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Generalisation and composition relationships logical modelling 

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Generalisation and composition relationships logical modelling 

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Dear Peter,

Is it true that for generalisation and composition relationships these can be modelled as one-to-one relationships? Will they always have 1..1? Also, do we always know the cardinality when reading from the other direction, so for specialisation and aggregation relationships?

Thank you

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Dear Peter,

Could you explain please how we logically model an ER diagram where there is only one entity type which has a relationship with itself.

This was the correct answer in the quiz:

CREATE TABLE DOG_WALKER (DOGWALKER_ID, FIRST_NAME, SURNAME)

PRIMARY KEY (DOGWALKER_ID)

CREATE TABLE FRIENDS (DOGWALKER_1_ID, DOGWALKER_2_ID)

PRIMARY KEY (DOGWALKER_1_ID, DOGWALKER_2_ID)

FOREIGN_KEY  DOGWALKER_1_ID REFERENCES DOG_WALKER(DOGWALKER_ID)

FOREIGN_KEY  DOGWALKER_2_ID REFERENCES DOG_WALKER(DOGWALKER_ID

I don't understand why and how we would split DOGWALKER_ID into 1 and 2?

Thank you

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Peter, for w8's logical design, why do we need to create an extra APPOINTMENT table rather than adding a foreign key to the PATIENT table? Many thanks.

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Hi Peter, could you let us know when's your office/consultation hours? If I remember correct, we are not required to make booking for that right? Thanks.

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Dear Dr Peter, I would like to ask you about the quesition in 'Logical Design 2 University DB Quiz'.

at the first two table, why name use 'constraint name unique not null', why it not in primary key?

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Dear Dr Peter, I would like to ask you about the use of "UNIQUE" in logical model.

From my understanding through the lecture and slides, "UNIQUE" is specified when a Child occurrence is associated with just one Parent. Does it indicate that Child and Parent have one to one relationship when both of their cardinalities are 1 regardless of optionalties (i.e., 0..1, 1..1)? If not, can you give me further details when to add "UNIQUE" in logical model?

I'm reviewing the slides with four examples above, but a bit confused about it. I'd appreciate your help. Thank you.

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Sometimes the cardinality next to the child entity (ROOM in this EER) is missing. I am confused.