Question

Part 1 - List at least four basic rules for identifying primary keys in a relational database. Mention how you would go about identifying the foreign keys in your design. Briefly discuss foreign key ownership and how to indicate a foreign key in your relational database model.

Part 2 - Describe at least two examples of common errors in entity relationship modeling. If possible, provide a graphical illustration of the problems and solutions. List some questions the designer should consider before designing the models so that these errors can be avoided.

Answer 1

Answer)

1) Ways to identify the primary keys in the relational database is with the following ;

a) The primary key would contain the unique values for every row of a data

b) It should also not have null values

c) While a primary key would have multiple columns the data from every column would be used for determining the row uniquely

d) For primary key, the data must refer to the rows and not the columns.

For the foreign key:

a) One or more columns in the table refer to the primary keys in another table

b) There is no special configuration or table or code or table definition for a foreign key

When considering the foreign key ownership, it is considered as the key attributes not being considered to be owned by the entities where it would migrate as they are considered as the reflection of the attributes in the concerned parent entities, hence every attribute in the entity would either be owned by the entities or the foreign key.

For indicating the foreign key in the relational database model, it is considered as the field or the collection of the field in a certain table which can help in identifying the row of the other table or the same table as well.

Answer Part 2)

Some of the errors associated with the entity-relationship modeling are that it might have incomplete data model errors or the MIS model problem domain etc.

The incomplete data happens when system analyst gets to task for building the computer-based information system that is having a limited scope. If this can be prevented then this error can also be prevented.

The error of mismodel happens while depicting the attribute which has the single value or multivalued or for any single entity which would include attributes that would have been assigned to 2 different entities or the relationship degrees or by mismodeling the connectivity. If this can be prevented then the errors can be avoided.

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