Mapping is a process of converting on level to another level. There are two levels of mapping: • From the conceptual level to the internal level • From the external level to the conceptual level Conceptual / Internal Mapping: The conceptual/internal mapping defines the association between the abstract view and stored database. It specifies how conceptual records and fields are represented... 

Database can he viewed at three levels. The levels form three-level architecture and are depicted by three models. The models refer to the permanent structure of the database, not to the data that is stored at any given moment. A database model is a collection of tools. It may include a type of diagram and specialized vocabulary for describing the structure of the database. The purpose of the three-level... 

Dr. E. F. Codd worked to improve the working of DBMSs for handling large volumes of data. He applied the rules of mathematics for solving the problems of earlier database models. Some important problems were: • Data integrity • Data redundancy Dr. Codd presented a paper “A Relational Model of Data for Large Shared Databanks” in June I 970 that contained 12 rules. A DBMS that satisfies these... 

To overcome the problems of the hierarchical data model, the Network Model was developed. The network model modified the hierarchical model by allowing multiple parent-child relationships. These relationships are known as sets in a network model. The network model structures and language constructs were defined by the CODASYL (Conference on Data Systems Language). The Network Model 1. Characteristics...