DataMart is the subset of datawarehouse. you can also consider datamart holds the data of one subject area. For an example you consider an organization that has HR Finance Communications and CorporateService divisions. For each division you can create a datamart. the historical data will be stored into datamarts first and then exported to datawarehouse finally.
Datamarts are the partitions of the overall datawarehouse. Datwarehouse covers as every aspect of the company's business then datamart is a subset of that huge datawarehouse.Datawarehouse is limited to the resource constraints and priorities of the MIS organization. But the task of the implementing Datwarehouse needs big effort and takes significant amount of time. It Impacts on return on investment.So the feasible option is to start a set of datamarts for each of the component departments.Simply we can say a set of small more managable databases are called datamarts.2 types of datamarts are there.1. Standalone datamarts: It enables a department or workgroup to implement a datamart with minimal or no impact on the Enterprise's operational database.2. Dependant datamarts: Enterprise database is required for these marts. Datasources includes operational databases and external sources of data.
Data marts are subset of data warehouse. It is the Repository of data designed to answer specific questions to a specific set of users. It is also subject oriented and an organization can have multiple data marts. It is also used for specific reporting and analysis.
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