Being designed for the enterprise so that everyone has a common data set, they are large and increase in size with time. Typical storage sizes run from 50 gigabytes to over a terabyte. Because of the large size, some firms are using parallel computing to speed data retrieval. A data mart is a small warehouse designed for the SBU or department level. It is often a way to gain entry and provide an opportunity to learn.
Data warehouses are a major industry.
Estimates vary but it is clear that many more than half of the Fortune 500 have data warehouse projects underway or planned. On-line Analytical Processing This term, abbreviated OLAP, was introduced by E.F. Codd, the father of relational databases in 1993 in a major article in Computerworld. Codd came to the conclusion that relational databases for OLTP had reached the maximum of their capabilities in terms of the views of the data they provided the user. The problem stemmed principally from the massive computing required when relational data bases were asked to answer relatively simple SQL queries. The basic idea in OLAP is that managers should be able to manipulate enterprise data models across many dimensions to understand changes that are occurring.