Chapter 16 - Relational Databases

Chapter 16 - Relational Databases

1. Describe the role of Database Admin (4)

   • Defining, modifying or the db's structure, tables, keys and data. Controlling access to the db through access rights. Desinging queries, forms and reports. Keeping users informed of relevent changes. Installing and upgrading the DBMS. Establishing backup and security

2. Explain what is

   • flat file
     • A database system in which each database contains a single file which is not linked to any other file
   • data inconsistency
     • A particular attribute which is stored more than once in a database and has different values
   • Explain data independence
     • Data is kept seperate from the software/ programms which use it
   • data integrity
     • The accuracy or reliablilty or completeness of data
   • Primary Key
     • It uniquely identifies a record
   • Composite Key
     • Consists of two or more key fields, each of which may a primary key in another table
   • Foreign Key
     • Referential constrant or link between 2 tables. Or attribute in one table primary key in another
   • Data Integrity
     • Integrity refers to the validity/ accuracy of the data which can be affect by user error
   • Data consistency
     • Data consistency is a particular attribute which only has 1 value at particular time

3. Explain the problems caused by data redundancy

   • Non-key data gets stored more than once in the database. This increases the memory needed to hold the database and increases data reterival times and aaffects data integrity and consistency
   • Explain the drawbacks of using a flat file in this case

4. What can end users do

   • Run queries, reports and macros

5. Two drawbacks of non-normalised data

   • Data may be inconsistant. A attribute may have more than one value. Some data may be redundant, a value is held on more than one table

6. 2 benefits of normalised data

   • Data redundancy is eliminated as each non-key attribute is only stored once. Data consistency is ensured, data intrgrity and data independence

7. Describe each stage in normalising data

   • 1NF - Remove repeating groups 2NF - Remove fields not dependent on primary key/Remove non-key depedencies 3NF - Remove fields that depend on other non-key fields