Guide IV
Part 2 The Relational Model and Languages
Chapter 4 The Relational Model
4.1 Describe the main characteristics of the Relational Data Model, including the properties of
relations and the rules for relational integrity.
Relational
set of tables (as perceived by users)
rows/columns
variety of possible storage structures
no repeating groups
Entity Integrity: No attribute participating in the PK of a base relation is allowed to accept null
values.
4.2 The Relational and CODASYL models are examples of two different approaches by which a
Database Management System will be classified. Make a detailed comparison of each of these
models, indicating clearly the relative advantages and disadvantages of each.
CODASYL
records in chains/rings
Relational
set of tables (as perceived by users)
CODASYL Data Model Advantages
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longevity and availability of DBMSs for this model
CODASYL Data Model Disadvantages
Relational Data Model Advantages
simplicity
4.3 Describe the difference between a base relation and a view and discuss the main benefits of
using views in a relational database.
A base relation is a named relation, corresponding to an entity in the conceptual schema, whose
tuples are physically stored in the database. A view can be constructed by performing operations
The main benefits of views includes:
It provides a powerful and flexible security mechanism by hiding parts of the database from
4.4 ata
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independence?