A data mart is a repository of data that is designed to serve a particular community of knowledge workers.
The difference between a data warehouse and a data mart can be confusing because the two terms are sometimes used incorrectly as synonyms. A data warehouse is a central repository for all an organization's data. The goal of a data mart, however, is to meet the particular demands of a specific group of users within the organization, such as human resource management (HRM). Generally, an organization's data marts are subsets of the organization's data warehouse.
Because data marts are optimized to look at data in a unique way, the design process tends to start with an analysis of user needs. In contrast, a data warehouse's design process tends to start with an analysis of what data already exists and how it can be collected and managed in such a way that it can be used later on. A data warehouse tends to be a strategic but somewhat unfinished concept; a data mart tends to be tactical and aimed at meeting an immediate need.
Today, data virtualization software can be used to create virtual data marts, pulling data from disparate sources and combining it with other data as necessary to meet the needs of specific business users. A virtual data mart provides knowledge workers with access to the data they need while preventing data silos and giving the organization's data management team a level of control over the organization's data throughout its lifecycle.