A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose 2. DBMS
It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
3. Database system
The database and DBMS software together is called as Database system.
4. Advantages of DBMS?
Ø Redundancy is controlled.
Ø Unauthorized access is restricted.
Ø providing multiple user interfaces.
Ø Enforcing integrity constraints.
Ø Providing backup and recovery.
5. Disadvantage in File Processing System
Ø Data redundancy & inconsistency.
Ø Difficult in accessing data.
Ø Data isolation.
Ø Data integrity.
Ø Concurrent access is not possible.
Ø Security Problems.
6.The three levels of data abstraction
Ø Physical level: The lowest level of abstraction describes how data are stored.
Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
Ø View level: The highest level of abstraction describes only part of entire database.
11. Data Independence
Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.
Two types of Data Independence:
Ø Physical Data Independence: Modification in physical level should not affect the logical level. Ø Logical Data Independence: Modification in logical level should affect the view level. NOTE: Logical Data Independence is more difficult to achieve
12. View & How is it related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary. Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
13 Data Model
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
14. E-R model
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
15. Object Oriented model
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
It is a 'thing' in the real world with an independent existence.
17. Entity type
It is a collection (set) of entities that have same attributes.
18. Entity set
It is a collection of all entities of particular entity type in the database.
19. Extension of entity type
The collections of entities of a particular entity type are grouped together into an entity set.
20.Weak Entity set
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
It is a particular property, which describes the entity.
22 Relation Schema & Relation
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of...
Please join StudyMode to read the full document