CHAPTER 1:
Database system have taken us from a paradigm of data processing in which each application defined and maintained its own data to one in which the data is defined and administered centrally.
Database is a collection of related data. Database characteristics are persistent, shared, and interrelated.
Database system is a system with a database, a DBMS and a full description of the structure and constraints of the data stored in the database.
Database management system (DBMS) is a software system that enables users to define create, and maintain the database and providers control access to this database.
Functions of Database management system:
- Data storage, retrieval and update.
- Data dictionary management.
- Transaction support.
- Multiuser access control.
- Backup and recovery management.
- Security management.
- Support for data communication
- Data integrity management.
- Services to promote data independence.
- Utility services.
The advantages of Database management system:
§ Control of data redundancy
§ Data consistency
§ Access versatility
§ Program and file independence
§ File consolidation.
§ Improved security
§ Improved data integrity
Three schemes supported by client server architecture are:
Ø Client, server and database on the same computer.
Ø Multiple clients and one server on different computers.
Ø Multiple servers and database on different computers.
Two types of Data Independence:
v Logical data independence
Protection from changes in logical structure of data.
v Physical data independence
Protection from changes in physical structure of data.
Three levels of database system architecture
ü External level: users’ view of the database
ü Conceptual level: Community view of the database
ü Internal level: physical representation of the database on the computer
The 6 components of DBMS
- Query processor
- Database manager
- File manager
- Data manipulation language processor
- Data definition language compiler
- Dictionary manager
CHAPTER 2:
Specialization: A specialized kind of entity set may be derived from a given entity set.
Generalization: Several entity sets can be abstracted by a more general entity set.
Categorization is the modelling of a single subclass with a relationship that involves more than one distinct superclass.
The relational data model has one data structure, the relation. The relation is a restricted table.
Relations are defined in terms of attributes, tuples, primary keys, foreign keys and domains.
A special character exists in relational systems for representing incomplete or missing information.-null
The model also has two inherent integrity rules: entity and referential integrity and enterprise constraints.
Normalization is a process for assigning attributes into table and reduces data redundancy and helps eliminate the data anomalies that associated with poor database design (unnormalized).
Four levels of normalization:
- 1NF –a relation where the intersection of each row and column contains no repeating values. (only one values)
- 2NF –a relation that is in 1NF and every non-key primary key attribute is fully functionally dependent on primary key.
- 3NF –a relational based on the concept of transitive dependency.
- BCNF –a relational based on the concept of the determinant.
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