Refresh techniques may also depend on the characteristics of
the source and the capabilities of the database servers.
Extracting an entire source file or database is usually too
expensive, but may be the only choice for legacy data
sources. Most contemporary database systems provide
replication servers that support incremental techniques for
propagating updates from a primary database to one or more
replicas. Such replication servers can be used to
incrementally refresh a warehouse when the sources change.
There are two basic replication techniques: data shipping and
transaction shipping