Please enable JavaScript.
Coggle requires JavaScript to display documents.
Data Organization and Data control - Coggle Diagram
Data Organization and Data control
Data Hierarchy
Record
It is a collection of related fields.
Contain information of one specific entity
The data in a key field can be used to uniquely identify one particular record from the others.
Table
It is a collection of related records with identical record structures. Contain the information of all entities stored in specific record format.
All records in a table have unique and different values in key field.
Field
It is the smallest unit of data that can be accessed by a user. Represent a specific fact of a record.
Can be of type: numeric, text, date, Boolean, etc.
Database
It is a collection of related tables.
May link records from different tables dynamically with one or more key fields.
Database Management system
Database server
MySQI, Oracle Enterprise Manager, Microsoft SQL Server
Small office and personal use
Microsoft access , Microsoft Visua; FoxPro, FileMaker Pro
Basic Functipns to Organize Tables
Create table
Create a new table and specify the record structure.
Modify table
Change the structure of an existing table.
Delete table
Remove a table from a database. All records in the table will also be deleted permanently.
Basic Functions to Manage Records in a Table
Add a new record
Create a new record. Users are subsequently able to input information into it.
Delete existing records
Remove unwanted records from a table.
Users can issue a delete command with a condition
statement such that all records matching the condition will be deleted at one time.
Browse records
Display all or part of records of a table in a window.
Users may also be allowed to add, modify or delete
records in the browse window.
Modify exiting records
Change the field values of selected records.
Users can issue an update command with a condition
statement such that all records matching the condition will be changed at one time.
Essential Features for Database Management
Filter
Allows users to specify a filtering condition
Only the records that satisfy the condition are
accessible in the database table.
The unmatched records are hidden temporarily
until the filter constraint is released.
Sort
Change the order of records according to the value of one or more fields in a table.
The sorted records are usually saved in a new table.
Allows records to be rearranged in a specific order permanently
A slow process if the number of records is large
Index
One index file refers to one instance of a
specific table only.
An index file must be re-indexed when values of the field involved in the index expression have been changed
The index keys are created and
arranged according to the index expression.
The index files are usually small relative to the
referred table.
A small file containing a number of index keys.
They can be loaded into the main memory for
speeding up the access process.
Data Entry Forms
Can be treated as the interfaces for adding or modifying records
advantages
Perform data validation such as
range check and type check of test marks
Perform data validcation such as
double data entry of renewal password
Simplify data entry with features like pull
down menu, check box and list box
Modify related records from two or more tables
in one form
Provide a user-friendly environment for data
entry
Query Formd
Provide an interface for users to extract and display records which match the specified conditions
The extracted data can further be modified, deleted or stored in a new table.
Advantages
Can be stored and are reusable
Able to show data from two or more tables
Able to display calculated results using the extracted records
Writing commands in Structured Query Language (SQL) is another way to enquire about results from a database.
Reports
Used to display results on the computer screen or produce hard copies with a printer in the defined format
Advantages
Can be stored and are reusable
Able to display data and calculated results from
two or more tables.
Able to print results in specified locations, styles
and formats accurately
Data Control
Data validation
Fixed value check
Ensure that the data conforms to be one of the values in a pre-defined list
Range check
Ensure that the data alue is within a pre-determined range
format check
Ensure that the form of data follows some known patterns
Type check
Ensure that the data type are correct
Field length checck
Ensure that the data has the correct number of characters or digits
Check dighit
It is used for self-checking. With numeric data, check digit is calculated using a mathematical formula and this is then attached to the end of the number. When the check digit of the number matches the digit calculated from the number, the number is confirmed valid. Parity check is a common application of check digit in digital data transmission.
field presence
Ensure that all necessary fields are present
Data Verification
Input Data twice
Double Data Entry
Data input and source of error
input devices
scanners,
sound
recorders
senors
digital video cameras
keyboard
error
data source error
Data source providers
provide incorrect data.
transcription error
Data is read or typed in
incorrectly.
transposition error
Two consecutive digits are
swapped.
File Access Modes
The access mode used to access database records depends on which media the database
resides in.
Squential Access Mode
The seek time is long and unpredictable when records are retrieved randomly.
Not a common medium for storing frequently used data records
Need to be wind the tape forward or backward until the desired record is just underneath the read/write head before the reading or writing operation can proceed
Mainly used for backing up and recovering of database and data files in computer servers
Data records are stored one by one along the lengthy magnetic strip.
Direct Access Mode
Once the target location is moved under the read/write head, the read/write operations can proceed.
The seek time is much shorter and predictable, ranging from 8 ms to 20 ms.
During the data is read from or written to a hard disk, the magnetic disk plate (platter) rotates and the read/write head moves across the platter surface at the same time to the location containing the data.
The most essential secondary storage device for a computer system
The most common storage medium for secondary storage due to its high reliability , speed and capacity.
Other examples are floppy disks, DVD-RAM and CD-RW
They are limited in capacity and speed of data access.
They are rarely used as the storage media for database systems and frequently used data files.