When people visit a website, they may not see the most recently
updated pages, because their computer may simply bring up pages that
were stored in their own browser?s cache during a previous visit to
the site.

My question: Is there something savvy webmasters can do to make sure
that visitors to their site see the latest updates, and not material
stored in the visitor's own cache?  I somehow have the feeling that
this problem occurs only at the less professional websites.

A satisfactory answer doesn?t have to provide detailed technical
information on how to avoid this problem, merely (a) an authoritative
yes or no as to whether or not there is a solution, with a few
references or links; and (b) a short, general description of one or
more solutions to this problem.  An unacceptable solution: A notice at
the site reminding people to clear their cache.

Hi curiousndc,

Good day and thanks for your question.

The answer to question (a) is an emphatic yes. There are a few ways to
ensure that the user has the latest content. I'll describe the two
most common ones.

(a) The usage of tags that tell the browser not to cache the page. For
plain static html pages, the usage of the following two META tags
within the HEAD section ensures this:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="-1">

In case you're using ASP, the following is the equivalent for the above:
<% Response.CacheControl = "no-cache" %>>
<% Response.AddHeader "Pragma", "no-cache" %> 
<% Response.Expires = -1 %>


(b) Using sessions. This is a more advanced technique used by
'professional' web sites. The URL generated is unique each time since
it includes time information. These are normally implemented using
JSP,ASP,PHP etc...

I hope this answered your question.

If you have any clarifications, pleae don't hesitate to ask.

Thank you for using this service and have a nice day.

With regards,
aditya2k

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Request for Answer Clarification by curiousndc-ga on 18 Feb 2005 03:06 PST

Thanks.  For the most part your answer more than meets my needs, and I
appreciate the specific suggestions in part (a) of your answer.  I
would, however, still like a couple references or links to reputable
sites where I can read up more on this issue.

Also ? and this wasn?t in my original question, so I don?t require an
answer, but would appreciate it:  The regularly updated web pages in
question are in PDF.  Is your answer to my primary question still an
?emphatic yes??  And would the code differ from what you suggested for
html pages?

Thanks!!

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Request for Answer Clarification by curiousndc-ga on 19 Feb 2005 15:09 PST

To aditya2k:  

Can you let me know whether or not you're planning on providing the
references or links I asked for in my original question and in my
?request for answer clarification??  Thanks.

---

Clarification of Answer by aditya2k-ga on 21 Feb 2005 17:09 PST

Hi,

Sorry for the delay. I was out of town for the long weekend.

Here is a link from Microsoft detailing on how to prevent caching in
Internet Explorer. They explain why the Pragma statement alone does't
prevent caching in IE.
http://support.microsoft.com/kb/q234067/

As far as Netscape and Mozilla is concerned, the Pragma statement by
itself will work.

As far as PDF is concerned, you will have to chnge the http headers at
the server side when delivering PDF. I will do a little more ersearch,
and if I come across anything, I will post it here.

Once again, sorry for the delay in replying.

Thanks,
aditya2k