05-09-2012, 03:01 PM
Database Management System
1Database Management.PDF (Size: 299 KB / Downloads: 70)
DBMS contains information about a particular enterprise
Collection of interrelated data
Set of programs to access the data
An environment that is both convenientand efficientto use
Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Online retailers: order tracking, customized recommendations
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
Purpose of Database Systems
In the early days, database applications were built directly on top of file systems
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation —multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become “buried”in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
Instances and Schemas
Similar to types and variables in programming languages
Schema–the logical structure of the database
Example: The database consists of information about a set of customers and accounts and the relationship between them)
Analogous to type information of a variable in a program
Physical schema: database design at the physical level
Logical schema: database design at the logical level
Instance–the actual content of the database at a particular point in time
Analogous to the value of a variable
Physical Data Independence–the ability to modify the physical schema without changing the logical schema
Applications depend on the logical schema
In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.
Transaction Management
A transactionis a collection of operations that performs a single logical function in a database application
Transaction-management componentensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.
Concurrency-control managercontrols the interaction among the concurrent transactions, to ensure the consistency of the database.
1Database Management.PDF (Size: 299 KB / Downloads: 70)
DBMS contains information about a particular enterprise
Collection of interrelated data
Set of programs to access the data
An environment that is both convenientand efficientto use
Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Online retailers: order tracking, customized recommendations
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
Purpose of Database Systems
In the early days, database applications were built directly on top of file systems
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation —multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become “buried”in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
Instances and Schemas
Similar to types and variables in programming languages
Schema–the logical structure of the database
Example: The database consists of information about a set of customers and accounts and the relationship between them)
Analogous to type information of a variable in a program
Physical schema: database design at the physical level
Logical schema: database design at the logical level
Instance–the actual content of the database at a particular point in time
Analogous to the value of a variable
Physical Data Independence–the ability to modify the physical schema without changing the logical schema
Applications depend on the logical schema
In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.
Transaction Management
A transactionis a collection of operations that performs a single logical function in a database application
Transaction-management componentensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.
Concurrency-control managercontrols the interaction among the concurrent transactions, to ensure the consistency of the database.