1. The transformation of an ER or EER model into a relational model

2. Transforming an ER model into a relational model
ER model - not supported directly by any DBMS
needs to be translated into a model that is supported by DBMSs
transformation / mapping process
non-deterministic
certain ER configurations can be expressed in more than one way in the relational model
certain aspects related to the relational model are not specified in the ER model
transformation guidelines (rules)
some approaches propose two phases
ER model to translatable ER model (this can be optional/implicit)
translatable ER model into relational model

3. ER model  relational model entities
strong entity  base relation
simple, single valued base attributes - ok
composite - flatten
multi-valued - introduce entity and link with 1:M relationship
calculated attributes - eliminate
weak entity  base relation
primary key contains part of the strong entity primary key
foreign key referencing the base relation corresponding to the strong entity
how is the “weak entity” information modelled in the relational model?
cannot have SET NULL or SET DEFAULT

4. ER model  relational model binary relationships
one to one
one partial and one total participation  foreign key from the base relation corresponding to the entity with partial participation to the one with total participation
two partial participations  one foreign key from one base relation to another
two total participations  as above or merge
why would you want to keep them separate?
one to many
FK from the “many entity” relationship to the “one entity” relationship
does it matter whether the “many entity” is weak or strong?

5. ER model  relational model binary relationships
many to many
no attributes
relationship  relation consisting of two foreign keys, one for each relation corresponding to the two entities involved
the two foreign keys  primary key
alternatively, change the ER model
with attributes
transform relationship into entity
implement the two resulting 1:M relationships

6. ER model  relational model binary relationships
Activity: how are the participation constraints represented? e.g.:
Student
Student No No 1
0..1
takes
takes
0..*
1..*
Project
Project
Title
Supervisor
Title
Supervisor

7. ER model  relational model complex relationships
with attributes
transform into entity
no attributes
relationship  relation consisting of foreign keys, one for each relation corresponding to the entities involved
alternatively, transform complex relationship into binary relationships

8. ER model  relational model recursive relationships
introduce new entity
Staff
staff
Staff
staff
manager
manager
0..*
0..1 1 1
natIns
natIns
IsAllocatedTo
HasAllocation
Allocation
0..1
IsManaged
0..*

9. ER model  relational model recursive relationships
Activity: what is the difference between (a) and (b)?
(a)
(b)

10. EER model  relational model
Activity: translate type hierarchies

11. Conclusion conceptual model  logical model
is the resulting logical model the model that is going to be implemented?
logical design  expressing further constraints on data
functional dependencies
multi-valued dependencies
join dependencies
if they are not correctly expressed - the logical model can lead to update anomalies