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Chapter 3 Database systems (1) - Coggle Diagram
Chapter 3 Database systems (1)
Database
Usually a group of files
Critical component of information systems
Collection of related data that can be stored in a central location or in multiple locations
DBMS - Database management systems
Software for creating, storing, maintaining, and accessing database files
Make the use of a database more efficient
Logical database design
Physical view
How data is stored on and retrieved (CD's or hard drives)
Logical view
How information appears to users
How it can be organized and retrieved
Can be more than one logical way
Two ways information is viewed in a database:
File access methods
Random access
Fast accessing few records
Records can be accessed in any order
Independent sequential access
Combination
Like a book index
Sequential access
Usually used for backups and archieves
Records are organized in a sequential order
What is a data hierarchy
Record - group of related files
File - Group of related records
Structure and organization of data, which involved fields, records and files
Database design : Data models
Determines how data is created, represented, organized and maintained
Data model's 3 components
Data structure
Describes how data is organized and the relationship among records
Operations
Describes methods and calculations that can be performed on data
Integrity rules
Defines boundaries of a database i.e. min / max valuue
Benefits of a database
Storage space is reduced
Improved data management
Data and programs are independent
Variety of relationships among data can be maintianed
Data redundancy is eliminated or minimalized
Relational database model tools
Foreign key
Is a field in a relational table that matches the primary key column of another table
Used to cross reference tables
Normalisation
Improves database efficiency by eliminating redundant data
Primary key
Uniquely identifies every record in a relational database
Types of models
Network model
Similar to the hierarchical model, but records are organised differently
Relational model
Rows are records
Columns are fields
Uses a 2-D table of rows and columns of data
To begin designing a relational database, you must define the logical structure by defining each table and the fields in it
Data dictionary - stoves collection of definitions:
-Field name - Student name, admission date, age, major
-Field data type - character (text), date, number
-Default value - i.e. no major - undecided
-Validation rule - ie. student age cant be negative
Hierarchical model
The relationship among records form a tree like structure