Page 226 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 11: Programming Process

Notes
Speeding up the Internet is an ongoing discussion over the use of peering and QoS technologies.
Guidelines for Web response times are:
(i) 0.1 second (one tenth of a second). Ideal response time. The user doesn’t sense any
interruption.
(ii) 1 second. Highest acceptable response time. Download times above 1 second interrupt the
user experience.
(iii) 10 seconds. Unacceptable response time. The user experience is interrupted and the user
is likely to leave the site or system.

11.4.12 Caching
If a user revisits a Web page after only a short interval, the page data may not need to be re-
obtained from the source Web server. Almost all web browsers cache recently obtained data,
usually on the local hard drive. HTTP requests sent by a browser will usually only ask for data that
has changed since the last download. If the locally cached data are still current, it will be reused.
Caching helps reduce the amount of Web traffic on the Internet. The decision about expiration is
made independently for each downloaded file, whether image, stylesheet, JavaScript, HTML, or
whatever other content the site may provide. Thus even on sites with highly dynamic content,
many of the basic resources only need to be refreshed occasionally. Web site designers find it
worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that
they can be cached efficiently. This helps reduce page download times and lowers demands on
the Web server.
There are other components of the Internet that can cache Web content. Corporate and academic
firewalls often cache Web resources requested by one user for the benefit of all. (See also Caching
proxy server.) Some search engines also store cached content from websites. Apart from the
facilities built into Web servers that can determine when files have been updated and so need
to be re-sent, designers of dynamically generated Web pages can control the HTTP headers sent
back to requesting users, so that transient or sensitive pages are not cached. Internet banking and
news sites frequently use this facility. Data requested with an HTTP ‘GET’ is likely to be cached
if other conditions are met; data obtained in response to a ‘POST’ is assumed to depend on the
data that was POSTed and so is not cached.
Web caching is the caching of web documents (e.g., HTML pages, images) to
reduce bandwidth usage, server load, and perceived lag. A web cache stores
copies of documents passing through it; subsequent requests may be satisfied
from the cache if certain conditions are met.

The Issue

ight of the top 50 e-services consulting, creative, and technology companies joined to
form this client company — eight separate companies with eight separate sales forces
Ecombined into one. Our contact was the CEO of the largest company. He understood
that a sale is a process and that to effect a smooth merger, the newly combined sales teams
would need to be on the same page with a common sales methodology. When our contact
was appointed EVP for corporate development for the newly formed company, he knew
that he had to bring these eight companies together through common language and process.

Contd...

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