Class 1 | Week 4 | DAT602

This week, Todd is transitioning from conceptual modeling into logical modeling, this lesson in particular is focusing on transitioning our conceptual models into logical models.

We have been supplied with a workbook to follow along with as he explains various concepts to us, having some written work to reference to is sure a welcome addition.


Todd is explaining how to resolve our preexisting relationships within our ERD models into the correct format for a logical model, different types of relationships require different methods. This is the first step in building & also validating out logical data models.

The next step is validating relations using normalization which he has stated that he is not going to go into depth on until next Fridays lecture.



Class Notes

Logical Database Design

One to Many relationship

The primary key from the "one" side of the relationship is place sin the "many" relations as a foreign key.

One to One relationship

The foreign key may be placed in either relationship. That is, the primary key of relation A may be placed in relation B as a foreign key, or the primary key of B may be places in relation A as a foreign key. The relational model does not care in which direction you place the foreign key - consider the context of the problem.

Many to Many relationship

A many to many must be resolved with an associative entity/relations or more commonly known in our classes as a joining table, this contains the keys from each relationship as foreign keys. Together, the foreign keys make up the primary key. This relation exist purely to resolve the issue of representing multi-dimensional data in two dimensional formant  and is not necessarily required in other database models (e.g. an object oriented database.

Relationships with attributes

As there is no such thing as a relationship in the relational model (only PK-FK links), relationships with attributes cannot exist To resolve this, a new relation must be created  The PK-FK links will be the same as for an associative relation (Above) but will also include the attributes that were previously linked to the relationship.

Superclass/subclass relationships

Generally there are three different options you can adopt for converting the super type and subtypes into relationship:

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