Question 1

What is a database?

Accepted Answer

A structured persistent store of data. Stored on the secondary storage devices of a computer system Provide security, auto backups and users with controlled access to data they need

Question 2

Benefits of databases?

Accepted Answer

- Make it fast to: access data, update data, search for data and present data in a suitable way

Question 3

What are the layers of a Database?

Accepted Answer

External level: What the user sees. Acts like a filter on data in the database Designed to be useful for a particular job. User friendly UI. Hides unnecessary/restricted data. Allows user to interact with DB Conceptual view: Describes structure of DB, entities, attributes, data types, relationships, validation, tables. Hides details of physical storage structures Physical: How the data is actually stored in the DB, works with OS and DBMS to store and retrieve data from storage devices

Question 4

What is data security?

Accepted Answer

Keeping data safe from accidental or deliberate loss and malicious attacks. Controls Who has access to the database and what they are permitted to do

Question 5

What are files?

Accepted Answer

Data stores on a computers secondary storage medium that have names and are stores of binary data Can be a program, word processed document, image or music

Question 6

What are serial data files?

Accepted Answer

Records organised one after another Only possible way to storage files on mediums such as tape Each data file is as large as the data to be stored No empty records = efficient Slow as it has to read through each data record until relevant record is found If data is modified then the complete altered file has to be re-written back to storage medium. Temp file created and replaces original until process is complete

Question 7

What are sequential data files?

Accepted Answer

Same as serial but records are stored in order of a designated key field (Eg: alphabetical) Records can be found easier Data modification still raises same issues as serial Not great for data that has no particular order as data has to be sorted often

Question 8

What is indexing?

Accepted Answer

Speed up searches Software searches for the start of the right section (like a book chapter), then directs the search to the right part of the main data store. After that a sequential search can look for the item required Records match length of data to be stored No wasted space Deleting a record will only delete index number, data still remains New records are added to end of files and index number is increased Eventually DB will have large amounts of wasteful data that is not indexed. Can be solved by rewriting the file and therefore removing any un-indexed data and re-indexing the rest

Question 9

What is an indexed sequential data file?

Accepted Answer

Used for large Sequential Data Files - Stored in order of key field AND index

Question 10

What is a random access data file?

Accepted Answer

Each record is ID with a record number in sequence and each record occupies same space Quick access to data as it can calculate position based on record number Wasteful of storage as EVERYTHING is stored with same amount of memory Each time new file is added it is added to the end and the RN is Incremented When records are removed only the data is deleted, leaving an empty record. Overtime there can be many blank records

Question 11

What are fixed length fields?

Accepted Answer

Suitable amount of space In a file is reserved for data Any unused bytes are packed with a character such as a space Less space efficient however processing is more straightforward because bytes can be counted to reach desired point. (After set ‘n’ number of bytes you will move onto next field) Quick to search

Question 12

What are variable length fields?

Accepted Answer

Only store as much data as is needed. Eg “Fred’ takes 4 bytes and ‘Jennifer’ takes 8 bytes Space efficient Processing is harder as finding a particular record requires checking all the preceding entries sequentially

Question 13

What is a flat file database?

Accepted Answer

Simple databases with one table A single spreadsheet is an example used for simple data-handling requirements

Question 14

What is a relational database?

Accepted Answer

Multiple related tables Each table represents a single entity (real world object or person) Required for the storage of more complex data Tables are linked via common attributes to create relationships (Primary keys —> foreign keys) Reduces amount of duplicated data Entity is anything about which we store data. They have attributes (characteristics eg: student name, ID, subject level) Tables consist of Tuples (records)

Question 15

What is a hierarchal database?

Accepted Answer

Multiple tables Tree like structure Each child node linked to parent node

Question 16

Structure of relational databases? (Including primary, secondary and foreign keys)

Accepted Answer

Use fixed length fields Each column contains 1 data type No rule about order of rows in a table. When order is required indexes are added No rule about order of columns No two rows can be identical One column must be primary key therefore making each row unique Primary key is used to link a table to the foreign keys of other tables. Relationships link them together and are produced by having repeated fields across tables (foreign key) Secondary keys are not necessarily unique but can be useful for quick searching

Question 17

What are entity-relationship diagrams? Draw a one-to-many relationship, many-many relationship and one-one relationship

Accepted Answer

- A data modelling technique used to define a relational database RELATIONSHIP DIAGRAMS CAN BE FOUND IN PHOTOS -In relational databases we want tables to be related by one-to-many relationships -A one-to-one relationship suggests that 2 entities should be in the same table -A many-to-many relationship suggests the need for at least one more table to separate entities

Question 18

What is hashing?

Accepted Answer

Method of transforming a string of characters in a record into a shortened form that can be used as a disk address This shortened form can be used to access a record from a database more easily than by using the complete original string Typically multiple records can produce the same hash values. In this case the data is located in the next available space on the storage medium, so some serial searching may be necessary

Question 19

What is data redundancy?

Accepted Answer

Unnecessary duplication of data in database - Repeated fields etc. We need some repeated fields to make links but to many leads to errors and wastes storage space

Question 20

What is referential integrity?

Accepted Answer

ensures data integrity. Referential Integrity refers to the accuracy and consistency of data within a database. REMEMBER ###Makes sure all foreign keys link to an existing/valid primary key. Also makes sure if a primary key is deleted/updated, foreign keys are no longer valid

Question 21

What is a DBMS? What does it create and what does it provide?

Accepted Answer

Database management system that creates and maintains a database. Eg: Microsoft Access Creates and uses: the structure, queries, views, individual tables, interfaces and outputs Provides: security, backups, index updating, enforcement of referential integrity and facilities to update and interrogate the DB

Question 22

What is transaction processing?

Accepted Answer

attempts to provide a response to the user within a short time frame. not as time critical as real time features limited range of operations planned in advance, such as a bank account balance enquiry or withdrawal

Question 23

What is CRUD?

Accepted Answer

relational databases must have certain basic functionality to be useful Create, Read, Update, Delete match to; INSERT, SELECT, UPDATE, DELETE. SQL commands 3 of the commands result in transaction taking place

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