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and also supports the inclusion of the time. ISO 8601 is very nicely described at

http://

www.iso.org/iso/en/prods-services/popstds/datesandtime.html

.

?

<changefreq>

tells Google how often the page changes. The possible values are

always

(for

pages that change with each request),

hourly

,

daily

,

weekly

,

monthly

,

yearly

, and

never

.

?

<priority>

lets you tell Google how you evaluate the importance of individual pages of your

web site as compared to the others. The value is a number between 0.0 and 1.0. Please note that

the

<priority>

element only has significance over the relative importance of pages

within

a

web site, and it

does not

affect the overall ranking of a web site!

Using Yahoo! Sitemaps

Yahoo!’s sitemap protocol is considerably simpler than Google’s protocol. It too supports several for-

mats including news feeds, but the format discussed here is the flat URL list plaintext file. It does not

utilize XML, nor does it ask for any information other than a list of URLs delimited by linefeeds. Yahoo!

requires that a file named

urllist.txt

appear in the root directory of a web site, and that you register

a Yahoo! account with them.

The site must then be added at

http://submit.search.yahoo.com/free/request

. Arguably, Yahoo!

accomplishes some of what Google does with its simpler approach — though it does not accept informa-

tion regarding last modified dates, estimates of update frequency, or the relative importance of the pages.

Yahoo! also cannot be pinged regarding sitemap updates.

The Yahoo! sitemaps equivalent of the previously shown Google sitemap would be a file named

urllist.txt

in the root directory of a web site with the following contents:

http://www.cristiandarie.ro/

http://www.cristiandarie.ro/books/

http://www.cristiandarie.ro/forthcoming/

Like Google, using Yahoo!’s sitemap protocol will not influence a web site’s rankings, but it may get a

site spidered more quickly.

Generating Sitemaps Programmatically

It would be useful to have a library that can create Yahoo! and Google sitemaps programmatically using

the same information. The exercise that follows demonstrates such a library.

You’ll create a class named

Sitemap

, which can store a number of links from your site, and generate the

associated Yahoo! and Google sitemap files for you. (The notion of

class

, as well as the basic notions of

object-oriented programming with PHP, was explained in Chapter 7, when you used it for the first time

in this book.)

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Chapter 9: Sitemaps

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