A Data Mart is a subset of a data warehouse that is focused on a specific subject area or department within an organization. It contains a collection of fact tables, dimension tables, and other relevant data that is specifically tailored to meet the reporting and analysis needs of a particular business unit or user group.
In your case, if you have four fact tables in your data warehouse related to HR, namely Fact_Employee_Entrance_Exits, Fact_Employee_Leaves, Fact_Employee_Reviews, and Fact_Employee_Compensation, you can indeed consider creating separate Data Marts for different departments.
Based on your description, it makes sense to have one Data Mart focused on HR, which would include the first three fact tables (Fact_Employee_Entrance_Exits, Fact_Employee_Leaves, Fact_Employee_Reviews). This HR Data Mart would serve as a dedicated reporting and analysis environment for the HR department, providing them with the necessary information about employee entrance and exits, leaves, and reviews.
Similarly, the Fact_Employee_Compensation fact table can be part of a separate Data Mart that caters specifically to the Financial Department. This Financial Data Mart would contain the necessary dimensions and other relevant data required for financial analysis and reporting related to employee compensation.
By creating separate Data Marts, you can provide more focused and tailored data sets to different user groups or departments, enabling them to perform their analysis and reporting more efficiently. It also helps in controlling data access and ensuring that each department gets the data relevant to their specific needs.