1, data
Data is a reflection and record of objective things, and it is a physical symbol used to carry information. Data is not the same as numbers. Data includes two types, numerical data and non-numerical data.
2. Information
Information refers to meaningful data, that is, meaningful descriptions defined on data.
3. Data processing
Data processing is the process of converting data into information. Data processing includes a series of activities such as data collection, sorting, storage, processing, classification, maintenance, classification, retrieval and transmission.
4. Database database
Database is the core of database system and the managed object.
5. Database management system
The database management system is responsible for managing and maintaining the database. It is the main software system of database system and management department. It realizes data storage and management with the help of operating system.
Generally speaking, a database management system should include the following functions.
Data Definition Language (DDL): used to describe and define all kinds of data in the database and their relationships.
Data Management Language (DML): used to insert, query, modify and delete data in the database.
Data Control Language (DCL): used for system control, data integrity control and concurrency control.
6. Database system
Database system is actually an application system, which consists of database, database management system, user and computer system.
A database is an object operated by a database system.
Database management system is a software system that database system is responsible for managing data.
Users are people who use the database. Users in a database system are end users, application designers and database administrators.
Computer system refers to the software and hardware resources for storing database and executing DBMS, such as operating system and disk, I/O channel, etc.
1. Database definition: A database is an organized collection of a large amount of data stored in a computer for a long time and can be enjoyed. The data in the database is organized, described and stored according to a certain data model, with less redundancy, high data independence and easy expansion, which can be enjoyed by all kinds of users. 2. The development of database management technology has experienced three stages: manual management stage, file system stage and database system stage. 3.DBMS (Database Management System) is a layer of data management software located between users and operating systems. Main functions: 1, data definition function. 2. Organization, storage and management of data. 3. Data operation function. 4. Transaction management and execution management of database. 5. Establishment and maintenance of database. 6. Other functions. 4. What is a data model and its elements? (Design Question): Data model is a tool to abstract the real world in the database and a formal framework to provide information representation and operation means in the database. Generally speaking, a data model is a collection of strictly defined concepts. These concepts accurately describe the static characteristics, dynamic characteristics and integrity constraints of the system. Therefore, data model usually consists of three parts: data structure, data operation and integrity constraint. (1) data structure: it is a collection of object types studied and a description of the static characteristics of the system. (2) Data operation: refers to the set of operations allowed by instances (values) of various objects (types) in the database, including operations and related operation rules, and describes the dynamic characteristics of the system. (3) Data constraint: It is a set of integrity rules, which are the constraints and dependence rules of data and their relationships in a given data model, and are used to limit the state and state changes of the database that conform to the data model to ensure the correctness, validity and compatibility of the data. The most commonly used data models: hierarchical model, grid model, relational model, regional object model and object-relational model. 5. What are the commonly used data models (mainly logical models), what are their characteristics and data structures? A: Data models can be divided into two categories: the first category is conceptual model, also known as information model, which models data and information according to users' views and is mainly used for database design. The second category is logical model and physical model. Logical models mainly include hierarchical model, hierarchical model, relational model, object-oriented model and object-relational model. It models data from the perspective of computer system and is mainly used for the implementation of DBMS. Physical model is the lowest abstraction of data, which describes the representation and access methods of data in the system, as well as the storage and access methods on disk or tape, and is oriented to computer systems. The task of database management system is to realize physical model. Database designers should understand and choose physical vinegar, and ordinary users don't have to consider the details of physical level. The data structure characteristics of hierarchical data model are as follows: First, only one node has no parent node, and this node is called root node. Second, other nodes besides the root have one and only one parent node. Advantages: 1 The hierarchical data structure is relatively simple and clear. 2. The query efficiency of hierarchical database is high. 3. The hierarchical data model provides good integrity support. The main disadvantages are: 1. In the real world, many connections are non-hierarchical, such as many-to-many connections between nodes. 2. A node has multiple parent nodes, and so on. The hierarchical model is clumsy and can only be solved by introducing redundant data or establishing unnatural data structures. There are many restrictions on insert and delete operations, so the writing of applications is more complicated. 3. The query child node must go through the parent node. 4. Due to the tight structure, hierarchical commands tend to be stylized. It can be seen that the hierarchical model describes one-to-many departments naturally, intuitively and easily, which is the outstanding advantage of hierarchical database. Mesh model: function: 1. Multiple nodes without a parent node are allowed. 2. A node can have multiple parent nodes. The advantages of grid data model are: 1. It can describe the real world more directly, for example, a node can have multiple parent nodes. intersection
