lecture3

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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