4d Explain Distributed Databases ***

Question 0

The Mountain Rescue team is part of a regional Mountain Rescue Organisation which holds details of all its members in a regional database. This database needs to be distributed to each Mountain Rescue Team.

Explain an advantage to the regional Mountain Rescue Organisation of using a central database with remote local indexes.

Answer 0

 storage is only required at the central location for the centralised database (1) the local indexes stored at each site take up far less memory (1)
 queries are processed locally(1) this speeds up searches as only the required data is retrieved from the central location (1)
 less data traffic than complete centralisation (1) as only data is sent and not the additional information /forms/reports structure (1)  increased security (1) only central database needs increased
security as that is where the data is stored (1
 integrity of data not compromised (1) as it is stored in only one
location and one database to update (1)
 centralised back-up of data (1) management backup easier as one person’s responsibility (1)

Question 1

The database is distributed across the hotel chain.

Describe three different approaches to the distribution of databases.

Answer 1

One mark for method, one for expansion:
 partitioned between sites / hotels (1) each separate hotel in the chain holds data on that particular sit(1)
 partitioned horizontally(1) database split between
sites/departments by fields (1)
 partitioned vertically (1) database split between sites/departments by fields (1)
 database duplicated between sites (1) a full copy
indexes are held at each hotel (1)
 one central database (1) relevant/site specific indexes are held at each hotel (1)

Question 2

The Mountain Rescue team is part of a regional Mountain Rescue Organisation which holds details of all its members in a regional database. This database needs to be distributed to each Mountain Rescue Team.
Explain how the regional Mountain Rescue Organisation could make use of vertical partitioning.

Answer 2

One mark for point (max 2), one for expansion (max 3)
 only certain people see certain fields (1) financial matters not
revealed to all (1)
 to conform to the law/DPA (1) keeping personal information private (1)
 reduces amount of data being sent between locations (1) in order to speed up data transfer (1) allowing faster reaction time (1)
meaning rescue reaches emergency quicker (1)

Question 3

The dental surgery’s custom-written patient database system is to be modified for use by both
parts of the surgery.

Define what is meant by vertical partitioning of a database.

Answer 3

Data is separated based on fields.