1. Advantages and disadvantages, architectures and data models
Lecture 3

2. 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

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

4. 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

5. The client-server architecture

6. (Totally) Distributed database systems

7. 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)

8. A theoretical model (theory) - Lego

9. 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

10. Data modelling and database development

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

12. 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?