A sitemap is  an XML file,that lists the URLs of a site.  The sitemap file can be used to inform search engines like google on the pages available on a site and when those pages have been modified.  The search engines require a particular format for the sitemap xml file. Let me give a brief on sitemap creation for google.

Create an xml file(say sitemap.xml). Its better to create the xml file dynamically using the scripting language like php, jsp etc.

Format of sitemap xml  accepted by google:

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.google.com/schemas/sitemap/0.84" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.google.com/schemas/sitemap/0.84 http://www.google.com/schemas/sitemap/0.84/sitemap.xsd">
<url>
<loc>http://domain.tld/</loc>
<lastmod>2008-01-01</lastmod>
<changefreq>daily</changefreq>
<priority>0.1</priority>
</url>
</urlset>

The points to be remembered when creating a sitemap are:

1. Sitemap should start with the tag <urlset> and end with </urlset>
2. Each set of xml entry shouild start with <url> and end with </url>
3. <loc></loc> contains the url
4. The <lastmod> tag expects a date in the  format YYYY-MM-DD,  or the date format can be in w3c format.
5. The <changefreq> tag expects one of the  values: always, hourly, daily, weekly, monthly etc.
6. The <priority> can be a value between 1.0 and 10

7. Replace special charecters from xml file.
Character                   Replacement
Ampersand     &         &amp;
Single Quote    ‘         &apos;
Double Quote  “         &quot;
Greater Than   >        &gt;
Less Than       <        &lt;

8. Encoding should be UTF-8 mode
9. The maximum permitted size of a sitemap file is 10 MB.

Sample PHP  code for sitemap generation:

$xml = '';
$xml =  "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"."\n";
$xml .= "<urlset xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xsi:schemaLocation=\"http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd\" xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">"."\n";
for($i=0;$i<$subLimit;$i++){
$title = str_replace("&","&amp;",strip_tags($response['title']));
$loc = str_replace("&","&amp;",strip_tags($response['location']));
$com = str_replace("&","&amp;",strip_tags($response['company']));
//$loc1 = $row['job_jobs_location'];
$title = htmlentities($title, ENT_QUOTES, "UTF-8");
$com = htmlentities($com, ENT_QUOTES, "UTF-8");
$loc = htmlentities($loc, ENT_QUOTES, "UTF-8");
$date = $response['date'];
$date = strtotime($date);
$date = date(DATE_W3C, $date);   //Date in w3c format
$xml .= "<url>"."\n";
$xml .= "<loc>http://www.jobtreks.com/jobresult/$title/$com/$loc/$id</loc>"."\n";
$xml .= "<lastmod>$date</lastmod>"."\n";
$xml .= "<priority>0.50</priority>"."\n";
$xml .= "<changefreq>weekly</changefreq>"."\n";
$xml .= "</url>"."\n";}
$xml .= "</urlset>";
$fh = fopen('sitemap.xml', 'w'); //After exceuting this file, an xml file called sitemap.xml is created.

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