Distributed databases

Question 1

Distributed database vs distributed processing

Answer 1

Dp, Shares the database’s logical processing among two or more physically independent sites while DD, Stores a logically related database. The sites are
connected by a computer network.

Question 2

Database Fragments

Answer 2

database is composed of several parts know as database fragments.

Question 3

In DD, do the user need to know the location and the name of each database fragments ? YES or NO

Answer 3

No, they dont have to, because it’s transparent to the user

Question 4

Do distributed processing requires distributed database ? Does the data need to be reside where the processing is stored ? YES or NO

Answer 4

No, that’s optional. The data can reside in the same space but it’s not necessary.

Question 5

Does a distributed database requires distributed processing ? YES or NO

Answer 5

Yes, but not the other way around.

Question 6

Distributed Database Management System (DDMS) advantages

Answer 6

• data can be stored at ‘greatest demand’ site that improved Performance
• Improved Reliability – data replication
• Growth facilitation
• Reduced operating costs

Question 7

DDMS Disadvantage

Answer 7

• Cost
• Complexity
• Database design more complex

Question 8

What is DDMS ?

Answer 8

Governs the storage and processing of a single logically related database OVER INTERCONNECTED COMPUTER SYSTEMS in which both data and processing functions are distributed among several sites.

Question 9

What’re the things to consider when you design the distributed database ?

Answer 9

• How to partition the database into fragments
• Which fragments to replicate
• Where to locate those fragments and replicas
  (More frequently used fragments should be stored locally Fragments used by all users should be stored centrally)

Question 10

What is data fragmentation ?

Answer 10

• Allows a single object to be broken into two or more segments or fragments
• Data fragmentation information is stored in the distributed data catalog (DDC), from which it is accessed by the TP to process user requests

Question 11

Different types of fragmentation

Answer 11

1. Horizontal
2. Vertical
3. Mixed

Question 12

Explain horizontal fragmentation

Answer 12

• The division of a relation into tuples (rows)

* Each tuple has the same attributes (columns) but the rows are fragmented

Question 13

Explain vertical fragmentation

Answer 13

• The division of a relation into subsets by attributes (column)
• Each subset is stored at a different node, and each fragment has unique columns – with the exception of the key column, which is common to all fragments

Question 14

Vertical fragmentation’s disadvantage

Answer 14

Transaction issues here because same record may need to be inserted into two tables (part of record into 1 table and other part into another table). If only 1 insert is successful; end up with inconsistent data.

Question 15

Data replication

Answer 15

Storage of data copies at multiple sites served by a computer network
Fragment copies can be stored at several sites to serve specific information requirements
* Can enhance data availability and response time
* Can help to reduce communication and total query costs

Question 16

Types of data replications

Answer 16

1. Fully replicated db - Impossible because of overhead, to store multiple copies of entire database
2. Partially replicated - Stores multiple copies of some database fragments at multiple sites
3. Un-replicated - Stores each database fragment at a single site and no duplicates