Importance of <Lastmod> attribute in Google Sitemap

Please Help.....

[Cyclob]

Hi...

I just created an XML file of my site for google sitemap but I have some question about it. This is the type that I saw in the example provided in Google sitemap's guidelines

<url>
<loc>http://www.mysite.com/</loc>
<lastmod>2005-09-20</lastmod>
</url>

I'm wondering that if I submit first time to google and it shows the Last modify date (as in example above). When google come to download the file next time and the date hasn't been changed, Will Google still index the information in that page?

Or if Google see it's the same date as they came last time, and they will ignore and not index the page?

And what about if I don't put the <lastmod> attribute, just the url only, for example...

<url>
<loc>http://www.mysite.com/</loc>
</url>

Would this be okay?

Please help this out because I'm not quite fully understand on what exactly Google want.

Thank you in advance

[webspy]

In theory, Google will see that you updated the page (lastmod changed) and then Google will crawl it again to get the new content.
When the lastmod has not changed Google will not crawl the page again. This has nothing to do with keeping pages indexed or not.

[mycutegoddess]

Is it effect with freshness of document?

If Google visit our page and see it's not update will google decrease ranking of our page?

[Phil_Payne]

> When the lastmod has not changed Google will not crawl the page again. This has nothing to do with keeping pages indexed or not.

That seems to be how it's working, though many on the Usenet groups disagree.

It's fine by me. It saves Google and myself bandwidth, and I can make minor cosmetic changes without pushing Google blindly through the reindexing process when there's no point.