Notes regarding web systems, servers and their applications. Client-server model, how pages work. URLs and their syntax, schemes, notes on HTML and CSS in detail. Internet layer abstraction, UDP and TCP, IP addressing for web pages, DNS, JavaScript in detail w/ jQuery. HTTP methods (GET, POST etc),...
1) What is a Client Server? Client-server model is a distributed application
structure that partitions tasks or workloads
between the providers of a resource or service,
called servers, and service requesters, called
clients.
Often clients and servers communicate over a
computer network on separate hardware, but
both client and server may reside in the same
system.
A server host runs one or more server programs,
which share their resources with clients.
A client usually does not share any of its
resources, but it requests content or service from a
server. Clients, therefore, initiate communication
sessions with servers, which await incoming
requests.
,2) How do web pages work? The browser sends an HTTP request message to
the server, asking it to send a copy of the website
to the client. This message, and all other data sent
between the client and the server, is sent across
an internet connection using TCP/IP.
▪ Hypertext documents are more
commonly known as web pages.
▪ Hypertext documents may link to
hypermedia documents, i.e., non-
hypertext documents (e.g. an
image, a video, a textual file
without any special structure).
▪ A web page or a hypermedia
document normally resides on a
remote computer (called a web
server) over the Internet so they
can be accessed by people from
anywhere in the world.
✓ Each web page or hypermedia
document has a web address, or
more formally a URL (Uniform
Resource Locator) which mainly
tells where it is.
▪ Web pages are written in a
markup language called HTML.
▪ Browsers display a web page by
reading and interpreting its HTML.
3) What is a URL? ▪ A Uniform Resource Identifier
(URI) is a string of characters used
to identify a resource
▪ The most common form of URI is
the Uniform Resource Locator
(URL), frequently referred to
informally as a web address, e.g.
https://developer.mozilla.org/en-US/
✓ Web browsers request pages
from web servers by using a URL
▪ Some URIs refer to a location
within a resource.
✓ This kind of URI ends with "#"
followed by an anchor identifier
(called the fragment identifier) – see next.
,4) What is the difference between a Relative An absolute URL contains all the information
and Absolute URL? necessary to locate a resource.
A relative URL locates a resource using an
absolute URL as a starting point. In effect, the
"complete URL" of the target is specified by
concatenating the absolute and relative URLs.
An absolute URL uses the following format:
scheme://server/path/resource
A relative URL typically consists only of the path,
and optionally, the resource, but no scheme or
server. The following tables define the individual
parts of the complete URL format.
Scheme = Specifies how the resource is to be
accessed.
Server = Specifies the name of the computer
where the resource is located.
Path =Specifies the sequence of directories
leading to the target. If resource is omitted, the
target is the last directory in path.
Resource = If included, resource is the target, and
is typically the name of a file. It may be a simple
file, containing a single binary stream of bytes, or
a structured document, containing one or more
storages and binary streams of bytes.
5) What are the different types of schemes? ❖ http: documents retrieved via a
protocol called HTTP.
❖ https: documents retrieved via a
protocol called HTTPS.
❖ file: documents accessible from
the local machine.
❖ ftp: documents retrieved via a
protocol called FTP.
, ❖ mailto: documents to be sent to the given
email address (emails)
6) What are the different types of URL Full syntax:
syntaxes? ✓
scheme:[//[[userinfo@]host[:port]]]
[path][?query][#fragment]
Two slashes (//): When the authority component
is absent, the path
component cannot begin with two slashes.
Authority:
✓ A naming authority for parsing
parts of the URL.
✓ userinfo (optional)
✓ host (mandatory)
❖ Domain name (or IP address) of
the web site (server).
❖ An optional authentication
section of a user name and
password, separated
by a colon, followed by @
❖ The passing of authentication
information in clear text has
proven to be
a security risk in almost every case where it has
been used.
Port (optional):
❖ Port number used by the
scheme (protocol).
• In programming, it may specify a particular
server program on a computer in a network.
Path:
✓ Location of the document on the
hosting machine (using “/” as the
path separator).
Query String:
✓ A list of data sent to the web
server, in the format
“name_1=value_1&…&name_n=value_n”.
✓ Typical URL containing a query
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