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Database Design Relationship Explanation

   

Added on  2019-09-16

2 Pages505 Words176 Views
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1.Is the relation between Patient_inforamtion and Signs classes, is a One-to-many and mandatory. Because the patient has zero or more signs and also one signs belong to zero or multiple patients. My question, is the above relationship correct and explain what we want?Answer: a person will only be a patient if he or she has one or more signs. If they do not have any signs, why would their information be registered as a patient. Rest I have corrected. You are right that a sign may belong to zero or more patients. 2.Can you please explain, why are there a composition relationship between Signs and Sign_Recommendation classes? Answer: this is a composition because sign_recomendation class cannot exist independently.Since you have created both recommendation_id and sign _id as a primary key together hence they cannot hold null values. If they would have been just foreign keys, or signs_recommendation table would not have been there, then we would have created an aggregation or association relationship.3.Can you please explain, why are there a composition relationship between Recommendationand Sign_Recommendation classes? Answer: this is a composition because sign_recomendation class cannot exist independently.Since you have created both recommendation_id and sign _id as a primary key together hence they cannot hold null values. If they would have been just foreign keys, or signs_recommendation table would not have been there, then we would have created an aggregation or association relationship.4.Why the black diamond to (or next to) Signs and Recommendation classes?Answer: diamond is black because of composition relationship. They both are container/ composite classes. Please check your notes5.Can you please explain the reason for choosing the relation between the Sign_Recommendation and Recommendation classes?Answer: due to dependency between them. Since signs are there hence recommendations are there. But the same recommendation can be used for one or more signs. You can say that I have assumed that each sign exists in the database must have a recommendation for it. And each sign may have one or more recommendation or each recommendation can be associated with one or more signs.6.Can you please explain the reason for choosing the relation between the Sign_Recommendation and Signs classes?Answer: same as 5. 7.What the target of Main window? Does the Main window class or not?
Database Design Relationship Explanation_1

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