Chapter Five: Databases Flashcards
Explain what is meant by the term ‘validation’.
Validation is the process of checking data when it is input. Validation is carried out by software, and not humans, not by humans. It checks that data confirms to certain rules.
What is meant by a range check?
A number must fall between certain limits.
Explain what is meant by the term ‘verification’.
Verification is checking that the data being entered is correct. It can be a simple visual check against the source data or an algorithm checks two copies, entered independently, and flags up inconsistencies.
What is a digit check?
Must be exactly the same as data previously entered. An algorithm calculates an extra digit which is appended to the data. The same algorithm checks data when input.
Explain what a DBMS is. (3 marks)
DBMS stands for Database Management System. This is software that looks after a database at a fundamental level.
What is a database? (3 marks)
A database is a structured set of data held in a computer, especially one that is accessible in various ways.
What is a flat-file database?
This is just rows and columns such as would be suitable for an address book.
Explain what a relational database is.
Relational databases are the most useful model and consequently the most common type of database. They are far more flexible than other models and can replace other models in most cases.
Explain the difference between an entity and a table.
In a database, anything about which information can be stored; for example, a person, concept, physical object or event. Whereas a table is where the data is stored. The DBMS provides tools for creating and modifying tables.
Describe two ways in which a query can be constructed.
Query by example (QBE) uses a graphical interface that lets the user assemble the fields and conditions required for a query.
Alternatively, a query can be built from a query language such as SQL (Structured Query Language). SQL and other query language make it possible to write programs that extract the data required.
Name four different data types and give an example for each.
Number data: Number of items ordered, given in the form of an integer.
Text data: An invoice amount.
Date/time data: Date started employment.
Yes/no (Boolean): Entered for an exam (or not entered).
Describe the difference between the AND operator and the OR operator.
The AND operator: Checks that two conditions are true then selects the data that matches these conditions.
The OR operator: Checks that either of two conditions are then selects the data that matches these conditions.
What is a transaction?
When a change takes place in the database. Transactions must not damage the integrity of the database.
Name six validations methods and give their meanings.
Length check: Must be below a certain number of characters or be above or below a certain limit.
Type check: No numerals allowed in a surname.
Range check: Date of birth fir a job applicant.
Presence check: Surname when applying for a job.
Lookup check: Check that a password is correct.
Format check: Car registration number must be LL/NN/LLL.
Explain what will happen if there is an error in a database.
Firstly, it can result in embarrassment such as sending bills to customers who have died. Secondly, it could result in a financial loss, such as if a bank account is wrongly credited or debited. Finally, it can result in life or death situations, such as incorrect navigational data for aircraft.
