Distinguish between Centralized Database Design and Decentralized Database Design.
Centralized Database Design:
For a small organization and limited scope of operations, the database may be small in terms of data. Therefore, the database design may be relatively simple and can be easily done by one group of designer or even a single person. This is called centralized design of database. The designer can study the system processes, identify the constraints, and create conceptual schema, whereas the users can verify it to ensure that the database meets their needs and processing requirements.
Decentralized Database Design:
When the database study reveals that the resulting database is for the ‘whole organizations and that it has large number of entities and complex relations on which very complex operations are performed, then the database design may be undertaken by division of work. Here it may be suitable to study and design conceptual schema for each department or function for which the database is to be designed. The database design project may be thought of as one large project subdivided into smaller modules, and each module is designed by a group of people.
Each module is in itself a system and must meet the system requirements as a whole. These modules when integrated to form a single database must meet the processing requirements. This is called decentralized design approach. This approach is also suitable when the database design is spread across several operational sites, and each element is a subset of the entire data set.