Using the World Wide Web
For the most part, if you wish to surf the web, the computer you use must have two key characteristics:
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.
1.2 Search EnginesAs 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:
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.
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!
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:
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.
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.
1.4 DownloadingLet'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.
1.5 Viewing HTML FilesMost 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).
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.
About the labs:
These labs were developed in conjunction with the Jones and Bartlett textbook Computer Science Illuminated by Nell Dale and John Lewis.
Lab content developed by Pete DePasquale and John Lewis