Computer Science Illuminated, Third Edition: Goin

Computer Science Illuminated, Third Edition

Lab #1

Using the World Wide Web

1.1 Navigation

Figure 1: A typical web browser showing a web site.

In this lab, we'll explore the ins and outs of navigating the world wide web, (www), a practice more commonly known as surfing the web.

For the most part, if you wish to surf the web, the computer you use must have two key characteristics:

the computer must be connected to the Internet;
the computer must have a program (or application) known as a browser installed for you to use.

There is really no way of looking at a computer and knowing if it is connected to the Internet. If you're working in your school's lab, however, you can safely assume that your computer has a connection since very few computers these days are not online. Some at-home computers use a modem to dial into the internet, while machines in your campus lab are probably connected to the internet via an Ethernet connection (a wire). Once you're connected to the web, you can open a web browser to access the internet.

A web browser displaying a web page looks something like the image shown in Figure 1.1. Browsers are generally free, and in many cases are already installed in new computers.

Near the top of the browser's window, there is a location area where you can enter web addresses (known as Uniform Resource Locators or URLs). In the web browser shown in Figure 1, we have entered the web address: http://www.vusports.com While that may seem like a lot to type, you can shorten it by just entering www.vusports.com since many browsers will recognize the use of a shortened URLs.

Lab Activity #1:

Use a web browser to perform the following activities:

Visit the CNN web site, CNN.com. List the headlines of 3 of their top stories which can be found on the front page of the site.
Visit the web site for the cable television station CNBC (www.cnbc.com). Use the site to obtain current stock quotes for the following stocks:

Microsoft (ticker symbol: MSFT)

General Electric (ticker symbol: GE)

Pfizer Inc. (ticker symbol: PFE)

The Dow Jones Industrial Average (ticker symbol: $INDU)

Visit the web site www.slashdot.org. Then perform the following:

List the title and summarize the first story on the site.

Name three other topics about which you can find information on Slashdot.

Use MapQuest (www.mapquest.com) to obtain driving directions from your location to Newport, Rhode Island.

1.2 Search Engines

As you may already know, some web sites exist to help you find information on the Internet. These sites are known as search engines, and their job is to locate other web sites, determine what information is stored on them, and provide an easy method for you to search the web. Some search engines include:

www.google.com
www.yahoo.com
www.ask.com
www.looksmart.com

These search engines allow you to enter a search string (text to locate on web sites). Some search engines display a list of web sites broken into categories. In the latter case, each category is divided into sub-categories, and each sub-category is further divided until you find a list of web sites that you can choose from.

Many search engines use a software program called robots or spiders to crawl the web looking for new web sites. For each web site that a crawler visits, it is likely to find links to other web sites. These links are then followed by the crawler and analyzed in turn. All of the information gathered from the crawler is stored in a large database which is then searched when you wish to know where something might be located on the web. Search engines will generally provide a text area (such as the one shown in Figure 1.2) where you can provide search criteria to find what you are looking for.

Figure 2: An example of a search engine criteria field

For example, if you were searching for computer science programs in England, you might enter the criteria: computer science England. However, to make your search more effective (and possibly to return a smaller number of results from the database), you might consider grouping your criteria together. In our example, the term 'computer science' might be best enclosed in quotes to provide an additional hint to the search engine that those two words should appear in that order. When using a search engine and attempting a query, be sure to refer to what rules the engine has for specifying advanced criteria. Not all search engines will have the same methodology!

Lab Activity #2:

Perform each of the following activities:

Open a web browser and navigate to Yahoo! (www.yahoo.com). Use the category feature of Yahoo! to locate a web site for your favorite hobby or music act.
Perform a search on Google (www.google.com) to locate a web page that shows the list of maps for the transit system (bus routes, train routes, subway routes) for Philadelphia, Pennsylvania.

Use any search engine you wish to determine which United States University has the banana slug as their college mascot.

Use any search engine you wish to determine the population of London, England.

1.3 The Browser and the Server

The World Wide Web uses the client-server model. A client makes a request for information. A server is a computer dedicated to providing (serving) specific information and processing requests in particular ways. There are several kinds of servers, depending on the kinds of information and requests that they handle. A server may, for example:

deliver web pages (a web server)
handle e-mail traffic (a mail server)
provide access to particular files and programs (a file server)

Sometimes one machine will fulfill multiple server roles, however, when a web site receives a lot of traffic (many requests are made for its pages), a comuter will be dedicated soley to serving its web pages. In cases of very high traffic, more than one machine will be used. For example, a web site like CNN.com has one or more computers that do nothing but serve web pages to anyone who asks for them.

