Database

1.  The Three-level Architecture
I. External model
II. Logical or conceptual model
III. Internal or physical model
Logical Data Models
I. Semantic data model
II. Record based model
DATABASE ARCHITECTURE

2.  THE THREE-LEVEL
ARCHITECTURE
 External model
 Logical Or Conceptual Model
 Internal Or Physical Model

3. THE THREE-LEVEL
ARCHITECTURE

4.  EXTERNAL LEVEL
• The external level interacts directly with the user (end users or application programs). It
changes the data coming from the conceptual level to a format and view that is familiar to
the users.
• Consists of many user models or views
• Has external records - records seen by users
• May include calculated or virtual data
• Devide in external schemas (sub-schemas)
• Used to create user interface

5.  LOGICAL OR CONCEPTUAL MODEL
The conceptual level defines the logical view of the data.
• All entities, attributes, relationships represented
• Includes all record types, data item types, relationships, semantic information, security
and integrity information
• Described in logical schema

6.  INTERNAL LEVEL
• The internal level determines where data is actually stored on the storage devices.
• The DBMS and Operating System View
• Physical implementation level
• Includes data structures, file organizations used by DBMS
• Depends on what DBMS is used

7. WHAT IS DATA INDEPENDENCE
•Techniques that allow data to be changed without
affecting the applications that process it.

8. Slide 2- 8
TYPES OF DATA INDEPENDENCE
• Logical Data Independence:
• The capacity to change the conceptual schema without having to change the external
schemas and their associated application programs.
• Physical Data Independence:
• The capacity to change the internal schema without having to change the conceptual
schema.
• For example, the internal schema may be changed when certain file structures are
reorganized or new indexes are created to improve database performance

10. ¤ In this model database is structured in fixed-format
records of several types.
¤ They allow the designer to develop and specify the
logical structure and provide some options for
implementation of the design
¤ It describes the data at the conceptual and view levels
both.
¤ Specify overall logical structure of the database

11. I. Hierarchical Model
II. Network Model
III. Relational Model

13. ¤ Oldest
¤ Like a structure of a tree
¤ Branches represent fields
¤ Nodes represent record
¤ Structure contains levels, or segments.
¤ Higher layer is perceived as the parent of the segment
directly beneath it, which is called the child

14. S1001 Ali Ahmad Computer
Science
60
Csc01A Intro to Algo Talha TuF10 N45
S1002 Kamal Khan Computer
Science
60
S1008 Noman Ch Computer
Science
60

16. ¤ Like hierarchical model
¤ But may have many to many relation
¤ It allows a record to have more than one parent
¤ Replaces the hierarchical tree with a graph

17. S1001 Ali Ahmad Computer
Science
60
Csc01A Intro to
Algo
Talha TuF10 N45
S1002 Kamal Khan Computer
Science
60
S1008 Noman Ch Computer
Science
60
Mth01A Calculus I Mutiullah MW9 R25

18. :- A student taking two classes
:- A teacher teaches different classes
:- An employee works for two departments

20. ¤ Proposed by E.F. Codd
¤ Uses relations
¤ Contains tables
¤ Tables represent relationships
¤ Columns represent attributes
¤ It’s better than others

21. STDID STDNAME MAJOR CREDITS
S1001 Ali Ahmad Computer Science 60
S1002 Kamal Khan Math 40
S1003 Shoaib Mansoor Computer Science 60
C_ID CNAME PROF SCHED ROOM
Mth01A Calculus I Mutiullah MW9 R25
Csc01A Intro to Algo Talha TuF10 N45
Csc01B Programming I Imran TuThF9 N40
Student - Table
Enrollment - Table
Class - Table
C_ID STDID Grade
Csc01A S1001 B+
Csc01B S1001 A
Mth01A S1002 B
Csc01A S1002 B