Web Technologies Understanding Part I





Internet
A global network that connecting the computers.
WWW(World Wide Web )
The World Wide Web (www) is an information space where documents and other web resources are identified by URLs, interlinked by hypertext links, and can be accessed via the Internet. It has become known simply as the Web
An information sharing model that is built on top of the Internet, utilizes HTTP,HTTPS protocol and browsers (such as Internet Explorer) to access Web pages formatted in HTML(example) that are linked via hyperlinks and the Web is only a subset of the Internet (other uses of the Internet include email (via SMTP), Usenet, instant messaging and file transfer (via FTP)
URL (Uniform Resource Locator)
The address of documents and other content on the Web. It is consisting of protocol, domain and the file. Protocol can be either HTTP, FTP, Telnet, News etc., domain name is the DNS name of the server and file can be Static HTML, DOC, Jpeg, etc., . In other words URLs are strings that uniquely identify resources on internet.
TCP/IP(Transmission Control Protocol/Internet Protocol )
Transmission Control Protocol/Internet Protocol  is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet).
The Internet protocol suite is the computer networking model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP, from Transmission Control Protocol (TCP) and the Internet Protocol (IP).
TCP/IP provides end-to-end connectivity specifying how data should be packetized, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.From lowest to highest, the layers are the link layer, containing communication technologies for a single network segment (link); the internet layer, connecting hosts across independent networks, thus establishing internet working; the transport layer handling host-to-host communication; and the application layer, which provides process-to-process application data exchange.
IP
Specifies the format of data packets and the addressing protocol.The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internet work. IP is a network layer protocol in the internet protocol suite. Aspects of IP are IP addressing and routing. Addressing refers to how end hosts become assigned IP addresses. IP routing is performed by all hosts, but most importantly by internet work routers
IP Address
A unique number assigned to each connected device, often assigned dynamically to users by an ISP on a session-by-session basis – dynamic IP address. Increasingly becoming dedicated, particularly with always-on broadband connections – static IP address.
Packet
A portion of a message sent over a TCP/IP Network. It contains content and destination

HTTP
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web. Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text.
HTTPS
Also called HTTP over TLS, HTTP over SSL, and HTTP Secure is a protocol for secure communication over a computer network which is widely used on the Internet. HTTPS consists of communication over Hypertext Transfer Protocol (HTTP) within a connection encrypted by Transport Layer Security or its predecessor, Secure Sockets Layer. The main motivation for HTTPS is authentication of the visited website and to protect the privacy and integrity of the exchanged data.
HTML (Hypertext Markup Language)
  • The authoring language used to create documents on the World  Wide Web
  • Hundreds of tags can be used to format and layout a Web page’s content and to hyperlink to other Web content
Hyperlink
Used to connect a user to other parts of a web site and to other web
sites and web-enabled services.

Web server
– A computer that is connected to the Internet. Hosts Web content
and is configured to share that content.
– Webserver is responsible for accepting HTTP requests from clients,
which are known as Web browsers, and serving them Web pages,
which are usually HTML documents and linked objects (images,
etc.).
Examples:
  • Apache HTTP Server from the Apache SoftwareFoundation.
  • Internet Information Services (IIS) from Microsoft.
  • Sun Java System Web Server from Sun Microsystems,formerly Sun ONE Web Server, iPlanet Web Server,and Netscape Enterprise Server.
  • Zeus Web Server from Zeus Technology
Web client
– Most commonly in the form of Web browser software such as
Internet Explorer or Netscape
– Used to navigate the Web and retrieve Web content from Web
servers for viewing.
Proxy server
– An intermediary server that provides a gateway to the Web (e.g.,
employee access to the Web most often goes through a proxy)
– Improves performance through caching and filters the Web
– The proxy server will also log each user interaction.
Caching
– Web browsers and proxy servers save a local copy of the
downloaded content – pages that display personal information
should be set to prohibit caching.
Web form
– A portion of a Web page containing blank fields that users can fill in
with data (including personal info) and submits for Web server to
process it.
Web server log
– Every time a Web page is requested, the Web server may
automatically logs the following information:
  • the IP address of the visitor
  • date and time of the request
  • the URL of the requested file
  • the URL the visitor came from immediately before
  • (referrer URL)
  • the visitor’s Web browser type and operating system

Cookies
– A small text file provided by a Web server and stored on a users PC
the text can be sent back to the server every time the browser
requests a page from the server. Cookies are used to identify a user
as they navigate through a Web site and/or return at a later time.
Cookies enable a range of functions including personalization of
content.
Session vs. persistent cookies
– A Session is a unique ID assigned to the client browser by a web
server to identify the state of the client because web servers are
stateless.
– A session cookie is stored only while the user is connected to the
particular Web server – the cookie is deleted when the user
disconnects
– Persistent cookies are set to expire at some point in the future –
many are set to expire a number of years forward
Socket
– A socket is a network communications endpoint.

