The Hierarchical Model

Developed in the 1960s to manage large amounts of data for complex projects

Basic logical structure is represented by an upside-down “tree”

Hierarchical database model

In the hierarchical model, data is organized as an inverted tree. Each entity has only one parent but can have several children. At the top of the hierarchy, there is one entity, which is called the root.

An example of the hierarchical model representing a university

3

The Hierarchical Model (continued)

The Hierarchical Model (continued) The hierarchical structure contains

levels, or segments Depicts a set of one-to-many (1:M)

relationships between a parent and its children segments Each parent can have many children each child has only one parent

Hierarchical model

Data are organized as an upside down tree. Each entity has only one parent but can have

several children.

The Hierarchical Model (continued) Disadvantages

Complex to implement Difficult to manage Lacks structural independence Implementation limitations Lack of standards

Network database model

In the network model, the entities are organized in a graph, in which some entities can be accessed through several path

An example of the network model representing a university

The Network Data Model•In this model, data is represented by collections of records and relationships among data are represented by links. Ie., the collection of records which are connected to one another by means of links.

•A record is a collection of fields (attributes), each of which contains only one data value.

•A link is an association between precisely two records.

•The structure of the database is shown as an arbitrary graph in which the records form the nodes and links form the edges.

•There is no concept of a root node.

• The operations on a network database are performed through a data manipulation language for network model.

• The operations that can be performed on a network database include find, insert, delete, modify etc.

• The inserting or removing records include connect, disconnect and reconnect operations.

RELATIONALRELATIONALMODELMODEL

RELATIONALRELATIONALMODELMODEL

Relational model Data are organized in two-dimensional tables

called relations. The tables are related to each other. The most popular model.

The Relational Data Model

•In this model,the data is organized into tables (ie., rows and columns). These tables are called relations.

•A row in a table represents a relationship among a set of values.

Consider a sample database with three tables (relations):Suppliers, Items, Quantities:

  Suppliers (sup-no#,sup-name,status, city)

Items ( item-no#, item-name, price)

Quantities (sup-no#, item-no#, Qty)

Sup-no# Sup-Name Status City

S1

S2

S3

Britannia

New

Cockg

10

30

10

Delhi

Mumbai

Delhi

Suppliers

Item-no# Item-name Price

I1

I2

I3

I4

I5

I6

Milk

Cake

Bread

Biscuit

Ice cream

Jam

15.00

5.00

9.00

14.00

6.00

10.00

Items

Sup-no# Item-no# Qty

S1

S1

S1

S2

S2

S3

I2

I3

I6

I4

I5

I1

10

20

20

20

10

10

Quantities

•Rows of relations are generally referred to as tuples and the columns are usually referred to as attributes.

•No two tuples are identical and their ordering is not important.

•A relationship is represented by combining the primary key of the relations.

•various operations can be performed on relations such as insert new tuples, delete tuples and modify tuples.

•There are several languages for expressing these operations. One such language is relational query language.

Relational model

RDBMS (Relational Database Management System) external view

The data are represented as a set of relations. A relation is a two-dimensional table.

This doesn’t mean that data are stored as tables; the physical storage of the data is independent of the way the data are logically organized.

Relation

Name – each relation in a relational database should have a name that is unique among other relations.

Attribute – each column in a relation. The degree of the relation – the total number of attributes for a

relation.

Tuple – each row in a relation. The cardinality of the relation – the total number of rows in a

relation.

OPERATIONSOPERATIONSONON

RELATIONSRELATIONS

OPERATIONSOPERATIONSONON

RELATIONSRELATIONS

Operations on relations

In a relational database, we can define several operations to create new relations out of the existing ones.

Basic operations: Insert Delete Update Select Project Join Union Intersection Difference

Insert operation

An unary operation. Insert a new tuple into the relation.

Delete operation

An unary operation. Delete a tuple defined by a criterion from the relation.

Update operation

An unary operation. Changes the value of some attributes of a tuple.

Select operation

An unary operation. It is applied to one single relation and creates another

relation. The tuples in the resulting relation are a subset of the

tuples in the original relation. Use some criteria to select

Project operation An unary operation. It is applied to one single relation and creates another

relation. The attributes in the resulting relation are a subset of

the attributes in the original relation.

Join operation A binary operation. Combines two relations based on common attributes.

Union operation

A binary operation. Creates a new relation in which each tuple is either in

the first relation, in the second, or in both. The two relations must have the same attributes.

Intersection operation

A binary operation. Creates a new relation in which each tuple is a

member in both relations. The two relations must have the same attributes.

Difference operation A binary operation. Creates a new relation in which each tuple is in the

first relation but not the second. The two relations must have the same attributes.