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Ch.2 Data Organization and Data Control - Coggle Diagram
Ch.2 Data Organization and Data Control
2.1 data input and sources of error
transcription error
data is read or typed incorrectly
e.g. 1& I& l, 0 & O
transposition error
2 consecutive digits are swapped
e.g. 61 & 16
data source error
provide incorrect data
e.g. report an incorrect tel no.
GIGO
Garbage-in-garbage-out
2.2 data control
data validation
-> rules making sure data is reasonable
fixed value check:
be one of the values in a pre-defined list
range check:
whether within a range of no
format check:
data follow the known patterns
field length check:
whether have the correct no of characters
check digit:
e.g parity check
field presence check:
ensure all necessary fields are present
Type check
data verification
-> check whether the inputted data matches
input data twice
double data entry
2.3 data hierarchy
field
e.g. tel no, email
record:
collection of fields
table:
collection of records
database:
collection of tables
2.4 database management system (DBMS)
SQL command
features
filter
sort
index
data entry forms:
provide a user- friendly environment
data validation, e.g. range check & type check
query
reports
2.5 file access modes
sequential access mode (outdate):
e.g magnetic tape -> seek time is long
direct access mode (random access):
e.g hard disk