Section 4 Exchanging Data Flashcards
Why compress sound and images?
Reduces size of files enabling images on websites to load quickly, and reducing buffering when streaming videos online
Lossy compression
removes non essential info
reduces FS at cost of quality
Lossless compression
records patterns in data rather than actual data
computers can reverse the process and reassemble an image
larger file than lossy but nothing is lost (obviously)
define entity
a category of object, person, event or thing of interest to an organisation about which data is to be recorded
eg employee, product, ingredient
they have attributes
flatfile database
consists of a single file
Define composite primary key
one consisting of more than one attribute
define relational database?
collection of tables in which relationships are modelled by shared attributes
what is an attribute on a table
a field (column)
How to link database tables?
use of a primary key from another table combines with a table’s own one, one being a foreign key
4 ways to capture data
multichoice forms read using OMR or others with OCR
smart card readers
scanners eg in airports to scan passports
barcode readers
How to select data
Query by example
only added to database when matches specified criteria eg speed cameras only capturing vehicle regs above the speed limit
SQL
selects from tables which match criteria
How to exchange database data
via electronic data exchange (EDI)
used by exam boards to send schools exam results
