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
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?
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 9
Advantages and disadvantages, architectures and data models
Data modelling and database development DATA MODELLING THEORY real life system
part of theory
abstract data model
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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