Since locks don??™t escalate, Oracle is also extremely appropriate
for near real-time data feeds into the warehouse in a scenario not unlike OLTP
workloads.
Warehousing usage characteristics lead to deploying different types of schema. In
OLTP databases, transaction data is usually stored in multiple tables and data items
are stored only once. If a query requests data from more than one transaction table,
the tables are joined together. Typically, the database query optimizer decides which
table to use as the starting point for the join, based on the assumption that the data
in the tables is essentially equally important.
Data Warehouse Design | 229
Although Oracle-based data warehouses are sometimes modeled as third normal
form (3NF) (described in Chapter 4), when business users need an understandable
schema to formulate their own ad hoc queries or analytical processing is required,
key transaction data can be more appropriately stored in a central fact table, surrounded
by dimension or lookup tables, as shown in Figure 10-2.
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