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(COMP334)midterm00F_sol.pdf
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Fall 2000 COMP334 Midterm Solutions
Question 1: (20%)
a) What are the similarities and differences between parallel and distributed database management systems?
Answer:
Similarities:
.
Both make access to DDBS transparent to users

.
Both support inter-query and intra-query parallelism, reducing the query response time


Differences:
.
PDBMS is homogeneous, while DDBMS may be homogeneous or heterogeneous

.
PDBMS is usually under one operating system; DDBMS is not.


b) Why is giving database objects unique names more complicated in a distributed DBMS?
Answer:
.
Each assignment of name would require to check all DBMS for the existence of that name.

.
Synchronization problems: each site lacks the instantaneous information of other sites.


c) Briefly discuss the ajor differences between the classical distributed database systems and the multi-database systems.
Answer:
From two aspects,
.
Architectural models of their management systems

i. Autonomy: DDBS is tightly integrated; MDBS is total isolation.
ii. Heterogeneity: Usually DDBS is homogeneous, but MDBS is heterogeneous.

.
Design


i. Strategy: DDBS is top-down; MDBS is bottom-up.
ii. Structure: DDBS must have a GCS; MDBS may not have it.
d) There are two possible architectures for multi-database systems: with or without the global schema. List the major differences between these two alternatives.
Answer:
.
With GCS, global external schemas are defined from GCS or the global database structure; Without GCS, global external schemas are defined from LCSs of related sites.

.
With GCS, MDBMS explicitly handles the global part of databases; without GCS, MDBMS does not need to do so.


Question 2: (25%)
A supply-part database consists of fur relations as shown below:

SUPPLIER
SNO SNAME COUNTRY
S1 SN1 USA
S2 SN2 INDIA
S3 SN3 CANADA
S4 SN4 CHINA
S5 SN5 INDIA
S6 SN6 USA
S7 SN7 CANADA
S8 SN8 INDIA

SUPPLY
SNO PNO QTY
S1 P1 60
S2 P1 70
S2 P2 60
S3 P3 55
S3 P4 96
S4 P2 65
S5 P2 70
S6 P4 96
S7 P3 72
S8 P3 80

PARTS
PNO PNAME COLOR
P1 PC 30
P2 CAMERA 27
P3 VIDEO 50
P4 HI-FI 62

COUNTRY
COUNTRY REGION
CHINA ASIA
INDIA ASIA
USA AMERICA
CANADA AMERICA

Let p1: REGION = ASIA, p2:REGION = AMERICA be two simple predicates. Let us further assume that there are only two regions.
a) Perform PHF of COUNTRY with respect to these predicates. Show the detailed steps and the result fragments.
Answer:
Set of simple predicates = {p1, p2}
Set of minterm predicates = {p1 p2, .p1 p2, p1 .p2, .p1 .p2}
Set of implications = {p1 ..p2, p2 ..p1}

After elimination and simplfication,
Set of minterm predicates = {p1, p2}

Therefore, there are two result gragments:
COUNTRY1 = REGION=ASIA(COUNTRY)
COUNTRY2 = REGION=AMERC