Handout 15

Overview

The last assignment
Questions from Last Time
How the Web Works
Basic Tags
Examples
Putting your HTML on the Web
Searching the Web

How the Web Works

Your computer is the client.
You use a web browser to connect to a server.
When you connect to a server, you request specific content in the URL.
That content is typically a text document marked up with HTML: a web page.
The content is sent back to the client machine where the web browser renders it.
The web page can include additional URLs which you can follow to find more content...

Basic Tags

<html>: all HTML documents should begin and end with this tag.
<head>: the first item in an HTML document is the <head> which potentially contains a bunch of stuff we don't care about.
<title>: the one thing the <head> contains that we do care about is the title of the document set in between these tags.
<body>: after the head of the document comes the body, which contains most everything that is displayed on the web page. The body is set between these tags.
: this starts a new paragraph and does not need to be paired.
 : this starts a new line and is not paired.
<hr>: this draws a line across the screen and is not paired.
<h1-6>: headings are set with these tags; there are six levels.
: important text should be set in these.
: emphatic text should be set in these.
: if you want to directly set something in italics, use these.
: if you want to directly set something in boldface, use these.
<pre>: these mark text that is set in a monospaced font and set exactly as typed.
<center>: to center text.
<ol>: sets an ordered list; each item has a number.
<ul>: sets a bulleted list; each item has a bullet.
<li>: marks an individual item in either of those sorts of lists: does not have to be paired.
<a href="">: marks a hyperlink to another document or another place in the current document.
<a name="">: marks a location that can be hyperlinked to.
Entities. Since angled brackets are used to mark tags, if you want to type one of them directly, you need to use a special character. These character entities always begin with an ampersand (&) and end with a semicolon (;). We therefore need special character entities for left and right angled brackets and for ampersand:
- Left angled bracket (<): <
- Right angled bracket (>): >
- Ampersand (&): &

Examples

A basic frame (example)
Formatting (example)
Linking (example)

Putting your HTML on the web

Once you've created and tested your HTML file on your own computer, you need to put it on the mainframe. The easiest way to do this is with the SSH program. The file needs to be put in a directory that is visible to the web. This is typically called public_html, but may be called something else on some machines.
Editing your HTML remotely. You can do all your editing on your own computer, re-uploading the file each time. However, you may prefer to make minor modifications on the file directly on the remote host. There are several programs generally available on mainframe computers for editing your HTML. The easiest to use is pico and it is available on both syntax and the u-cluster.
Once you've got the file in the appropriate place on the remote machine, you should confirm that it is visible over the web. If I put an HTML file called myfile.html on the syntax machine, the URL is: http://syntax.sbs.arizona.edu/~hammond/myfile.html.
You may get an error when you try to access this file over the web. There are three possible kinds of errors. One possibility is that you get an error that indicates that the file isn't found. This usually means that you put it in the wrong place or entered the wrong URL. Another possibility is that the HTML code is wrong; this usually results in it simply displaying improperly in some way. A third possibility is that you may get a "permissions" error. This means that the file needs to be set to be readable by all. This can be fixed by executing this command on the remote machine. chmod a+r myfile.html.

Searching the web

This chapter includes a discussion of the LWP module and describes a program (websearch.pl) that uses it to search the web in an automated fashion. I won't cover this because of time constraints.