Derived data: selected, formatted, and aggregated for end-user decision support applications Derived data are stored in each of the data marts. Reconciled data: detailed, current data intended to be the single, authoritative source for all decision support. Reconciled data are stored in the enterprise data warehouse and an operational data store. Operational data: stored in the various operational systems of record throughout the organization. Three-Layer Data Architecture of data warehouses
Agenda ➢ Concept of Data Warehousing ➢ Data Warehousing Architecture ➢ Characteristics of Data Warehouse Data ➢ Data Integration and ETL process ➢ The Star Schema ➢ Variations of the Star Schema
Data Characteristics: Status vs. Event Data Data in data warehouses have characteristics different from operational databases. Figure 9-6 Example of DBMS log entry The figure represent a bank account data before and after a transaction ($50 withdrawal ). The before and after image are Status data. Status data would typically be stored in an operational database . The Update represents an Event data. An event data is a database action (create/update/delete) that results from a transaction . Transactions are often recorded in data warehouses in the form of a database log.