NS Cache

[pyh at mail.nsbeta.info]

I'm reading the document "Secure DNS Deployment Guide" got from the URL a 
poster gave in the list. 

The document said: 

When a user types the URL www.example.com into a Web browser, the browser 
program contacts a type of resolver called a stub resolver that then 
contacts a local name server (called a recursive name server or resolving 
name server). The resolving name server will check its cache to determine 
whether it has valid information (the information is determined to be valid
on the basis of criteria described later in this document) to provide IP 
address for the accessed Internet resource 
(i.e.,www.marketing.example.com). If not, the resolving name server checks 
the cache to determine whether it has the information regarding the name 
server for the zone marketing.example.com (since this is the zone that is 
expected to contain the resource www.marketing.example.com). If the name 
server!ˉs IP address is in the cache, the resolver!ˉs ne query will be 
directed against that name server. If the IP address of the name server of 
marketing.example.com is not available in the cache, the resolver 
determines whether it has the name server information for a zone that is 
one level higher than marketing.example.com (i.e., example.com). If the 
name server information for example.com is not available, the next search 
will be for the name server of the .com zone in the cache. 


I think the statement below is wrong? 

> If not, the resolving name server checks the cache to determine whether it > has the information regarding the name server for the zone 
> marketing.example.com (since this is the zone that is expected to contain > the resource www.marketing.example.com). 
 

How does the resolver know www.marketing.example.com is a domain name or a 
zone? www.marketing.example.com can also be a zone which has valid NS 
records. So I was thinking the resolver shall check the cache firstly to 
see whether it has the NS records for the zone www.marketing.example.com, 
if not, then to check the NS for marketing.example.com. Am I right? 

Regards.