Advantages and disadvantages, architectures and data models Lecture 3

Advantages redundancies can be reduced inconsistencies can be avoided sometime redundant data is necessary inconsistencies can be avoided data can be shared data independence improved maintenance of the IS

Advantages integrity can be maintained security can be imposed concurrent access can be achieved better recovery mechanism IS’s conflicting requirements can be balanced

Disadvantages complexity higher impact of failure seem to require more work (skills, time, resources …) eventually it pays off higher impact of failure possibly, reduced local performance

The client-server architecture

(Totally) Distributed database systems

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)

A theoretical model (theory) - Lego

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

Data modelling and database development

Course syllabus - main topics generalities the relational model SQL database design / modelling data protection advanced topics / new trends

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?