Dear vergita,
Thanks for your question. First, let me request that if any of the
following is unclear or if you require any further research – please
don’t hesitate to ask me for a clarification.
Q1. Difference between Internet and WWW
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The Internet is a global system of interconnected networks, a “network
of networks.” Through the joint use of two protocols, TCP
(Transmission Control Protocol) and IP (Internet Protocol), any two
computers on any networks connected through the Internet can
communicate with each other and access data on each other’s storage
devices. The genesis of the idea for the Internet can be traced back
to 1959, when the Russians launched the Sputnik into orbit and the US
government decided it needs to build a dispersed communications
network that is not centrally controlled – to avoid the possibility of
the Russians taking out the entire American communications network
with one satellite-guided missile. The physical manifestation would
wait a decade – the kernel for today’s Internet was ARPANET, launched
in 1969.
The World Wide Web, or WWW for short, is the part of the Internet
accessible through HTTP or Hypertext Transfer Protocol using a browser
such as Internet Explorer (Microsoft) or Netscape Navigator. The
father of the Web is considered to be Tim Berners Lee, a researcher
based at CERN in Switzerland, who invented HTTP in 1991. This is
therefore the date typically used as the “birthday” of the Web.
The Internet includes far more information than is accessible through
the Web – for example, email is accessible through applications using
SMTP; newsgroups are accessible through NNTP; and files are accessible
through FTP.
Great Internet architecture diagram –
http://static.howstuffworks.com/gif/internet-infrastructure1.gif
Also, great article on how the Internet “works” –
http://computer.howstuffworks.com/internet-infrastructure.htm
A good Web diagram explaining how a browser and server interact is at
–
http://static.howstuffworks.com/gif/webserver-basic-sm.gif
A more complex diagram of Web architecture is at –
http://www.aspalliance.com/Yusuf/Article08/Architecture.gif
Q2. Definitions of Some WWW Related Terms
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a) HTTP – HyperText Transfer Protocol – A protocol is a standard set
of rules, typically put together by an international standards
organization. HTTP is the protocol that governs the rules for
accessing and displaying files on the WWW – it also enables the
concept of hypertext linking, which in turn allows us as users to
“surf the Web”. If TCP/IP are considered to be infrastructure
protocols, HTTP is an application-level protocol.
b) FTP – File Transfer Protocol – defines rules for the transfer of
files of any type between two computers interconnected through the
Internet. It is an application level protocol that runs on top of
TCP/IP.
c) URL – Uniform Resource Locator – specifies the location of a file
on the Internet. It includes several components – the protocol used
to access the file, e.g. http; the domain for the server on which the
file is resident, e.g. www.yahoo.com; the directory location on that
server, e.g. “images/landscapes/” – and the name of the file e.g.
usmap.gif. The entire URL would then look as follows –
http://www.yahoo.com/images/landscapes/usmap.gif
d) Proxy Server – a proxy server is a server positioned as a
gatekeeper of sorts between the Internet and a private network such as
a company or school’s internal network. The proxy server translates
requests for files coming either from the Internet or from the
internal network – if the request is from the Internet, the proxy
server locates the file and returns it to the requesting client; if
the request is from the internal network the proxy server will check
if the file requested is already resident in its memory (cache) – if
it is, it will immediately return this file to the internal client
requesting it; if it is not, it will request the file from the
Internet and return it to the requesting client once the file is
returned.
Q3. Cascading Style Sheets
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Cascading Style Sheets, also known as CSS, provide Web page creators
more control over the appearance of a Web page by creating a local
standard that determines the precedence of various Web page style
components when the page is displayed in a browser window. Such
components include backgrounds, fonts, colors etc.
While using individual HTML tags such as <font> and <background> allow
acute control over specific pages, by using CSS and applying it to an
entire site a consistency is achieved that lends the pages a more
professional look. Further, making a change to the entire set only
entails making a change to the CSS, and this in turn produces far more
manageable Web pages and a far more efficient Web page maintenance
process.
A “style” is simply a rule that instructs the browser how to display a
specific HTML tag – every tag has several properties associated with
it (e.g. <font> has color, size, type), and the “style” can provide
instructions for one or more of those tags. The “style sheet” is an
html file that specifies such rules for a variety of HTML tags that
are to be used in a set of Web pages.
