Legacy system: means old technology used in systems or old computer software or applications. Now tern legacy database system means that all the historical overview of database systems what kind of models and navigation systems were present in a database system. Before moving on to the historical overview it is important to know the introduction of the database system in all details, so we will move on to the details of its model. Database: The term database generally refers to the organized collection of well-defined data. Database Management Systems (DBMS): Database Management Systems (DBMS) are user-built software that interacts with the user and the database itself to capture and analyze all data. Normally DBMS is a software system designed for creating, querying, updating and administering databases. Some well-known databases are MySQL, MariaDB, PostgreSQL, SQLite, Microsoft SQL Server, Oracle, FoxPro, FileMaker Pro. The database generally cannot interact with different database management systems, but different database management systems such as SQL and ODBC or JDBC can allow a single database to interact with multiple database management systems. Databases are designed to handle all types of information by storing, retrieving, and managing that information. Databases are made so that the user can interact with the databases themselves. The DBMS is usually responsible for maintaining all the data in a system, and if that data is lost, the DBMS will restore the data itself. Databases are used for business operations, but an increasing number of database systems are usually built for more stable interaction with users. Some users of database applications are end users, which means they are not familiar with any of its computing applications that... are middle of paper... were used to communicating with information in information stores in such a way that the information could be effectively shortened using online exposure management or OLAP questions. In the dimensional model, the database structure comprises a vast solitary table of truths represented using dimensions and measures. A dimension provides the setting of a certainty, (for example, when and where it occurred, and its writing) and is used within investigations to assemble related realities together. The dimensions tend to be discrete and are regularly hierarchical; for example, the area can incorporate the building, the state, and the nation. A measure is an amount that represents the truth, such as income. It is essential that the measures are definitively cumulated, for example revenues from different sectors could be included. Now we will talk about the main and important databases