Data Models, Schemas & Instances
Transcript of Data Models, Schemas & Instances
Data Models, Schemas & Data Models, Schemas & InstancesInstancesAndAndDatabase LanguagesDatabase Languages
Data ModelData ModelA collection of concepts that can be used to
describe the structure of a databaseData model is a collection of conceptual(logical)
tools for describing data, relationship etc.provides the necessary means to achieve data
abstractionBy structure of a database, we mean the data types,
relationships, and constraints that should hold for the data
04/07/23 Database Management System 2
Categories of Data ModelsCategories of Data Models
High level or Logical (Conceptual)Data Model – provide concepts that are close to the way many users perceive data
Low level or Physical Data Model - provide concepts that describe the details of how data is stored in a computer
Representational Data Model - provide concepts that may be understood by end users but that are not too far removed from the way data is organized within the computer.
04/07/23 Database Management System 3
CONTINUEDCONTINUED……Physical data models defines record structure, file
structure etc.Logical data models use concepts such as entities,
attributes & relationships Entity – represents a real world object or a concept
Ex: employee, student, projectAttribute - represents some property of interest that
further describes an entity Ex: Employee's name or salary.
04/07/23 Database Management System 4
TYPES OF DATA MODELSTYPES OF DATA MODELSLogical Data Model
Entity – Relationship Model (ER model) Object – Oriented Model
Representational or Implementation Data Model
Relational Model Network Model Hierarchical Model
04/07/23 Database Management System 5
ENTITY - RELATIONSHIP (ER) ENTITY - RELATIONSHIP (ER) MODELMODEL
It is based on a perception of a real world that consists of a collection of basic objects, called entities and the relationships among these objects.
The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram
04/07/23 Database Management System 6
EXAMPLE ER DIAGRAM FOR EXAMPLE ER DIAGRAM FOR COMPANY DATABASECOMPANY DATABASE
04/07/23 Database Management System 7
Employee Department
Age
Salary
Ssn
Emp_Name
Dept_Location
Dept_Name
Dept_Number
Dept_Number
Mgr_Ssn
Works in
RELATIONAL MODELRELATIONAL MODELUses a collection of tables to represent both data
and the relationships among those dataEach table has multiple columns, and each
column has a unique nameIn the formal relational model terminology, a
row is called a tuple, a column header is called an attribute, and the table is called a relation
In Relational model data is organized in the form of tables .
04/07/23 Database Management System 8
It uses a collection of tables to represent both data and the relationships among those data.
The advantage of this model is that it offers flexibility. This is the most popular method
04/07/23 Database Management System 9
Cust-name
Social security
Cust-street
Cust-city
A/c no: Balance amt
johnson 1 xxx yyy A-101 500
smith 2 yyy xxx A-215 200
hayes 3 aaa bbb A-102 100
turler 4 bbb aaa A-201 100
jones 5 ccc ddd A-217 120
lincy 6 ddd ccc A-222 200
smith 2 yyy xxx A-201 --
johnson 1 xxx yyy A-201 --
Here balance is not given in the first table. We have to represent the relationship b/w account no: and balance is shown in the next table
04/07/23 Database Management System 10
Cust-name
Social security
Cust-street
Cust-city A/c no:
johnson 1 xxx yyy A-101
smith 2 yyy xxx A-215
hayes 3 aaa bbb A-102
turler 4 bbb aaa A-201
jones 5 ccc ddd A-217
lincy 6 ddd ccc A-222
smith 2 yyy xxx A-201
johnson 1 xxx yyy A-201
a/c no Balance amt
A-101 500
A-215 200
A-102 100
A-201 100
A-217 120
A-222 200
04/07/23 Database Management System 11
Network modelNetwork model
Here data is organized as a collection of records and the relationships among data are represented by links.
It looks like an arbitrary graph.The collection of records connected to one
another by means of links, where link is an association between 2 records.
The operations on the n/w model are find, insert, delete, modify etc.
04/07/23 Database Management System 12
johnson
1 ---
04/07/23 Database Management System 13
A-201 100
hayes 3 ---
turler 4 ---
lincy 6 ---
smith 2 ---
jones 5 --- A-217 120
A-222 200
A-102 100
A-215 200
A-101 500
Hierarchical modelHierarchical modelHere data is represented by collection of records
and relationships among data by linksIt is similar to network modelThe only difference is that it takes the structure
of a tree
04/07/23 Database Management System 14
johnson
1 ---
04/07/23 Database Management System 15
A-201
100
hayes
3 --- turler
4 ---
lincy
6 ---
smith
2 ---
jones
5 ---
A-217 120
A-222
200
A-102
100A-215 200
A-101
500
root
A-201
100
A-201
100
DATABASE SCHEMADATABASE SCHEMAThe description of a database is called the database
schema It is the complete structure of database.Subschema is a part of the database pertaining to the
user’s need. To create a schema , the syntax is :
CREATE SCHEMA schemaname [AUTHORIZATION username] [schema element[…]]
Where schemaname is the name of the schema that is to be created. Authorization class is used for all created objects that can be later owned by the user.
04/07/23 Database Management System 16
SCHEMA DIAGRAM FOR A SCHEMA DIAGRAM FOR A COMPANYCOMPANY DATABASE DATABASE
04/07/23 Database Management System 17
Ssn Emp_Name Age Mgr_Ssn Dept_NumberSalary
Employee
Dept_Number Dept_Name Dept_Location
Department
A displayed schema is called a schema diagram
INSTANCESINSTANCESThe data in the database at a particular moment
in time is called a database state or snapshotIt is also called the current set of occurrences
or instances in the database
04/07/23 Database Management System 18
AN INSTANCE FOR THE AN INSTANCE FOR THE EMPLOYEEEMPLOYEE TABLETABLE
04/07/23 Database Management System 19
Ssn Emp_Name Age Salary Mgr_Ssn Dept_Number
101 Mathew 32 50000 NULL 1
102 David 27 37000 101 1
103 Mary 23 20000 102 2
104 John 26 30000 101 2
105 Catherine 23 22000 104 2
DATABASE LANGUAGESDATABASE LANGUAGESData Definition Language (DDL) – to specify
the database schemaData Manipulation Language (DML) - to
express database queries and updatesDDL and DML are not two separate languages.
Instead they simply form parts of a single database language, such as the widely used SQL (Structured Query Language)
04/07/23 Database Management System 20