Data

You must consider the type of data to be stored, and how it is to be stored and used before data is entered into, for example, a spreadsheet or database.

• Text - Any character - 'XY?/125.. - Names of items
• Integer number - Whole numbers - 192 - Number of people in a shop
• Real numbers - Numbers with decimal places - 12.99 - Prices, height, weight
• Date - time - 23/08/2014 - A date, eg 23rd August 2014
• Boolean - True or false - Only two choices: 1 or 0, yes or no, M or F - storing a person's gender
• Image - a graphic file - a photograph - a photograph on a membership card

Text can be used to store any type of data.

Calculations cannot be carried out on data stored as text but it can be sorted and searched. 

Telephone 'numbers' are stored as text because they can have spaces, dashes and leading zeroes.

If calculations are required on data, such as currency and dates, they have to be stored as numbers.

Data is collected for many reaons. The choice of method of capturing the data will depend on why it is needed and how it is to be used. 

DJs requesting songs to play on their radio programme could use instand messaging, social networks or email to allow the audience to send song suggestions.

Recording the votes in an election could be done with paper voting sheets or online forms.

To save space in a spreadsheet or database file, it can be coded.

Examples of coding include:

• Y or N instead of Yes or No
• M or F instead of Male or Female
• Mr instead of Mister
• Dr instead of Doctor

Every item in a stock database is given a code that can be searches for or sorted to order.

Data such as 'red, large sofa with arms' is more complicated than a code such as S_ARL and takes longer to process.

Data stored in a spreadsheet or database must be accurate as it is used to retrieve useful information.

There are two methods for ensuring data is accurate: verification and validation.

Neither method makes sure that the data us correct; only that it is entered accurately and is the right sort of data.

Verification checks that data is entered exactly as it is shown on the original data capture sheet.

Verification can be done by:

• A visual check - to see if the data in the computer system is the same as that on the original questionnaire.
• Double entry - data is entered twice, by different operators, for large amounts of data, so the computer system can check one set against the other. If any differences are found, the computer system will report the differences to the operators. 

Double entry can also be used, for instance, when the same individual enters a new passwork into an online form.

Validation uses rules to make sure that data is reasonable and abides by the rules set up when, for example, the spreadsheet or database was created.

Validation checks the data as it is entered to ensure that the data is allowed into the system.

Validation checks include:

• Presence check - Ensures that data is actually entered by the user
• Data type check - ensures that the data is the correct type 
• Format or picture check - Ensures that the data is in the correct format
• Range check - ensures that the data is within set limits
• Character check - ensures that only allowed characters can be entered and others are rejected

Other validation checks can be made on data. For example, a check digit is a digit added to a bar code and is a number calculated from the bar code digits.

When the digits are read from the bar code the check digit is calculated again to make sure that they have been read accurately.