Record-Based Logical Model

Record-Based Logical Model

Now that you are familiar with the ER model, which is an example of an object- based logical model, we will look at
other data models. The three types of record- based logical models are:

Hierarchical model : 

In this model, data is represented in the form of a tree, and relationships between the data are represented by links.

Network model : 

In this model, the data and relationships among them are represented in the form of records and links. It is similar to a hierarchical model. However, records in a database are represented graphically.

Relational model :

 In this model, the table in a database has a fixed length record with fixed number of attributes or fields. Of these three models, the relational model is the most popular

Subtypes and Supertypes

Subtypes and Supertypes

 A subtype is a subset of another entity.

For example, 

consider the entity COURSE. There are two types of COURSEs, semester and standalone. The entity, COURSE is the supertype, and SEMESTER and STANDALONE are the subtypes. There are some attributes that are common to both the subtypes, for example: “course code”, “name”, and “content”. STANDALONE courses have some attributes such as “duration” that do not belong to the subtype, SEMESTER. The SEMESTER subtype has some attributes such as “semester_no” that do not belong to the STANDALONE subtype

Types of Relationships

Types of Relationships 

There are the following types of relationships:

1. One- to- One
2. One- to- Many (or Many-to-One)
3. Many-to-Many 

Object-Based Logical Model

Object- Based Logical Model

There are various object-based logical models, such as
Entity-Relationship (ER) model, object- oriented model, and binary model. The most widely used is the ER model. It is accepted as an ideal data model for the database design. Peter Chen introduced this model in 1976, and since then several people have added value to it.

The ER Model

 The ER model views the real world as a collection of objects or entities and the relationship among them. Chen introduced not only the ER model, but also a corresponding diagramming technique.

Entities 

Chen defined an entity as “a thing, which can be easily identified”. An entity is any object, place, person, or activity about which data is recorded. An entity can be categorized as entity type and entity instance. An entity type is a set of things that share common properties.

Relationships

 Chen defined a relationship as “an association among entities”. For example, there is a relationship between students and teachers. This relationship represents the fact that a teacher teaches several students and a student is taught by several teachers. This relationship could be named TEACH. 

RDBMS INTO

A Database Management System (DBMS) is software used to store and manage data. A DBMS stores data in databases and uses data models to show the various ways of managing data. A Relational Database Management System (RDBMS) is an advanced version of a DBMS that also defines the relationship between the various data values. This feature helps in managing and using data more efficiently than DBMS. This chapter introduces DBMS and describes the various types of data models. It explains the most widely used entity relationship model and discusses the various types of relationships among the entities. In addition, the chapter describes the various ways of accessing data by using relational operators and joins.

Database Management System

A database is a collection of logically related data. Data means known facts, which are meaningful and can be recorded. For example, names, telephone numbers, and addresses.

    DATA MODEL

A data model is a description of the data in a database. In addition, the data model describes the relationship among data, and any constraints that have to be defined on the
data. Data models can broadly be classified into the following categories:

Object- based logical model : Focuses on describing the data, the relationship among the data, and any constraints defined.

 Record- based logical model : Focuses on specifying the logical structuring of the database in the form of tables.