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Advantages and disadvantages, architectures and data models
Advantages and disadvantages,
architectures and data models
Lecture 3
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Advantages and disadvantages, architectures and data models
Advantages
 redundancies can be reduced
• sometime redundant data is necessary
 inconsistencies can be avoided
 data can be shared
 data independence
• improved maintenance of the IS
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Advantages and disadvantages, architectures and data models
Advantages

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integrity can be maintained
security can be imposed
concurrent access can be achieved
better recovery mechanism
IS’s conflicting requirements can be balanced
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Advantages and disadvantages, architectures and data models
Disadvantages
 complexity
• seem to require more work (skills, time, resources …)
• eventually it pays off
 higher impact of failure
 possibly, reduced local performance
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Advantages and disadvantages, architectures and data models
The client-server architecture
Application x
Application 1
Application 2
Application 3
MACHINE #2
Application y
Application z
MACHINE #n
MACHINE #1
communication network
DBMS (back end server)
server machine
database
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Advantages and disadvantages, architectures and data models
(Totally) Distributed database systems
Client
SERVER
Client
SERVER
Client
SERVER
database 2
database n
database 1
communication network
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Advantages and disadvantages, architectures and data models
Data models
 recall: physical data independence
 how is data described and manipulated at the
conceptual/logical level?
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concepts
operators
grammatical rules
(these apply to any formal language)
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Advantages and disadvantages, architectures and data models
A theoretical model (theory) - Lego
relevant information
about an organisation
(real life system)
(RELATIONL) THEORY
concepts (data type, …)
operators (restrict, …)
rules (syntax)
THEORETICAL MODEL 1
(of the real life system)
THEORETICAL MODEL N
(of the real life system)
operators
rules
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Advantages and disadvantages, architectures and data models
Data models
 the relational model
 the entity relationship (E/R) model
 E/R diagram
 the enhanced E/R model (EE/R)
 the object oriented model
 the object/relational model
 the logic model
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Advantages and disadvantages, architectures and data models
Data modelling and database development
DATA MODELLING THEORY
real life system
abstract data model
part of theory
abstract level
implementation level
implemented (part of) theory
implemented data model
(database system)
DBMS
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Advantages and disadvantages, architectures and data models
Course syllabus - main topics
 generalities
 the relational model
 SQL
 database design / modelling
 data protection
 advanced topics / new trends
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Advantages and disadvantages, architectures and data models
Activity
Have you ever used a theoretical model? Have you ever done
Maths? Have you ever programmed? How is music described?
Can you see any similarities between these disciplines? Can
you infer a model for data modelling based on a theoretical
model you know and the requirements for data modelling?
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