For the student dorm set of questions from lecture 17, three questions were asked create an IR ID The first question, Are you satisfied? No anomalies exist in your ID second question. identify any functional dependencies. Third question. The answers are now shown. There were four questions for the CRM set from lecture 17.

One, create an RD two, are you satisfied with no anomalies? Three, identify any functional dependencies for what is the next step after the end? The answers are now displayed. too subtle for often asked questions are no values and mandatory relationships. And no value states that the value in a cell does not exist. For example, if you were collecting information above the age of a customer or participant, would they willingly give you the number?

The problem would know values is that they are ambiguous. Does it mean the person doesn't know or possibly is not willing or worse may give you an erroneous number. We can eliminate the problem by requiring that the value be provided, but DBMS do allow for inputting a null value in a column with a no declaration. A mandatory relationship argument follows. In a student gone example, a student may reside in at most one dorm, but possibly may not live on campus. Put simply a student may not necessarily be found living in a dorm.

In the language of entities we say the type of participation between student in the dorm entity is optional. If the minimum cardinality is one, the entity relationship is mandatory.