Glossary
- Database: The database is in the computer, organized, large amounts of data can be shared set of long-term storage. Database Features: data model data according to a certain organization, storage and described; may be a variety of users to share. Redundancy is small; higher data independence: easy to expand
- DBMS: database management system (DBMS) is a data management software layer positioned between the user and the operating system. Organize and store data for scientific and efficient acquisition and maintenance data.
- Data Independence: struggling between data and programs, including logical and physical independence of independence. Independence logic: when the mode is changed, the external mode for the corresponding mode map changes can be made outside the mode remains unchanged, thereby having to modify the application. Physical independence: When the storage structure of the database changes, the effect on the action of the respective mode change mode, mode can remain unchanged, so that the program remains unchanged.
- Integrity: accuracy and compatibility, to prevent undesirable semantic data into the database.
- Transaction, commit, rollback: A transaction is a sequence of user-defined database operations, these operations are either full or not full to do, is not a division of the workplace. Commit the transaction ends normally. Rollback refers to a failure, to undo a state before execution.
Short answer
- Brief database three modes, two images
three modes can be classified outside the pattern, and the pattern mode. Model is an abstraction of the real world, is a global logic structure, specifically, is the basic concept of medium-sized table. External mode is the local logic embodied structure can be understood as a subset of the model. The model is a description of the inside of the database system and the physical structure of the storage structure.
Mode image can be divided into two outer mode map, the mode map mode. External mode map mode means that when the logical structure of the system is changed, without changing the external mode may, thus ensuring the independence of a certain logic. The mode map mode means that when the logical structure of the system changes, the physical structure and the storage structure is no need to change, thus ensuring a high degree of physical independence. - It features database system for managing data?
(1) and structured data associated with each set: describe not only the data itself, also describes the link between the data.
(2) data sharing high and low redundancy.
Independence (3) High data: two three image mode ensures a high degree of independence and physical independence of a certain logic.
(4) have a unified data management and control functions: security, integrity, concurrency control and recovery of data. - The main function of the DBMS
definition function (1) data, the DBMS provided DDL language to define the structure of the database, such as: CRETATE, DROP, ALTER
operating functions (2) data, DBMS provided DML language to achieve the basic operation of the database, such as: the SELECT, DELETE, INSET ... ...
(3) operation and management functions of the database, mainly in four areas: security control, data integrity control data, concurrent multi-user control, data recovery
(4) database establishment and maintenance - DBMS data stored in the procedure
(1) using a specific user data manipulation language sent to the DBMS access request
(2) DBMS receives the request and the request is converted to machine code instructions
(. 3) DBMS successively check the images and patterns, not meet the immediate return
(4) DBMS perform the necessary access operation to the database
(5) to get results from operations
(6) to do some processing results, such as: format conversion.
(7) returns to the user - Description of data processing and data abstraction model
the real world by understanding abstract concepts of the world, the concept of the world to get the data model supported by the DBMS based on the conversion.
Data model can be divided into a conceptual model, a logic model (or data model), physical model
(1) is a conceptual model of reality an abstract model may be understood as requirements ER diagram
(2) in the logical model is a conceptual model of based on two abstractions, can be divided into: hierarchical model, the relational model, the mesh model, object-oriented model
(3) the underlying physical model is the most abstract. - Constituent elements of the data model
(1) data structures including data links between the type, content, properties, as well as data.
(2) data operations, such as additions and deletions
(3) Integrity constraints
entity integrity: Main attribute value relationship is not and can not have the same value Null
referential integrity: foreign key relationship must be a primary key in another relation rMS, or NULL
custom constraint: a user-defined data must satisfy the constraint - Summary of the structure of the database
(1) the data file
the data file is located data file database and database objects. A database can have one or more data files, one data file belongs to a database. When there are multiple data files, a file will be determined as the main data file, extension .mdf, this data file extension .ndf.
(2) the transaction log file
transaction log file used to record database update status, suffix .ldf, all operations will be recorded in the log file. A database can have one or more log files.
(3) file group
files group is a set of a plurality of data files integrally formed together. - System database which
Master database stores all system-level information for SQL Server
Model database, a template database stores all user databases and create a template Tempdb database
Msdb is a proxy service database
Tempdb is a database temporarily storing the
Resource database database system objects and user data.