There can be many kinds of repetition between them. 2. It has good performance and high access efficiency. The main disadvantages are: 1. The structure is complex, and with the expansion of the application environment, the structure of the database becomes more and more complex, which is not conducive to the end user to master. 2. DDL and DML of grid model are complicated and embedded in high-level languages, so it is not easy for users to master and use them. The relational data model has the following advantages: 1. Relational model is different from non-relational model, which is based on strict mathematical concepts. 2. The concept of relational model is simple. 3. The access path of relational model is transparent to users, so it has higher data independence, better security and confidentiality, and simplifies the work of programmers and the establishment of database development. The main disadvantage is that the query efficiency is often not as good as that of the non-relational data model, because the access path is clear. Therefore, in order to improve the performance, the database management system must optimize the user's query request. Therefore, it is more difficult to develop DBMS, but users don't have to consider the optimization technical details inside these systems. 6. What are the definitions of three-level architecture, external mode, mode and internal mode? Schema, also known as logical schema, is a description of the logical structure and characteristics of all data in the database, and it is a public data view for all users. External mode, also known as sub-mode or user mode, is a description of the logical structure and characteristics of regional data that database users can see and use, and a logical representation of data related to an application in the data view of database users. Internal schema, also known as storage schema, is a database with only one internal schema. It is a description of the physical structure and storage mode of data and a representation of data in the database. 7. Secondary image and secondary independence are called physical independence and logical independence. When the schema changes, the database administrator will change each external schema and the image of the schema accordingly, so that the external schema remains unchanged. The application program is written according to the external mode of data, so the application program does not need to be modified, which ensures the logical independence of data and programs, which is referred to as the logical independence of data for short. When the storage structure of the database changes, the database administrator can make corresponding changes to the schema and internal schema image to keep the schema unchanged, so that the application does not need to change. It ensures the physical independence of data and programs, referred to as the physical independence of data. 8. A database system generally consists of a database, a database management system (and its development tools), an application system and a database administrator. 9. Relationship integrity (entity integrity, referential integrity and user-defined integrity) consists of three parts, of which the first two parts are automatically supported by the system. What are the three main functions of DBMS integrity control subsystem? : Provides a mechanism for defining integrity constraints, provides a method for integrity checking, and handles breach of contract. Definition of 16. SQL structured query language is the standard language of relational database, and it is a universal and powerful relational database language. Classification (interactive and embedded) 17. The role of group by and having clauses. Concept of view: A view is a table derived from one or several basic tables. And related operations: define view, query view and update view. View updated operations: insert, delete and modify. 22. Definition of database normalization method function dependence What is 1NF2NF3NF BCNF definition: The relationship in a relational database must meet certain requirements, and different normalization is what meets different requirements. What meets the minimum requirements is called the first normalization, or 1NF for short. What meets further requirements in the first normalization is the second normalization, and so on. The relationship between various normalization is 5nf (4nf (bcnf (3nf (2nf (1nf)). 25. Several stages of database design, common methods and brief contents of each stage: six stages: demand analysis, conceptual structure design, Luo Zhi structure design, physical design, database implementation, database implementation and maintenance. 28. The concept of transaction? What are the basic attributes of a transaction? Mit roll back meaning: a transaction is a user-defined database operation sequence, which is an inseparable unit, either completed completely or not. Four characteristics: atomicity, consistency, isolation and persistence. Commit (all operations to commit the transaction) rollback (Rollback: There is some fault during the execution of the transaction, and the transaction cannot continue. All completed database operations in the transaction are cancelled and rolled back to the state at the beginning of the transaction. 29. What is the recoverability of a database system? The database management system has the function of restoring the database from an error state to a known correct state, which is the recoverability of the database system. Database failure types: internal transaction failure, system failure (soft failure), media failure (hard failure) and computer virus. 