To continue our discussion of web navigation, let's consider how web browsers work. A Web browser establishes a connection from your computer to a machine elsewhere on the Internet. This process is depicted in Figure 1.3, which is borrowed from Chapter 16 of the textbook.

Figure 3: The interaction between a browser and a Web server

When your browser asks a server for a Web page, a single request for the page is issued to the server. The sever will then respond with the page, (assuming the request was made correctly). After receiving the page, your browser will examine the page (before displaying it) to determine if additional requests may need to be made to the server. If the web page contains graphics or images, a request will be made for each graphic or image on the page.

A Web server is not only the computer that serves web pages, but also the specific server software used to process the requests. For example, Microsoft has it's own server software that you can use to set up a web server. The Apache server software is free of charge, developed by a set of cooperating programmers.

Lab Activity #3:

Use a web browser to visit the web site www.netcraft.com. Explore the Netcraft site and determine the following:

When was the more recent Web Server Survey performed and which web server software (listed as the Developer) was used the most to provide web pages on the Internet? What percent of web sites used this developer's server?
How many web sites did the most recent Web Server Survey receive a response from?
Use the "What's that site running?" feature to determine what server and operating system the following sites use to operate:

www.cnn.com
www.hotmail.com
www.space.com
www.cia.gov

1.4 Downloading

Let's say you are browsing a web site and see an image that you'd like to copy by downloading it on to your machine. Since your seeing the image, your web browser has actually already downloaded the image. The image however, is only saved in a temporary location (known as a cache) which is periodically erased so that other images and web pages can be obtained.

To download an image in order to keep it, right-click your mouse on the desired image and look for a menu item labeled Save Image As... Select that menu item, and provide a name and storage location for the image in the dialog window that appears. Click the OK or Save button and the image will be saved to your computer. Note that some images are copyrighted works (such as images from the Associated Press (AP), or other news services), so your use of these works may be very limited.

Once downloaded, you can include the image on another web page, in a word processing document, or use it as a screen background. In lab #4 we'll be working with images, and you will be building a web site about yourself. You might want to download your school's logo or another image to include on your web site.

Lab Activity #4:

Perform the following activities:

Download the image displayed at the right.

Use a web search engine to find a clip art web site where you can download free clip art. Specifically, look for clip art of people in a meeting.

Use the Google image search (images.google.com) to locate and download an image of famed computer scientist Edsger Dijkstra.

1.5 Viewing HTML Files

Most Web pages are nothing more than text files on a computer. In addition to the primary content of the page, these files contain human-readable codes (called tags) which describe how the web page should be formatted and displayed. For the most part, web browsers interpret these tags to determine how to display the information in the page. These tags are part of the Hypertext Markup Language (HTML).

This lab is the first of several that are designed to take you beyond the introduction to HTML that is provided in Chapter 16 of your textbook. In the remaining labs, we'll be walking you through the development of your own web site using HTML. We'll talk about each of the major tags, and how to use them, and provide you with examples and exercises to build your own web site.

As a preview, let's take a look at some HTML code. Most web browsers will not only display the web page for you, but allow you to actually see the underlying HTML code. That is, you can view the file that was transferred to your web browser, permitting you to see the entire document structure. To do this, first view any web page with your a web browser. Then, use your mouse to right-click on the web page (you can right-click anywhere on the page's text; try to stay away from links and images) and look for a menu item labeled View Page Source from the menu that appears. Click on that menu item and the web browser will display a window containing the HTML code for the current web page.

Viewing the underlying HTML code in this manner is often a useful technique. When you see a feature on a web page you like, you may be able to discover how it was done by viewing the underlying document.

Lab Activity #5:

View and print the source code for this web page. You may need to copy the source code to your system's clipboard and paste it into a simple text file editor application (such as the Windows notepad program) and then print the file.

About the labs:
These labs were developed in conjunction with the Jones and Bartlett textbook Computer Science Illuminated by Nell Dale and John Lewis.
ISBN: 0-7637-1760-6
Lab content developed by Pete DePasquale and John Lewis