Chapter 1. ETL Primer
The introduction of this book described the need for data integration. This chapter provides a starting point to the wonderful world of data integration and explains the differences and similarities among the three main forms of data integration: ETL, ELT, and EII. To fully understand the reasoning behind using a data warehouse and an ETL solution to load and update data, we start by explaining the differences between a transaction and an analysis database.
OLTP versus Data Warehousing
The first question one might ask is how source data systems differ from business intelligence (BI) systems (sometimes still called decision support systems or DSS). An individual transaction system, often denoted by the acronym OLTP (short for OnLine Transaction Processing), needs to be able to very quickly retrieve a single record of information. When multiple records are needed they are usually tied to a single key that has been retrieved before. Think of an order with the accompanying order lines in an order entry system or a personnel record with all salary and bonus information in an HR system. What's more: this data often needs to be updated as well, usually just one record at a time.
The biggest difference between an OLTP and a BI database (the data warehouse, or DWH) is the amount of data analyzed in a single transaction. Whereas an OLTP handles many concurrent users and queries touching only a single record or limited groups of records at a time, a data warehouse must have ...