1. Levels of Abstraction (Views of Data ) Physical level: describes how a record (e.g., customer) is stored. Logical level: describes data stored in database, and the relationships among the data. type customer = record customer_id : string; customer_name : string; customer_street : string; customer_city : integer; end; View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.

2. View of Data An architecture for a database system

3. DATA MODELING AND ITS COMPONENTS Data Modeling In computer science, data modeling is the process of structuring and organizing data.In computer science, data modeling is the process of structuring and organizing data. These data structures are then typically implemented in a database management system. These data structures are then typically implemented in a database management system. In addition to defining and organizing the data, In addition to defining and organizing the data, data modeling may also impose constraints or limitations on the data placed within the structuredata modeling may also impose constraints or limitations on the data placed within the structure

4. Managing large quantities of structured and unstructured data is a primary function of information systems.Managing large quantities of structured and unstructured data is a primary function of information systems. Data models describe structured data for storage in data management systems such as relational databases. Data models describe structured data for storage in data management systems such as relational databases. They typically do not describe unstructured data, such as word processing, documents, email messages, pictures, digital audio, and video. They typically do not describe unstructured data, such as word processing, documents, email messages, pictures, digital audio, and video.

5. Data model Data model fall into three different groups.Data model fall into three different groups. 1.Object based logical model. 2.Record based logical model. 3.Physical model Object based logical model object based logical model are used in describing data at the logical and view level.object based logical model are used in describing data at the logical and view level. They are characterized by the fact that they provide fairly flexible structuring capabilities and allow data constrains to a specified explicity. They are characterized by the fact that they provide fairly flexible structuring capabilities and allow data constrains to a specified explicity.

6. Record Based Logical Model Record based logical model used in describing data at the logical and view level.Record based logical model used in describing data at the logical and view level. In contrast to object based data models they are used both to specify the overall logical structures of the data base and to provide a higher level description of the implementation.In contrast to object based data models they are used both to specify the overall logical structures of the data base and to provide a higher level description of the implementation. Record based models are so named because the database is structured in fixed format records of several types. Each record type defines a fixed number of fields, or attributes, and each field is usually fixed lengthRecord based models are so named because the database is structured in fixed format records of several types. Each record type defines a fixed number of fields, or attributes, and each field is usually fixed length The three most widely accepted record based data models are 1. Relational Model 2. Network Model 3. Hierarchical Model.

7. RELATIONAL MODEL Relational model uses a collection of tables to represent both data and the relationship among those data. Each table has multiple columns and each column has a unique name.Relational model uses a collection of tables to represent both data and the relationship among those data. Each table has multiple columns and each column has a unique name. Student code name k101raja s102geeta Table Name: Student Course code Course name C21agronomy C32maths C33economics C50extension C81horti C86pathology Table Name: Course

8. NETWORK MODEL Data in the network model are represented by collection of records and relation ship among data are represented by links, which can be viewed as pointers.Data in the network model are represented by collection of records and relation ship among data are represented by links, which can be viewed as pointers. The records in the database are organized as collection of arbitary graphs. The records in the database are organized as collection of arbitary graphs.

9. K101 Rajat Kataria c32c32 math s C34AEX c21c21 AG R C50ENT S102Geet a Subr ama nian C33AEC C81HOR C86PAT 9656 88 6976 9289 82 9296

10. HIERARCHICAL MODEL. Hierarchical model is similar to the network model in the sense that data and relationship among data are represented by records and links, respectively.Hierarchical model is similar to the network model in the sense that data and relationship among data are represented by records and links, respectively. It differs from Network model in the records are organized as collection of trees rather then arbitrary graphs.It differs from Network model in the records are organized as collection of trees rather then arbitrary graphs.

11. Student code stu.nameStudent code stu.name Course code, cou.name, marks k101raja C21agro nom y 88 c32maths96 c33economics69 c34extension56 c50entomology76