Database and Database Design: Lecture Two - ANSI-SPARC Architecture and Data Independence, Lecture notes of Introduction to Database Management Systems

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MODELS OF

DATABASE AND

DATABASE DESIGN

LECTURE TWO

OBJECTIVES

By the end of this lecture students should

be able to (I ) describe the the 3 levels of

abstraction that were identified by the

American National Standards Institute

Special Planning and Requirements

Committee (ANSI-SPARC) and

(ii) define the term data independence

and identify the 2 types of data

independence that exist in relation to the

ANSI-SPARC Architecture.

The three ANSI/SPARC levels of

abstraction

physical storage Internal level Conceptual level View_1 View_2 View_3 View_n External Level

EXTERNAL LEVEL

• (^) It represents the user’s view of the database
• (^) It describes that part of the database that is

relevant to a particular user

• (^) It excludes irrelevant data as well as data which the

user is not authorised to access.

• (^) Views may include derived or calculated data

INTERNAL LEVEL

• (^) The internal level involves how the database is physically represented on the computer system. It describes how the data is actually stored in the database and on the computer hardware.
• (^) Is concerned with: allocating storage space for data and indexes; describing the forms that records will take when stored; record placement; data compression and encryption techniques

Difference between External, Conceptual and Internal Level Accounts Office View Students Registration Office View RegNo, Name, Fees Paid RegNo, Name, Programme, Level RegNo, Name, Fees Paid, Programme, Level Create Table Students ( RegNo varchar(15) UNIQUE NOT NULL, Name varchar (20), Fees Paid currency, Programme varchar (20) UNIQUE, Level int, Primary Key (RegNo) )

Data independence

• Data Independence refers to the ability to change the schema at a lower level and the changes do not affect the schema at a higher level; of 2 types:
• Physical Data Independence
  • This is the immunity of the conceptual schema to changes at the internal level
• Logical Data Independence
  • This is the immunity of the external schema to changes at the conceptual level

Representation of data

independence

physical storage Internal level Conceptual level View_1 View_2 View_3 View_n Logical D Independ Physical Independ