Houston, we have a problem
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Debugging Demo
Intended page
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Paths
Two types of pathsRelative
To folder where this html page is locatedAbsolute
Complete URL
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Paths
Relative pathsrc="huskyTeam.jpg"
Absolute pathhref="
http://courses.washington.edu/fit100/au09/images/huskyTeam.jpg"
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Paths
Relative pathhref="huskyPride.html"
Absolute pathhref="
http://www.cs.washington.edu/education/courses/cse100/08sp/examples/huskyPride.html "
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http
http = HyperText Transfer Protocolhttps = Secure http
Starts every link and every Web addressSends pages across the Internet to Web
servers
04/22/23 D.A. Clements, MLIS, UW iSchool 36
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Hypertext links
A Web page is a collection of hypertext links, or linksLinks allow you to jump to another page
clear across the Web
04/22/23 D.A. Clements, MLIS, UW iSchool 37
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The Language of Web Pages
HTML = HyperText Markup LanguageThe language that Web browsers
understand
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HTML tags
The content with HTML tagging
<h1>My first Web page!</h1>
<p>A new paragraph…</p>
The Web page displayed in a Web browser
My first Web page!A new paragraph…
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HTML structures the content
Tags structure the pageFormerly, they also formatted the content;
now, that’s done by CSS
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Basic HTML page structure
All HTML files use the same structure:
<html> <head> <title> </title> </head> <body> </body></html>
D.A. Clements, MLIS, UW iSchool 4104/22/23
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Paired tags
Tags are paired—opening and closing tags
<html> <head> <title>Name of Page Goes Here </title> </head> <body> </body></html>
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Nested tags
Other tags "nest" inside the <html> tags:
<html> <head> <title>Name of Page Goes Here </title> </head> <body> </body></html>
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Basic HTML Structure
An HTML file is divided into head and body sections.
<html> <head> <title>Name of Page Goes Here </title> </head> <body> </body></html>
D.A. Clements, MLIS, UW iSchool 4404/22/23
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Basic HTML Structure
The <head> contains metadata.
<html> <head> <title>Name of Page Goes Here </title> Other header content goes here </head> <body> </body></html>
Metadata
D.A. Clements, MLIS, UW iSchool 4504/22/23
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The Header section
The head contains metadata.
<html> <head> <title>Name of Page Goes Here </title> Other metadata goes here </head> <body> </body></html>
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The Body section
The body contains the page content—everything that shows on the Web page.
<html> <head> <title>Name of Page Goes Here </title> </head> <body> Body content goes here </body></html>
Content
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Areas that are off limits
The body contains the page content—everything that shows on the Web page.
<html> <head> <title>Name of Page Goes Here </title> </head>
No content here <body> Body content goes here </body></html>
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Areas that are off limits
The body contains the page content—everything that shows on the Web page.
<html> <head> <title>Name of Page Goes Here </title> </head> <body> Body content goes here </body></html>
No content here
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HTML AND VALIDATION
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Nesting Rules—by tag
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Not Allowed Inside Other Tags May Nest Inside These Exceptions:
h1, h2, h3, h4, h5, h6ol, ul, dlhrtable
div, form, blockquote, li, td, th
Tags that Must Nest Inside Others Exceptions
brImgspana
None
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Nesting Rules—Specific Tags
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Inner Tag Specific Outer Tag
td or th tr
tr thead or tbody
thead or tbody table
li ol or ul
input, button, textarea, select form
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Valid code
Invalid code
Error Message:
Error Messages—Tag Order
<tag1><tag2>content</tag1></tag2>
<tag1><tag2>content</tag2></tag1>
Simile:
<FedEx><bubbleWrap>Present</bubbleWrap></FedEx>
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Nesting error: tag2 must be closed before closing tag1
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Valid code
Invalid code
Error Message:
<tag1><tag2>content</tag1></tag2>
<tag1><tag2>content</tag1></tag2>
<tag1>
<tag2>content</tag2>
</tag1>
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Nesting error: tag2 must be closed before closing tag1
Error Messages—Alternate Fix
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Tag Location Rules
All tagsMust be nested inside head or bodyCannot be outside head or body or htmlCannot be between head and body
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Valid code
Invalid code
Error Message:
Error Messages—Tag Location
<html>
<head></head>
<sometag>Neither tags nor content can go here</sometag>
<body></body>
</html>And the long page is done.
<html>
<head>Metadata tags must go here</head>
<body>Content tags must go here</body>
</html>
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The tag <sometag> is not allowed within: html
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Valid code
Invalid code
Error Message:
Error Messages—No DOCTYPE
<html>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
04/22/23 D.A. Clements, MLIS, UW iSchool 57
No DOCTYPE found!
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Error Messages—Image Tags
<img scr="kitten.jpg" >
<img src="kitten.jpg"
alt="young spokespurrrrson" />
04/22/23 D.A. Clements, MLIS, UW iSchool 58
There is no scr attribute for: img Missing alt tag Missing closing img tag
![Page 59: Announcements Due dates extended! Labs 2 and 3 due Monday 10pm Continuation of Networking postponed until Monday.](https://reader036.fdocuments.in/reader036/viewer/2022062809/5697bf9a1a28abf838c9236c/html5/thumbnails/59.jpg)
Other image problems
Kitten.jpg ≠ Kitten.JPG ≠ Kitten.pngPuppy.png ≠ Puppy.jpg.png
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![Page 60: Announcements Due dates extended! Labs 2 and 3 due Monday 10pm Continuation of Networking postponed until Monday.](https://reader036.fdocuments.in/reader036/viewer/2022062809/5697bf9a1a28abf838c9236c/html5/thumbnails/60.jpg)
Quiz topics
TCP/IP LAN, WAN, GUI HTTP HTML URL Dante White space Internet WWW Server