Internet Basics Dr. Norm Friesen June 22, 2007

Questions What is the Internet? What is the Web? How are they different? How do they work? How do they differ technically from other communications media (e.g. telephone)?

The Web for Absolute Beginners (1 of 2) The Web is a series of documents, joined together by links. These links (which can take the form underlined text, text labels or images) can be followed by simply being selected or clicked. These documents can originate from almost anywhere in the world. Hypertext - a term that significantly predates the Web, referring to a collection of documents (or "nodes") containing cross-references or "links" which, with the aid of an interactive browser program, allow the reader to move easily from one document to another.

The Web for Absolute Beginners (1 of 2) Hypermedia - The extension of hypertext to include other media - sound, graphics, and video - has been termed "hypermedia." Web documents - Unlike text documents, Web pages can be dynamic and interactive: their contents can change in response to the reader or user's actions. Most dynamic Websites ( use information stored in databases to provide textual, numeric and other types of content for these pages.

A Browser - A browser (Internet Explorer, Firefox or another system) is the software used to view and interact with Web documents. Client and Server - There are two basic categories of computers associated with the Web and the Internet. The client computer is used to view Web pages with a browser and an Internet connection of some kind. When you (or your students) access WebCT from home, office, a computer lab, or a classroom, you will be using a client computer.

The server computer stores Web documents and "serves" their contents across the Web. Server computers can be located anywhere in the world, but must be connected to the Web using a permanent, high-speed link. Software that makes Websites interactive and dynamic is generally located on the server. It generally involves a database. This means that for most types of Web-based interactivity, a standard Web browser is sufficient.

Protocol: specific rules for accessing and transmitting data. Different protocols (e.g. "http" or "shttp") are used for different kinds of information. (often includes errors) URL or Web Address: a combination of characters (letters, numbers, punctuation) that is unique on the Web, and that indicates the specific location of a file or resource on a particular server.

Addresses Flash & Java Applets are examples of technologies that provide interactivity by being downloaded to and operating on the client computer. Document Locations or Web Addresses Each page or document on the Web has a unique address. This address identifies every important element involved in accessing the document, including: –the protocol or set of technical rules used to transmit the document –the organization providing the server that hosts the document on the Web –the nature or nationality of the organization –the part of the server accessed (port number) –the computer directories or folders in which the Web page is stored (optional) –the name of the Web page file

"Layers" Computer and network systems are designed in terms of clearly separated but independent components. In a network, these are referred to as "layers" (can be divided in different ways): –Physical: the actual wire or fibre on which information is transmitted; can be phone line –Application: –Content:

Websites sub-site structure often contains the real "content" of the web site; often uses a nonhierarchical organizational logic linear: most common format; useful for documents listing or index (usually alphabetical): useful for links or alternative organization of larger sites grid: useful for large, uniform information sets, like an expanded table. Can be combined with a hierarchy. database: for searches on large information sets. Requires special server software.

Databases on the Web: An important example of Internet/PC Architecture To make the contents of a database accessible over the Web, it is necessary to make use of special software that resides on a server. Special software forms the middle component or tier in what is commonly known as a three-tier system. This simple "stack" architecture is comprised of: 1.Database Tier: the data or database file residing on the server. Also known as the database server. 2.Middle Tier: database connectivity software making the database securely available on the web. 3.Client Tier: the client or browser used to search and modify database records.

data is passed back and forth between these tiers or components, basically in the form of search requests and results. The middle tier acts as an interpreter, translating information into the different languages or protocols understood by the browser and database. –It receives a query from a web page form, coded in a web protocol. –It translates this query into a simple but powerful Structured Query Language (SQL) statement, which can be understood by almost any type of database. – the connectivity software receives the results from the database as pieces of text that it must then format as a web document using HTML (HyperText Markup Language).

TCP/IP Protocols The internet as a postal system, not a telephone system. Why?

Cold War and the Internet One central "hub" makes the entire network vulnerable Many "hubs" means that the network can operate even if one or more ceases to exist. DARPA: Defense Advanced Research Projects Agency