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Database Management System

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DBMS: The database management system, is a generalized software system for manipulating databases. It is basically a computerized record-keeping software system; which stores information and allows users to add, delete, change, retrieve and update that information on demand.

ADVANTAGE OF DBMS ARE

1. Minimal data redundancy
2. Program-data independence
3. Efficient data access
4. Improved data sharing
5. Improved data consistency
6. Improved data integrity
7. Improved security
8. Increased productivity of application development
9. Enforcement of standards
10. Economy of scale
11. Balance of conflicting requirement
12. Improved data accessibility and responsiveness

DISADVANTAGES OF DBMS ARE

1. Increased complexity
2. Required of new specialized skilled manpower
3. The large size of DBMS
4. Increased installation and management costs.
5. Need for explicit backup and recovery


  DATA MODELS:  Data model is a mechanism that provides an abstraction for database applications. Data modeling is used to represent entities of interest and their relationship in the database.


TYPES OF DATABASE MODELS ARE:

 1. Record based- further divided into three main parts

     a. Hierarchical data model
     b. Network data model
     c. Relational data model

 2. Object-based data models- further divided into

     a. ER model
     b. Semantic
     c. Functional
     d. Object oriented

 3. Physical data models-further divided into

     a. Unifying model
    b. Frame memory


 HIERARCHICAL DATA MODEL: 

1. Are represented by an upside-down tree. The user perceives the hierarchical database as a           hierarchy of segments.  A segment is equivalent to a file system record type. The relationship between and record forms a hierarchy.

2. A tree may be defined as a set of nodes such that there is one specially designed node called the root node.

Advantage of hierarchical data model:

 a. Simplicity
b. Data sharing: all data hold in a common database model, data sharing becomes practical.
c. Data independence
d. Data integrity

The disadvantage of the hierarchical data model:

 a. Implementation complexity
b. Inflexibility
c. Lack of structural independence
d. No standard
e. Extensive programming efforts


NETWORK DATA MODEL

1. It is a flexible approach to representing objects and their relationships.

2. A unique feature of this data model is its schema, which is viewed as a graph where relationship types are arcs and object types are nodes.

3. In-network data model technology is a relationship is called a set in which each set is composed of at least two record types. 1st record is called owner record type and 2nd called member record types. the connection between the owner and member record is identified by a link to which database designer assigns a set_name. This set name is used to retrieve and manipulate data.

4. In network data model, a member can appear in more than one set and thus may have several owners and therefore it facilitates many (m:m) relationships between the owner and the member.


 RELATIONAL DATA MODEL 

Relational database management originates from the mathematical concept of relation and set theory, it was 1st proposed as an approach to data modeling by Edgar F. Codd of IBM research in 1970. The relational model uses the concept of a mathematical relation in the form of a table of values and its building block.


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