Application Server
– An application server is a server computer in a computer network
dedicated to running certain software applications. The term also
refers to the software installed on such a computer to facilitate the
serving of other applications. Application server products typically
bundle middleware to enable applications to intercommunicate
with various qualities of service — reliability, security, nonrepudiation,
and so on. Application servers also provide an API to
programmers, so that they don't have to be concerned with the
operating system or the huge array of interfaces required of a
modern web-based application. Communication occurs through the
web in the form of HTML and XML, as a link to various databases,
and, quite often, as a link to systems and devices ranging from huge
legacy applications to small information devices, such as an atomic
clock or a home appliance.
– An application server exposes business logic to client applications
through various protocols, possibly including HTTP. the server
exposes this business logic through a component API, such as the
EJB (Enterprise JavaBean) component model found on J2EE (Java
2 Platform, Enterprise Edition) application servers. Moreover, the
application server manages its own resources. Such gate-keeping
duties include security, transaction processing, resource pooling,
and messaging
– Ex: JBoss (Red Hat), WebSphere (IBM), Oracle Application Server
10g (Oracle Corporation) and WebLogic (BEA)

Thin Client
– A thin client is a computer (client) in client-server architecture
networks which has little or no application logic, so it has to depend
primarily on the central server for processing activities. It is
designed to be especially small so that the bulk of the data
processing occurs on the server.

Thick client
– It is a client that performs the bulk of any data processing
operations itself, and relies on the server it is associated with
primarily for data storage.

Client-side scripting
– Generally refers to the class of computer programs on the web that
are executed client-side, by the user's web browser, instead of
server-side (on the web server). This type of computer
programming is an important part of the Dynamic HTML
(DHTML) concept, enabling web pages to be scripted; that is, to
have different and changing content depending on user input,
environmental conditions (such as the time of day), or other
variables.
– Web authors write client-side scripts in languages such as
JavaScript (Client-side JavaScript) or VBScript, which are based on
several standards:
o HTML scripting
o HTTP
o Document Object Model
  • Client-side scripts are often embedded within
an HTML document, but they may also be
contained in a separate file, which is referenced
by the document (or documents) that use it.
Upon request, the necessary files are sent to
the user's computer by the web server (or
servers) on which they reside. The user's web
browser executes the script, then displays the
document, including any visible output from
the script. Client-side scripts may also contain
instructions for the browser to follow if the
user interacts with the document in a certain
way, e.g., clicks a certain button. These
instructions can be followed without further
communication with the server, though they
may require such communication.

Server-side Scripting
– It is a web server technology in which a user's request is fulfilled by
running a script directly on the web server to generate dynamic
HTML pages. It is usually used to provide interactive web sites that
interface to databases or other data stores. This is different from
client-side scripting where scripts are run by the viewing web
browser, usually in JavaScript. The primary advantage to serverside
scripting is the ability to highly customize the response based
on the user's requirements, access rights, or queries into data
stores.
o ASP: Microsoft designed solution allowing various
languages (though generally VBscript is used) inside a
HTML-like outer page, mainly used on Windows but
with limited support on other platforms.
o ColdFusion: Cross platform tag based commercial
server side scripting system.
o JSP: A Java-based system for embedding code in
HTML pages.
o Lasso: A Datasource neutral interpreted programming
language and cross platform server.
o SSI: A fairly basic system which is part of the common
including a common menu.
apache web server. Not a full programming
environment by far but still handy for simple things
o PHP : Common opensource solution based on
including code in its own language into an HTML
page.
o Server-side JavaScript: A language generally used on
e client side but also occasionally on the server side.
o SMX : Lisplike opensource language designed to be
embedded into an HTML page.

Common Gateway Interface (CGI)
– is a standard protocol for interfacing external application software
with an information server, commonly a web server. This allows the
server to pass requests from a client web browser to the external
application. The web server can then return the output from the
application to the web browser.

