Author: 咳嗽di小鱼 Date: October 18, 2011 Category: Sum Up
- Database: is a large and persistent collection of pieces of information organized in a way that facilitate efficient retrieval and modification.
- DBMS: is a program that manages details related to storage and access for a database.
- Schema: is a description of the data interface to the database.
- Instance: is a database that conforms to a given schema.
- Transaction: is an application-specified atomic and durable unit of work.
- View: is a relation in the external schema whose instance is determined by the instances of the relations in the conceptual schema.
- Trigger: is a procedure executed by the database in response to a change to the database instance
Three Level Schema Architecture
- External schema (view): visualized data
- Conceptual schema: logical structure
- Physical schema: file/storage devices
- Application access the data through an abstract data model provided by the DBMS, rather than direct access
- Physical: applications cant touch the storage stucture
- Logical: applications cant change the data organization
Four Transaction Properties
NoSQL据说就是要break these properties= =`IDK why...
- Atomic: once the transaction happens, it happened. No intermediate stage!
- Consistency: transaction follows the database consitences
- Isolated: concurrent transactions wont effect each other
- Durable: transaction results permanently
What DBMS do
- Remoce common code from applications
- Provide uniform access to data
- Guarantee data integrity
- manage concurrent access
- Protect against system failure
- Set access policies for data