Databases are an integral part of an organisation. To make a good application we should design and implement the database correctly
Database Management Systems
v A database is a collection of logically related information.
v Database Management is the task of maintaining databases so that information is readily available.
v The software required to perform the task of database management is called a Database Management System (DBMS).
Data Models
To create a Database we have two Models
Ø Object-based Logical Model Focuses on describing the data, the Relationship among the data, and any constraints defined
Ø Record-based logical model focuses on describing the data structure and the access techniques in the DBMS
Object-Based Logical Model
Ø Object based Logical Model is based on Entity-Relationship model (ER model)
Entities
Ø Entity is “a thing, which can be easily identified”.
Ø An entity is any object, place, person, or activity about which data is recorded.
Ø In the diagramming technique, entities are named and represented inside a box.
Ø An entity type is a set of things that share common properties:
v STUDENT, COURSE, and GRADE are examples of entity type.
v An entity type is usually in uppercase.
Ø Types of Entities:
v Dependent entity:
ü Is an entity whose existence depends on the existence of another entity and are also called weak entities
v Independent entity:
ü Is an entity which does not depend on any other entity for existence and are also called regular entities
Relationships
Ø It is an association among entities.
v For example, the relationship between students and teacher represents that a teacher teaches several students and a student is taught by several teachers. This relationship could be named TEACH.
Ø Relationships are depicted as a diamond with the name of the relationship type.
Ø A relationship type is an association of entity types (STUDENT-TEACHER).
Ø A relationship can associate an entity with itself. For example, one Teacher in a university may teaches another Teacher.
Ø Multiple relationships can also exist between the same entities.
Types of Relationships
Ø There are three types of relationships:
v One-to-One
v One-to-Many (or Many-to-One)
v Many-to-Many
Ø One-to-One Relationship
EgIn University one Department is headed by on Department head (One to one Relationship)
Ø Many-to-One Relationship
Eg One Student teaches by many teachers.
Ø Many-to-Many Relationship
Eg Many Students have taken admission in many courses.
Record-Based Logical Model
Ø Hierarchical model
v In a hierarchical model, data is represented in the form of a tree.
Ø Network model
v A network model is similar to a hierarchical model in the way that data and the relationships among them are represented in the form of records and links.
Ø Relational model
v In the relational model, the database is structured in fixed-format records of several types.
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