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Introduction - Basic Models of Database Systems Purpose of Database Systems

The document discusses the purpose and advantages of database systems over file systems for storing data. It notes common issues with using file systems like data redundancy, difficulty accessing data, and integrity and security problems. It then outlines three levels of abstraction in databases - physical, logical, and view level. Finally, it provides an overview of different data models used for database design including the relational, entity-relationship, object-based, and semi-structured models.

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62 views4 pages

Introduction - Basic Models of Database Systems Purpose of Database Systems

The document discusses the purpose and advantages of database systems over file systems for storing data. It notes common issues with using file systems like data redundancy, difficulty accessing data, and integrity and security problems. It then outlines three levels of abstraction in databases - physical, logical, and view level. Finally, it provides an overview of different data models used for database design including the relational, entity-relationship, object-based, and semi-structured models.

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14CS440 / Database Management Systems 2018

Introduction – Basic Models of Database Systems

Purpose of Database Systems

 In the early days, database applications were built directly on top of file
systems

 The drawbacks of using file systems to store data:

1. Data redundancy and inconsistency


- Multiple file formats, duplication of information in different files
2. Difficulty in accessing data
- Need to write a new program to carry out each new task
3. Data isolation
- Multiple files and formats
4. Integrity problems
- Hard to add new constraints or change existing ones
5. Atomicity of updates
- Example: Transfer of funds from one account to another should
Either complete or not happen at all
6. Concurrent access by multiple users
- Uncontrolled concurrent accesses can lead to inconsistencies
7. Security problems
- Hard to provide user access to some, but not all, data.

Rajeswari A.M., CSE, TCE Page 1 of 4


14CS440 / Database Management Systems 2018

Levels of Abstraction
1. Physical level: describes how a record (e.g., customer) is stored.
2. 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;
3. View level: application programs hide details of data types. Views can also
Hide information (such as an employee’s salary) for security purposes.

An architecture for a database system

Rajeswari A.M., CSE, TCE Page 2 of 4


14CS440 / Database Management Systems 2018

Database System Architectute

Rajeswari A.M., CSE, TCE Page 3 of 4


14CS440 / Database Management Systems 2018

Data Models
- Is a collection of tools for describing Data, Data relationships,
Data semantics and Data constraints.
- Provide description of DB design in physical, logical and
view model.
 Relational model
- Record based model.
 Entity- Relationship data model
- Perception of real world object used for DB design.
 Object- based data models
- Object-oriented
- Object-relational
 Semi structured data model
- XML ( Individual data of same type can have different set of
attributes )
 Other older models:
- Network model
- Hierarchical model

**********************

Rajeswari A.M., CSE, TCE Page 4 of 4

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