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chapter 2:Data Organization and Data Control (2.4 DBMS (DBMS: manage the…
chapter 2:Data Organization and Data Control
2.1 DATA INPUT AND SOURCES OF ERRORS
3 different sources of error
transcription error
transposition error
data source error
GIGO:production of inaccurate information
2.2 Data Control
Data validation
Comparing data with a set of rules or value
Make sure data is reasonable&valid
Check digit
to check if a number is valid
ISBN
HKID
Data verification
to check if the inputted data matches that in the document
Input data twice
Double data entry
Database system
orginized to hierachy
Record
collection of related fields
contail information of one specific identity
data can be used to identiy records from the others
Table
collection of related records
contain entities stored in specific record format
records have different values in key filrd
Field
the smallest unit
represent a fact of record
can be numberic,text,date,Boolean,etc
Database
collection of releated tables
link records from different tables dynamically
2.4 DBMS
database: collection of interrelated data
in a table
DBMS: manage the database structure
store organize retrieve data
DATABASE SEVER:MY SQL,MICROSOFT SQL SEVER
small office and personal use:MICROSOFT ACCESS,FILEMARKER PRO
organizing tables:creating modifying deleted tables
managing table records:
adding deleting modifying browsing records
see book p.68
2.5 File Access Modes
Sequential Access Mode
Long seek time
Unpredictable when records are retrieved randomly
e.g. Magnetic tape
Direct Access Mode
Predictable
e.g.Hard disk
Short seek time
2.3 Data Hierarchy
S4A Brigitte(2)
Sinnia(9)
S4B Nicole(6)