Flashcards in Data & Information Deck (54):
Raw facts and figures which are meaningless as they have not been processed e.g. 3
Data that has been processed and has meaning e.g. My sister is 3 year old
Why code data?
(i) faster to type than full words, taking less time to enter data
(ii) faster for the computer to perform sorts and searches on data
(iii) codes are often designed to be unique
What is a database?
A collection of information
Advantages of databases on a computer
- large amounts of data is stored in a small space
- a computer can search the database quickly for specific information
- the stored data is less likely to be lost
- more than one user can see the data at any one time
Disadvantages of databases on a computer
- the computer equipment you need will be relatively expensive to buy and install
- initial cost of collecting the data and setting up the database will be high
- to make the system effective, staff need to be trained
- if the system fails you cannot access the information
Text - letters, symbols, numbers (alphanumeric)
Number - number only (can include decimals)
Date/time - dates and times
Currency - for all monetary data (includes currency symbols)
Yes/no - or true/false
Autonumber - a unique value generated by Access for each different record
What is a key field/primary key?
A field that uniquely identifies one record in a table
What is a datafile?
Collection of related records stored in a table with field headings
What is a record?
All the data connected with one item organised under field headings
What is a field?
The column which holds the data
What is an item?
One field in one record
What is a flat file?
A database containing only one table with all records contained in this table under the field headings. Can be described as a file containing text or data separated by commas or tabs such as in a csv file
What is a relational database?
A database made up of a group of tables which are linked
What is data redundancy?
Data unnecessarily duplicated
What is data integrity?
Data that is accurate and up-to-date
What is a link field?
A field in two tables
Examples of forms
National lottery ticket selection form
Registering pupils in school
Multiple choice test
How does the optical mark reader (OMR) work?
It detects the presence of your pencil mark by reflecting light onto it - less light is reflected where a mark has been made.
The OMR then interprets the pattern of marks and sends the results to the computer for storage, analysis and reporting
Advantages of optical mark reader (OMR)
- a fast method of inputting large amounts of data - up to 10 000 forms can be read per hour depending on the quality of the machine used
- only one computer needed to collect and process the data
- OMR is much more accurate than data being keyed in by a person
Disadvantages of optical mark reader (OMR)
- if the marks don't fill the space completely, or aren't in a dark enough pencil, they may not be read correctly
- not suitable for recording one out of a selection of answers, not suitable for text input
- the OMR needs the answers to be on the prepared forms which will all be identical to one another (you can't just pick up a blank sheet of paper and mark your answers on it)
An optical character recognition (OCR) system consists of…
A normal scanner and some special software
How does an OCR system work?
The scanner scans text on a document or piece of paper into the computer
The special software then examines the page and changes the letters into a form that can be edited or processed by a normal word processing package
What is OCR used for?
For postcodes on letters at sorting offices
In libraries to digitise old books
Advantages of OCR
- cheaper than paying someone to manually enter large amounts of text
- much faster than someone manually entering large amounts of text
- the latest software can recreate tables and the original layout
Disadvantages of OCR
- not 100% accurate, there are likely to be some mistakes made during the process (accuracy depends on how clear the writing is)
- all documents need to be checked over carefully and then manually corrected
- if the original document is of poor quality or the handwriting is difficult to read, more mistakes will occur
- not worth doing for small amounts of text
What is a barcode? What does it contain?
A series of vertical bars of varying widths that represents numbers which contain:
- a country code
- a manufacturer code
- a product code
Does not contain price as that's held in the company database
What is a barcode reader?
An automatic input device which is used to scan or 'read' the barcode by using a visible red light - the reflected light is translated into digital data that is interpreted by the computer to identify the product and price from the database
Main advantage of the barcode reader
Any price change only needs to be made to the database and not every single product package
Examples of things that have barcodes
- books (ISBN number)
- library tickets
- boarding passes
- concert tickets
What is a transcription error?
Any data entry error created when transferring data from one source to another source
Types of error
Omission errors explanation and examples
Data is left out
32 instead of 321
Transposition errors explanation and examples
Characters being typed are swapped by mistake
312 instead of 321
Duplication errors explanation and examples
Entering a character twice
3221 instead of 321
What is data verification?
A method of checking data carried out by a person to check data is correct before it is processed
What is data validation?
A method of checking data carried out by a computer to check data is correct before it is processed
Types of data verification
(1) double entry - the data is keyed in twice and both versions must be identical
(2) proof reading - after data is keyed in, it is read to check it has been typed accurately
Types of data validation
(1) range check
(2) presence check
(3) format check
(4) length check
(5) type check
(6) lookup tables
(7) check digit
What is a range check?
A check carried out on a number or date field to make sure the data falls within a specified range
E.g. Exam %s can have a range check of between 0 and 100
What is a presence check?
Ensures that important fields are not left blank
(In MSAccess set required field to 'yes')
What is a format check?
Data must match a preset pattern
E.g. A post code must have a certain combination of letters and digits
(In MSAccess use an input mask)
What is a length check?
Ensures data is of a specified length
E.g. A credit card number must have 16 digits
(In MSAccess set the length field for text items)
What is a type check?
A check carried out on a number or date field to make sure the data entered is of the correct type
What are lookup tables?
Ensure that the data entered is one of an acceptable set of values
Such as Y or N, M or F
What is a check digit?
An extra digit added to a numeric code to ensure that it is valid. The extra digit is calculated by applying a formula to the sequence of numbers
Used on barcodes on supermarket items and on the ISBN number on the back of books
Advantages of databases
- information is usually only stored once
- files can be linked together so that updates are automatically made to each file that shares information
- the record structure can be easily altered even though lots of data has already been entered
- access to information is fast using queries
- validation checks can be made as data is entered ensuring fewer mistakes are made
Disadvantages of databases
- if the computer breaks down you are not able to access information
- computer files are easily copied - this can be a problem therefore all sensitive information must have protection - usually by password
- training is needed to use the system which can be expensive and takes valuable time
Why is data compression used?
To save space or reduce download time
Advantage of data compression
Easier to send
Disadvantage of data compression
It must be decompressed before it can be used
Graphics can be compressed using
JPEG or GIF format
Music files can be compressed using