The
placeholder domain model, also known as the sterile parent domain
model, deserves special mention because of its combination of a single
namespace/multiple domain model and the peer-root model. Simply put, the
placeholder domain model, shown in Figure 1,
is composed of an unoccupied domain as the forest root, with multiple
subdomains populated with user accounts and other objects.
There are two
distinct advantages to this design. First, as with the peer-root model,
the schema is separate from the user domains, thus limiting their
exposure and helping to protect the schema. Second, the namespace for
the user accounts is consistent in the namespace, thus mitigating any
potential political issues. In other words, because all users in all
locations are at the same logical level in the domain structure, no one
group will feel superior or inferior to another. This issue might seem
trite, but the psychological nature of humans is finicky, and you might
find that this design offers advantages for certain organizations.
Examining a Placeholder Domain Real-World Design Example
CompanyE
is an architectural firm with major offices located in New York,
Chicago, Los Angeles, San Paulo, Rio de Janeiro, Berlin, Paris, London,
Tokyo, Singapore, and Hong Kong. Administration is centralized in New
York, but regional administration takes place in Rio de Janeiro, London,
and Tokyo. The company has recently migrated to AD DS and has chosen to
deploy a placeholder domain model for its organization that looks
similar to Figure 2.
All users
authenticate to geographically centric subdomains. In addition, the
administrators in New York have segregated the schema master function
into the placeholder domain, limiting its exposure and have limited
access to this domain to a small group of high-level administrators.
Each domain is logically oriented as well, to give the impression of
autonomy to each geographical unit.
