3 tier client server architecture
•Common web application.
•Middle layers is called web server or application server.
Acts like a connections for sending data between the database server and the client.
•Security – encrypt data at the server before transmission and decrypt data at the client.
Data Models
•Data Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey.
•Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations
Categories of data models
•Conceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.)
•Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer.
•Implementation (representational) data models: Provide concepts that fall between the above two, balancing user views with some computer storage details.Data Models
Data Models
•Object-Relational Models:
Most Recent Trend. Started with Informix Universal Server. Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server etc. systems