Author Question: To build an information system, which one do you need to identify first classes or objects? What ... (Read 25 times)

khang · **on:** Jul 7, 2018

To build an information system, which one do you need to identify first classes or objects?

What will be an ideal response?

Question 2

Explain foreign keys are they necessary?

What will be an ideal response?

Melissahxx · **Reply #1 on:** Jul 7, 2018

Answer to Question 1

The process of classification that is, definition of classes starts with a concept: a general idea that is shaped into a distinct class through a mental and semantic process of generalization. In other words, the concept always precedes classification, regardless of whether existing objects give rise to a class or the objects are created from a class.

Answer to Question 2

The relationship between entities in different tables is established through foreign keys. The foreign key is an attribute in one table, the value of which must match the value of a primary or an alternate key in another table. Unlike primary keys, foreign keys are not required and do not, necessarily, identify a row uniquely. Like primary keys, a foreign key can be composite, consisting of more than one attribute.