Databases
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Give two types of VERIFICATION
• Visual check- checked by a human to see if it is correct 2. Double entry- when the data is entered twice and neither are accepted if they are different
Explain why it is desirable to separate the data in a database from the applications used to manage the database
If the data is separate from the application using it than the database can be used by more than the one application ie. The data can be shares. This avoids the need to duplicate data for each application
What does DBMS stand for?
DataBase Management System
What is the difference between a simple and a complex query?
Simple- looks for data in only one field Complex- looks for data in multiple fields
How does DBMS create data?
It allows data to be inserted into the relevant table. It can also check that the data is valid and complies with any rules set up.
Give some advantages of computerised databases over paper-based databases
• Data can be accessed by more than one person • Can easily sort the data in different ways • Easy to update the data • Can restrict access to the data so that different users can see different data • Easy to search for specific information • Updates are immediate and shared with all users • Easy to present data in different forms eg. Graphs
What is a persistent store of data?
The data is stored even when the application or device is no longer running
What does related mean, in terms of databases?
The data in one table is linked with the data in another table eg, an order (one table) is linked with a customer (another table)
Explain the following terms A) field B) primary key C) record D) table E) File
A) a single set of data (a column) B) a unique value used to identify each record in a table and link it to a different table C) a set of data about a person/ thing (a row) D) stores all the records for a thing E) the actual file that holds the database/ a table
How does DBMS interrogate a table?
It allows data to be queried (using SQL)
Explain how a DDL and a DML are used to manage database files
DDL- Data Definition Language, used to create tables and rules DML- Data Manipulation Language, used to insert/update/delete/query the data
Explain the difference between VALIDATION and VERIFICATION
VALIDATION - chicks that the data is: ~ sensible/ reasonable ~ within acceptable boundaries ~ complete VERIFICATION is confirmation that the data itself is correct, eg double entry/ visual check
Give 4 types of VALIDTION checks
• Range - that the number isn’t too big/ too small • Length- that the text entered isn’t too long/ short • Presence- that data has been entered in the correct fields • Format- that the data is in the right data type eg, there are no letters in the age box
Give 2 examples of VERIFICATION that might be used in computer systems
• When entering and email address 2. When changing/ creating a password
How can DBMS be used to create applications?
The DBMS allows things like: Tables- to hold the data Relationships- to link the tables Access rights- to control people’s access to the data Queries- to allow the database to be searched Forms- to allow user friendly input of data Reports- to present the data in a useful and meaningful way
Explain the difference between DBMS and a database
The DBMS manages the data whilst the database is the data.
How does DBMS maintain data?
It allows data to be changed/ deleted. It can also check that the data entered complies with any rules set up (VALIDATION)
What three things should data handling software be able to do?
• Create data • Maintain data • Interrogate data
Use SQL to add the following data into the product database: | Product code | name | cost | supplier code | quantity | | 101AA | sandy| 21 | 63 | 40 |
INSERT INTO product VALUES ( ‘101AA’, ‘sandy’, 21, 63, 40)
Select the name and cost of a shoe that costs less than £50 and has a supplier code of 63 from the database product.
SELECT product.Name, product.Cost FROM product WHERE product.cost
Change the supplier code to 62 for the product of code 367HT in the products table.
UPDATE product SET product.suppliercode = 62 WHERE product.productcode = 367HT