PROTOTYPE DBMS

Topics: Academic degree, Entity-relationship model, Data modeling Pages: 63 (11094 words) Published: April 19, 2015
Week 2 Question 2
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Given the business rule “an employee may have many degrees,” discuss its effect on attributes, entities, and relationships. (Hint: Remember what a multivalued attribute is and how it might be implemented.) Reply Quote Email Author

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1 year ago
Sorayuth Chiewchansuwan
RE: Week 2 Question 2
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An employee may have many degree means that each employee may have more than one degree, Bachelor, Master, and PhD. Also, each degree can be earned by many employees. Therefore the relationship will be M:N relationship. However, the we can use the multivalued attribute to combine all the degrees in to one entity, for instance, we can name the entity as DEGREE and put PhD, Master, and Bachelor in it.  One problem we need to consider is that it will be very difficult to count them as all the information are gathered within the same entity.

Bert
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1 year ago
Ravi Karan Mallarapu
RE: Week 2 Question 2
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"An employee may have many degrees". 
Here, employee ID alredy exists and is a field/attribute in itself. Hobbies requires a new field/attribute and comes under the entity of student details.  The relationship is 1:M and the model is based on how you build the table. We can create a new table with fields for employee ID and every possible degrees. Here, the primary key of the employeeID becomes foriegn key in the new relation table. But, this model leads many null values which can be still operated. If we use only a field for "hobbies" we need to assign the text field to contain  more than one value. This is called as multivalued attribute. Here, a new schema is created with clear definitions of attributes about what type of attributes can be present and the number of instances of those values ie 1 or more. But still each value in a given value set must be unique without repetitions within the same location.  The new schema contains a primary key, which is a combination of the emloyeeID (foriegn key and unique identification value) and degree(a unique descriptive attribute). New pk pair scheme of employeeID and individual degrees helps in identifying which degree belongs to which employee and which employee has what degrees.

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1 year ago
Ravi Karan Mallarapu
RE: Week 2 Question 2
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Sorry a typing mistake. It is "degress" in place of "hobbies" Reply Quote Delete
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1 year ago
John Harrington
RE: Week 2 Question 2
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The relationship between Employee and degree is a M:N relationship. An employee could have one or more degrees and different types of degrees such as bachelors, masters, Ph.D, and maybe a JD could be assigned to one or more employees.

 It would be best to create an entity for Degree. The primary key from Employee should be used as a foreign key in Degree. Degree should have a key called DE_TYPE that could hold a degree type for each degree that the employee has earned. The Degree table could also be expanded to hold information about where and when a degree was earned. Reply Quote Email Author

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1 year ago
Ravi Karan Mallarapu
RE: Week 2 Question 2
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Hi John,
Your example of degrees with the new attributes of where and when a degree was earned  seem to form an interesting combination of multivalued attribute and weak entities. The dergrees is of course a multivalued attribute.

The attributes "when passed" and "where studied" form weak entities which do not come...
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