 Welcome back MechanicalEI. Did you know that data independence is the type of data transparency that matters for a centralized DBMS? This makes us wonder, what is data independence? Before we jump in, check out the previous part of this series to learn about what a database management system is. Now, data independence refers to the immunity of user applications to changes made in the definition and organization of data. It is essential because application programs should not be exposed to the details of data representation and storage. There are two types of data independence. First is the logical data independence, which is the ability to change the logical schema without changing the user point of view. For example, the addition or removal of new entities, attributes or relationships to the logical schema are having to rewrite existing application programs. Second is physical data independence, which is the ability to change the physical schema without changing the logical schema. For example, a change to the internal schema such as using different file organization or storage structures or storage devices should be possible without having to change the conceptual or external schemas. The design of a DBMS depends on its architecture. A three-tire architecture is the most widely used architecture to design a DBMS and, as the name suggests, consists of the following three tires. First is a database tier. At this tier, the database resides along with its query processing languages and their respective relations. Second comes the application tier. This tier holds the application server and the programs that access the database. End users are unaware of any existence of the database beyond the application tier. At the other end, the database tier is not aware of any other user beyond the application tier. Finally comes the user tier. All end users operate on this tier. At this tier, multiple views of the database can be provided by the application. All views are generated by applications that reside in the application tier. Hence, we first saw what data independence is and then went on to see what DBMS system architecture is. In the next episode of MechanicalEI, find out what database modeling is.