Dynamic Web pages:
– can be defined as: (1) Web pages containing dynamic content (e.g.,
images, text, form fields, etc.) that can change/move without the
Web page being reloaded or (2) Web pages that are produced onthe-
fly by server-side programs, frequently based on parameters in
the URL or from an HTML form. Web pages that adhere to the first
definition are often called Dynamic HTML or DHTML pages.
Client-side languages like JavaScript are frequently used to produce
these types of dynamic web pages. Web pages that adhere to the
second definition are often created with the help of server-side
languages such as PHP, Perl, ASP/.NET, JSP, and languages. These
server-side languages typically use the Common Gateway Interface
(CGI) to produce dynamic web pages.

Digital Certificates
In cryptography, a public key certificate (or identity certificate) is a certificate
which uses a digital signature to bind together a public key with an identity —
information such as the name of a person or an organization, their address, and
so forth. The certificate can be used to verify that a public key belongs to an
individual.
In a typical public key infrastructure (PKI) scheme, the signature will be of a
certificate authority (CA). In a web of trust s
"endorsements"). In either case, the signatures on a certificate are attestations by
the certificate signer that the identity information and the public key belong
together.
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Certificates can be used for the large-scale use of public-key cryptography.
Securely exchanging secret keys amongst users becomes impractical to the point
of effective impossibility for anything other than quite small networks. Public key
cryptography provides a way to avoid this problem. In principle, if Alice wants
others to be able to send her secret messages, she need only publish her public
key. Anyone possessing it can then send her secure information. Unfortunately,
David could publish a different public key (for which he knows the related private
key) claiming that it is Alice's public key. In so doing, David could intercept and
read at least some of the messages meant for Alice. But if Alice builds her public
key into a certificate and has it digitally signed by a trusted third party (Trent),
anyone who trusts Trent can merely check the certificate to see whether Trent
thinks the embedded public key is Alice's. In typical Public-key Infrastructures
(PKIs), Trent will be a CA, who is trusted by all participants. In a web of trust,
Trent can be any user, and whether to trust that user's attestation that a
particular public key belongs to Alice will be up to the person wishing to send a
message to Alice.
In large-scale deployments, Alice may not be familiar with Bob's certificate
authority (perhaps they each have a different CA — if both use employer CAs,
different employers would produce this result), so Bob's certificate may also
include his CA's public key signed by a "higher level" CA2, which might be
recognized by Alice. This process leads in general to a hierarchy of certificates,
and to even more complex trust relationships. Public key infrastructure refers,
mostly, to the software that manages certificates in a large-scale setting. In X.509
PKI systems, the hierarchy of certificates is always a top-down tree, with a root
certificate at the top, representing a CA that is 'so central' to the scheme that it
does not need to be authenticated by some trusted third party.
A certificate may be revoked if it is discovered that its related private key has
been compromised, or if the relationship (between an entity and a public key)
embedded in the certificate is discovered to be incorrect or has changed; this
might occur, for example, if a person changes jobs or names. A revocation will
likely be a rare occurrence, but the possibility means that when a certificate is
trusted, the user should always check its validity. This can be done by comparing
it against a certificate revocation list (CRL) — a list of revoked or cancelled
certificates. Ensuring that such a list is up-to-date and accurate is a core function
in a centralized PKI, one which requires both staff and budget and one which is
therefore sometimes not properly done. To be effective, it must be readily
available to any who needs it whenever it is needed and must be updated
frequently. The other way to check a certificate validity is to query the certificate
authority using the Online Certificate Status Protocol (OCSP) to know the status
of a specific certificate.
Both of these methods appear to be on the verge of being supplanted by XKMS.
This new standard, however, is yet to see widespread implementation.
A certificate typically includes:
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The public key being signed.
A name, which can refer to a person, a computer or an organization.
A validity period.
The location (URL) of a revocation center.
The most common certificate standard is the ITU-T X.509. X.509 is being
adapted to the Internet by the IETF PKIX working group.
Classes
Verisign introduced the concept of three classes of digital certificates:
Class 1 for individuals, intended for email;
Class 2 for organizations, for which proof of identity is required; and
Class 3 for servers and software signing, for which independent verification and
checking of identity and authority is done by the issuing certificate authority (CA)

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