These issues are addressed in the next sections.
Database Domains
A domain name service allows hosts within a network to be hierarchically organized. Each node
within the organization is called a domain, and each domain is labeled by its function. These
functions may include COM for companies and EDU for schools. Each domain may have many
subdomains. Therefore, each host will be given a unique name within the network; its name
contains information about how it fits into the network hierarchy. Host names within a network
typically have up to four parts; the leftmost portion of the name is the host??™s name, and the rest
of the name shows the domain to which the host belongs.
For example, a host may be named HQ.MYCORP.COM. In this example, the host is named
HQ and identified as being part of the MYCORP subdomain of the COM domain.
The domain structure is significant for two reasons. First, the host name is part of the global
object name. Second, Oracle allows you to specify the DNS version of the host name in database
link names, simplifying the management of distributed database connections.
To use DNS names in database links, you first need to add two parameters to your initialization
file for the database. The first of these, DB_NAME, should be set to the instance name. The second
parameter, DB_DOMAIN, is set to the DNS name of the database??™s host or is set to WORLD by
default; the value cannot be NULL. DB_DOMAIN specifies the network domain in which the host
resides.
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