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Question:Hello, I want to revise my assignment to meet the teacher's requirement. Please see the assignment attached.
Below is the teachers comment.
Feedback to Learner
2/28/17 8:31 AM(a) okay
(b) The diagram you show is incomplete because it does not list the verb on each relationship line. The reader has to guess at the writer's intended meaning.
The change you propose destroys current way of working of the business. So, it is unacceptable. You lost which building each apartment is in. You lost that the renters must sign a contract to rent an apartment. You lost that furniture is part of the rental contract agreement.
Please review carefully the discussion on Redundancy in the Discussion Board.
(c) You have a reasonable idea of the business situation, but you did not say what part of the given E-R model enforces that situation. What in the model requires an apartment to be deleted?
(d) None of your proposed key will work. RenterID cannot be in the key because of symbol A. Since there can be many renters on a single contract, we do not know which one to use n the key. Not unique enough.
You still need to give 3 good candidate keys.
(e) Your statement is only true if the relationships around Renter support it. What is the symbols on the relationship lines apply to prospective renters? What is the symbols on the relationship lines apply to former renters?
(f) You came up with 2 of the 3. You forgot that the rental contract will also have an identifier.
(g) Your answer to (g) is wrong. We must NOT remove the includes reln (EFGH) between Furniture and Rental Contract. Given that, what is the answer on adding a proposed "used by" reln?
(h) No, the apartment WILL be rented. It will be rented by the person who happens also to own the building. There will be a rental contract for that person.
(i) Your answer is inconsistent. You said that there need to be four instances of rental contract. But you said that A means the four students can sign one contract. Which is your answer?
(j) The answer about furniture is wrong. Look at the question again and carefully review all relationships in the E-R model.
Together-While-Still Apartments Inc. (TWSA) manages the rental of furnished apartments and
lofts using a database whose Logical Data Model is shown here. Answer the questions below
based this model only (i.e. "Discover, Don't Invent") A yes/no answer is not sufficient. You must
cite what specific part of the data model provides the answer. The connectivity symbols are
labeled with letters to make it easy to give short, specific, complete answers. A letter (such as C
or R) is sufficient to identify a minimum or maximum symbol in your answer. Do not “overanswer” – if H alone is the right answer, do not say “G and H” or “E,F,G,H” (both wrong).
Together-While-Still Apartments Inc. (TWSA) ERD: (a) Can new furniture be recorded as soon as it is purchased? How do you know?
New furniture can be added according to this database design. The relation (symbol F)
between Furniture and Rental Contract shows that a furniture can has zero or more rental
contact. The symbol S shows that a furniture can in use at zero or multiple buildings.
(b) What part of the model is redundant? How would you change the model to eliminate
the redundancy? Why won't users lose information if you make this change? If a renter has signed more than one rental contracts but rent only one apartment so this data
storage cause of redundancy. Relation D, and I are causes of redundancy. So I have created a
separate relationship between renter and Apartment.
Relation E, H cause of redundancy. To remove this, I have created separate relation between
Renter and Furniture. I have created a new entity “RenterFurniture”. A renter can rent zero or
more renter furniture.
c) Under what conditions will an apartment be deleted from the database? How do
you know?
If owner of an apartment arranges another agency to manage apartment rental details,
then TWSA agency will remove this apartment details from the database.
d) Suggest 3 good potential identifiers (candidate keys) for the Rental Contract
entity. (3 different alternatives, not one concatenation.)
1. Primary key ( renterID, apartmentID) renterContractID will be unique
2. Primary key ( renterID, renterContractID)
3. Primary key ( renterID,furnitureID) renterContractID will be unique e) Can TWSA use this database to track prospective new renters or former renters
who might rent from them again? How do you know?
yes, TWSA use this database to track new renters and old renter’s details. When details
are stored into database, this will remain in database until this data is not deleted from the
database according to requirement. So I can easily track needed information from the
database according to our requirements. For example, if renter Id exits in the
“RentalContract” it means this renter is former renter else, it is new renter. (f) As the model is presented here, what information must always be available for any
rental contract in the database? (3 things)
According to this model, registered renter personal details will always remain in the database.
And these renters are called former renters. “RentalContract” entity has the renterid and rented
appartementid. So by renterid we can access the renter personal details from the “Renter” entity
table and by appartmentId we can access renter’s apartment details.
(g) The office manager has suggested adding a “used-by” relationship between Furniture
and
the
Renter.
What
is
your
reply
to
this
suggestion?
Why?
First we have to remove the EFGH relation between “RentalContract” and “Furniture”.
then we can create used-by relation between “Renter” and “Furniture”. And (h) What happens if the person who is the owner of a building rents (leases for his or her
own use) an apartment in that building? Explain the effect on the database.
Current database design will support this change. There will not be any effect on the database.
The relation “J” shows that an apartment can has zero or more renters so it simply specifies that
there may be number of apartments in “Apartment” table that need not to be rented.
(i) If 4 college students share a 2-bedroom apartment, how many rental contract instances
will the roommates have to sign?
There will be four instances of rental contract. Each renter student has to registerd with the
system so the Renter will have four instances for these four students. And each renter has to sign
the contract for an apartment so four renterids with same contracte id and with same apartment id
will be created in “RentalContract”. The A relation shows that A “RentalContract” can be signed
by many renters. Same the relation I shows that an apartment can be rented by many rental
contracts.
(j) One feature of this model will never be used because it exceeds a physical limitation of
the real world. Identify the item and describe the physical limit.
The concept of furniture will be unused and wasted according to this database. Let’s assume we
have fixed some furniture to a particular apartment or building and then a customer wants to rent
an apartment and does not want to rent furniture for this reason. At that point it became tough to
handle the database because according to this situation we have to shift this furniture to not
rented apartment. And now this become a very difficult to maintain furniture for each apartment.