Consider the ER diagram shown in Figure 7.21 for part of a BANK database. Each bank can have multiple branches, and each branch can have multiple accounts and loans.
(a) List the strong (nonweak) entity types in the ER diagram.
(b) Is there a weak entity type? If so, give its name, its partial key, and its identifying relationship.
(c) What constraints do the partial key and the identifying relationship of the weak entity type specify in this diagram?
(d) List the names of all relationship types, and specify the (min,max) constraint on each participation of an entity type in a relationship type. Justify your choices.
(e) List concisely the user requirements that led to this ER schema design.
(f) Suppose that every customer must have at least one account but is restricted
to at most two loans at a time, and that a bank branch cannot have more than
1000 loans. How does this show up on the (min,max) constraints?
(a) Entity types: BANK, ACCOUNT, CUSTOMER, LOAN
(b) Weak entity type: BANK-BRANCH. Partial key: BranchNo.
Identifying relationship: BRANCHES.
(c) The partial key BranchNo in BANK-BRANCH specifies that the same BranchNo value ay occur under different BANKs. The identifying relationship BRANCHES specifies that
BranchNo values are uniquely assigned for those BANK-BRANCH entities that are related to the same BANK entity. Hence, the combination of BANK Code and BranchNo together constitute a full identifier for a BANK-BRANCH.
(d) Relationship Types: BRANCHES, ACCTS, LOANS, A-C, L-C. The (min, max) constraints are shown below.
(e) The requirements may be stated as follows: Each BANK has a unique Code, as well as a
Name and Address. Each BANK is related to one or more BANK-BRANCHes, and the
BranhNo is unique among each set of BANK-BRANCHes that are related to the same BANK.
Each BANK-BRANCH has an Address. Each BANK-BRANCH has zero or more LOANS and zero or more ACCTS. Each ACCOUNT has an AcctNo (unique), Balance, and Type and is related to exactly one BANK-BRANCH and to at least one CUSTOMER. Each LOAN has a LoanNo (unique), Amount, and Type and is related to exactly one BANK-BRANCH and to at least one CUSTOMER. Each CUSTOMER has an SSN (unique), Name, Phone, and Address, and is related to zero or more ACCOUNTs and to zero or more LOANs.
(f) The (min, max) constraints would be changed as follows:
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