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2009-02-18 Jacaranda questions 2.4, 2.6

posted Feb 18, 2009, 12:35 AM by Unknown user   [ updated Mar 31, 2009, 2:22 AM by Eddie Woo ]
Questions 2.4

1. Name the data components of a flat file information system.

  • Database - an umbrella term for all the data used by the DBMS when operating a single collection of data.
  • File - a collection of data records, usually on a simple theme e.g. "sales"
  • Record - data describing a single entity e.g. data describing contact details (data) for a customer (entity)
  • Field - data describing common features of entities e.g. names
  • Key field - a field that contains unique data for every record. No two records may have the same key field data.
  • Character - a single symbol, such as the letter "f".
2. What additional components are found in a relational database?
  • Relationships - tables or files created by joining data from different databases.
  • Attributes - fields copied from parent databases. Attributes are columns in the table view.
  • Calculated fields - fields created by calculations using data from other fields.
3. What is a required field?
A required field is one that has data for every single record.

4. Why should relational databases be normalised?
Relational databases should be normalised to change the links to attributes to links to the original data fields. This improves the speed at which the database can be manipulated.

5. In what situations would a required field be needed in a database?
Required fields would be needed for fields that must be fulled for all entities to make them unique and meaningful.

6. What data validation operations can your DBMS software perform?
"AutoNumber" generates a unique number for a field, prevent the user from even modifying the data. This is particularly useful for the key field, and other fields which must be unique for every record.

Questions 2.6

1. How can a database be protected from accidental or unnecessary changes?
A database can be protected from accidental or unnecessary changes by:
  • Locking records - locking a part of the database from modifications as soon as it is opened by a user, preventing other users from making changes to that part of the database.
  • Allocation users access levels - this prevents unauthorised access, by preventing users without authorisation from modifying parts of the database that are "off limits" to them.
  • Using transaction and master files - the changes are made to the transaction file and merged with the master field after being checked for any unwanted changes.
2. Which storage devices use sequential data access?
Magnetic tapes use sequential data access.

3. How does offsite storage protect data?
Offsite storage safeguards data against theft and destruction.

4. What steps would a DBMS have to perform to get the latest copy of a record from a master file/transaction file system?
  1. Transaction file is updated
  2. Transaction file is checked for unwanted changes
  3. Transaction file is merged with master file
  4. New master field is copied and replaces the old transaction file
5. Using the terms online/offline, shared/distributed, direct/sequential, describe the information systems available for student use in your school.
  • Student Terminal Server: online storage. Shared, directly accessed.
  • Library catalog: online storage. Shared, directly accessed.
  • Intranet: offline storage. Shared, directly accessed storage. Stored offsite.
6. How does the school office or library protect its data?
The school office protects its data by constantly making backups of its data and by not making its data available on a large network.

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