weekly reflection 1

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

1. Query  processor
2. Database manager
3. File manager
4. Data manipulation language processor
5. Data definition language compiler
6. 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.