Q4. Image Maps
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An image map is a graphic that has been organized in a way that allows
the user to click on various parts of it in order to initiate
different actions – most commonly, a link to another part of the page
or to another page altogether. Image maps can provide great
navigational aids – they are especially popular with geographic
applications, allowing users to focus in on a specific region by
clicking on smaller and smaller regions. They can also provide a more
intuitive view of the structure of a Web site, or of an organizational
hierarchy (imaging that each department on an organizational hierarchy
tree is clickable and leads to a diagram of that specific department’s
hierarchy, for example).
A client-side image map runs locally, on the user’s local machine, and
will therefore typically run quicker because the page will send fewer
queries to the server. They are also more versatile, allowing for
example the triggering and coordination of JavaScript events that can
further enhance the user’s experience.
Server-side image maps, however, are more popular, and are more widely
supported by browser applications. Server-side image maps depend on
the server to interpret the users actions on the image map – each such
action initiates a query that is returned to the server, which
interprets the action and send back the correct HTML file. Such image
maps are slower and less versatile in terms of the types of actions
that can be taken by users.
Q5. Types of Internet Connections
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The most popular types of Internet connections are dial-up, broadband
and wireless.
Dial-up Internet connections are still the most common, accounting for
upwards of 80% of connections in the US, for example. A dial-up
connection to the Internet can be established from any phone anywhere
in the world by connecting the phone line to a modem, and the modem to
the computer. The speed of such connections ranges from 14 Kbps
(Kilobits per second, a measure of bandwidth) to a maximum of 56 Kbps.
Typically speeds of 56 Kbps are not achieved, because of constraints
in the actual phone system. This speed is slow and generally
inadequate for anything involving more than basic Web pages with
minimal images.
Broadband Internet connections – there are actually several types of
broadband connections – cable Internet, delivered over standard cable
lines (the same ones that bring you cable TV); DSL, delivered over
phone lines; and ISDN or dedicated connections, delivered over
dedicated Internet lines. All of these provide connections that are
of adequate speed to view Web pages in all their glory, with complex
images, audio and even video. Cable Internet ranges in speed from 128
Kbps to 500 Kbps upload, and is typically 1 Mbps on the download end –
this means that you can view pages much faster than you can return
data; given these high speeds, the differences are negligible for
typical applications such as email but considerable if you’re trying
to video conference. DSL (Digital Subscriber Line) speed depends on
the distance from the nearest repeater and can range from 384 Kbps to
upwards of 1 Mbps. ISDN (Integrated Services Digital Network) is more
reliable since a digital connection is less sensitive to errors in
transmission (less noise) – and more flexible, since eight different
devices can be connected simultaneously (vs. one with cable and two
with DSL). ISDN speed is 128 Kbps. Broadband Internet can also be
set up as a dedicated line that connects directly to a NAP (Network
Access Point) – such connections can be extremely fast but also
extremely expensive.
Wireless Internet – there are two types of wireless Internet.
Satellite broadband provides 400 Kbps download and 128 Kbps upload
speed and is available anywhere, which is a huge advantage – but it’s
slower than cable and it costs more. The second type of wireless
Internet is extremely fast but effective only locally, and as such is
more relevant for intranets within homes and offices that are already
connected to the Internet via some other connection method. This kind
of connection is called a Wi-Fi connection, and it leverages the
802.11b wireless connectivity standard established by the IEEE.
Speeds can range up to 11 Mbps over several hundred feet – much faster
than any other method and much more effective for intra-office
communications.
Q6. Search Engines
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The most common method users leverage to locate Web sites of interest
is by use of a search engine. It is therefore extremely important to
ensure that one’s site is listed with all major search engines
individuals are likely to use.
A typical search engine is comprised of three components. First,
applications called ‘spiders’ or ‘crawlers’ which traverse the Web and
return information to a centralized server. Second, a program on that
centralized server that creates a catalog or index from the
information returned by the Web crawlers. And, third, an application
that is accessible through a browser that receives users’ requests,
searches its catalog and returns relevant results or ‘hits’ to the
users.
Web page creators can facilitate the work of spiders and the
effectiveness of search engines by constructing relevant headers and
Meta tags. Headers are fields that precede the main content of a file
and include a title and a brief description of the information in the
file. If a Web page includes a header it will typically be displayed
by the search engine – if it does not the search engine can use
various criteria to create a header but such a header will often be
less readable and less relevant.
Meta tags are HTML tags that can be used to describe in more detail
the contents of a Web page. Meta tags may include keywords and a
description defined by the Web page’s creator. Search engines seek
out both headers and Meta tags in order to optimize the results that
they return to users seeking pages.
Web pages can also be registered directly with search engines through
submission forms which most search engines make available somewhere on
their site. Some search engines now offer paid submission options
that can improve the placement of a site in the results list returned
to a searcher. Some companies provide services that allow multiple
submissions to dozens and even hundreds of Web sites.
Q7. Publishing Web Pages on the Web
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Basically, publishing a Web page means that the page has been placed
on a server that is connected to the Internet, in a directory that has
been designated as being “public” and is therefore accessible to other
Web users. FTP, or File Transfer Protocol, described above, is most
commonly used to upload pages to a server.
FTP can be used through a simple command line interface using DOS, or
it can be leveraged through a variety of applications that include
graphical user interfaces such as CuteFTP. FTP also allows for the
management of files and directories on Web servers, facilitating such
actions as file and directory renaming, deletion, movement and
creation.
In order to upload a Web page to a Web server using an FTP client one
would have to work through the following steps:
1) Create an HTML file, debug it and test it locally to ensure that it
is producing the results as planned
2) Name the file and save it locally
3) Run an ftp client locally
4) Log on to the remote server
5) Select the file
6) Upload the file to the relevant directory on the remote Web server
Q8. Critical Appraisal of Client and Server Side Scripting
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Scripting allows Web page creators to provide Web users with far more
dynamic Web pages than HTML could provide on its own, since HTML is by
definition a static markup language. There are two types of scripting
– server-side scripting, driven and interpreted by the server; and
client-side scripting, which can run on a user’s local machine
provided that the requisite software and applications are installed on
that machine apriori.
Server-side Scripting
**********************
Server-side scripting is programmed using CGI – Common Gateway
Interface. Such server-side scripting using CGI allows for a lot of
flexibility on the Web. CGI programs can be written using a variety of
Common (hence CGI – Common…) programming languages such as C, Java,
Pascal, C++ and Visual Basic. Such programs can also run on a variety
of different systems using many different kinds of O/S such as
Windows, UNIX, Amiga and any other operating system that is capable of
running a Web server. Platform agnostic programming languages such as
Perl allow one to write CGI programs that can be run on a variety of
platforms running any operating system.
CGI’s flexibility is further enhanced by its ability to serve as a
Gateway between human surfers and the universe of computers and
programs accessible over the Web, allowing, for example, a user
speaking and writing in English to interact with a database that
“speaks” SQL via forms interpreted by CGI.
Some of the other applications that can be enabled using CGI include
form-driven applications, bulletin board systems, chat, shopping carts
and Web stores, and database-driven applications such as contact
managers and calendars.
Server-side scripting can also be accomplished using other
technologies such as Netscape’s Live Wire and JavaScript. CGI does
offer far more flexibility because it is not browser-dependent – it is
therefore far more portable. So, CGI is highly flexible and
versatile, offering the ability to leverage a great deal of
functionality, but it is relatively slow because it is driven by
server-side response times, and it especially hampers speed of
execution when users are accessing the Internet using dial-up
connections (as most people are). Running on the server-side also
hampers scalability as a large number of simultaneous users can slow
response time to a virtual crawl.
Client-side Scripting
**********************
Client side scripting places the demand for processing power on the
client’s computer, and is therefore far more scalable. Most of what
can be accomplished by server-side CGI can also be accomplished by
client-side CGI – the server only has to be called upon if there is a
need to send or receive email, or to access remote files. Client-side
processing also increase security because most of the action happens
locally without calling on external factors.
Client-side scripting is typically written either in JavaScript or in
VBScript – a scripting language developed by Microsoft that is based
on its popular visual basic programming platform. Client-side
scripting offers less portability than server-side scripting does
because the browser must be capable of interpreting the scripting
language locally. It is more commonly used in well-controlled
environments such as on intranets where an IS department can guarantee
that all users machines are capable of running the scripts made
available to them. Client-side scripting can also be written in a
platform-agnostic manner using Java, but Java is extremely slow, even
when processed locally.
____________________________________________________
I hope this response adequately addresses your request. Please let me
know if you are in need of additional information concerning this
query.
Thanks,
ragingacademic-ga
References:
http://www.wdvl.com/Authoring/Scripting/WebWare/Server/
http://www.wdvl.com/Authoring/Scripting/WebWare/Client/
www.whatis.com
http://computer.howstuffworks.com/web-server.htm
http://computer.howstuffworks.com/web-page.htm
http://computer.howstuffworks.com/internet-infrastructure.htm |