30. What problems may arise without concurrency control? The concurrent operation of multiple transactions on the database may lead to the destruction of the ACID characteristics of the transactions. How to solve (3): 1, lost revision 2, unrepeatable reading 3, reading "dirty" data. 3 1. Three-level blockade agreement? What problems can be solved? First-level blocking protocol: transaction T must add X lock to data R before modification, and will not be released until the end of the transaction. Transaction ending includes normal ending (commit) and abnormal ending (rollback). In the first-level blocking protocol, if the read data is not modified, there is no need to lock it, which can prevent the modification from being lost. Two-level blocking protocol: based on the first-level blocking protocol, transaction T is added. Before reading data R, an S lock must be added to data R, and then the S lock is released after reading. In the two-level blocking protocol, because the S lock can be released after reading the data, it cannot be guaranteed to be read repeatedly. Three-level blocking protocol: one-level blocking protocol plus transaction T must add S lock to data R before reading it, and will not be released until the end of the transaction. The three-level blocking protocol not only prevents the loss, modification and non-reading of "dirty" materials, but also further prevents the non-repetition of reading. The main differences between the above three-level protocols are: what operation needs to apply for blocking and when to release the lock. What three measures are generally taken? What about insertion? What about deleting? : 1, refused to execute (this operation is not allowed), 2, cascaded operation (when deleting or modifying one tuple of the referenced table leads to inconsistency with the referenced table, all tuples in the referenced table will be deleted or modified), 3, set to null value (when deleting or modifying one tuple of the referenced table leads to inconsistency, the corresponding properties of all tuples in the referenced table will be set. 38. What is the impact of views on database security? : 1, viewing can simplify users' operations, 2. eyesight enables users to view the same data from all angles, 3. Viewing provides a certain degree of logical independence for reconstructing the database, 4. Viewing can provide security protection for confidential data, and 5. Proper use of viewing can express queries more clearly. Database: A large collection of data stored in a computer, which is permanently stored, organized and enjoyed. Development stage of data management technology: 1. Manual management stage: data is not stored, data is managed, data is not enjoyed, and data is not independent. 2. File system stage: data can be stored for a long time and managed by the file system; Data * * * has poor enjoyment, great redundancy and poor data independence. 3. Database system stage: Database management system appears. Characteristics of database system: data structure (essential difference); Data * * * has high enjoyment, low redundancy and easy expansion; High data independence; The data is managed and controlled by the database management system. Database management system: 1. Definition: DBMS is a layer of data management software between users and operating system. 2. Function: data definition function; Organization, storage and management of data; Data operation function; Transaction management and execution management of database; Database establishment and maintenance functions; Communication function, data conversion function, mutual access and interoperability function. Database system: 1. Concept: DBS refers to the system after introducing the database into the computer system. 2. Composition: generally composed of database, database management system, application system and database administrator. 3. Classification: centralized, C/S, parallel and decentralized. Data model: 1. Definition: the abstraction of data characteristics in the real world. 2. Composition, three elements: data structure, data operation and data integrity constraint. The two data models are 1) conceptual model 2) logical model and physical model. Data structure: describes the components of the database and the links between objects, mainly describing the objects related to the types, contents and attributes of objects and the links between data. Common data model: 1. Hierarchical model, using tree structure to represent various entities and the relationship between entities. 2. Grid model allows multiple nodes to have no parent nodes, and allows a node to have multiple parent nodes. 3. Relational model, including single data structure
What is the conceptual structure of database? On its characteristics and design strategy. Database system, also known as DBS, is a system composed of database and its management software. Commonly used systems are: Oracle, DB2, SQL Server Aess, etc. Its characteristics can be summarized as: providing users with an easy-to-use user interface and safely managing and maintaining data and their relationships.
Database conceptual structure design E-R diagram what is your database conceptual structure! I can help you design the E-R diagram!
What are the conceptual structure, logical structure and physical structure of a database? How is the database designed? How to consider the security of the system? The basic concept of database system: in fact, it is a symbolic record that describes things. Characteristics of data: there are certain structures, types and values, such as integer, real and character. The value of the data gives a value that conforms to the prototype, such as integer value 15. Database: A collection of data with a unified structure and stored in a unified storage medium. It is the integration of various application data and can be enjoyed by various applications. The data stored in the database is stored according to the data pattern provided by the data, which has the characteristics of integration and * * * *. Database management system: a kind of system software, which is responsible for data organization, data operation, data maintenance, control and protection and data service in the database, and is the core of the database. Database management system function: (1) data schema definition: that is, to build its data framework for the database; (2) Physical construction of data access: providing effective access methods and means for physical access and construction of data patterns; (3) Data manipulation: it provides convenience for users to use the data in the database, such as query, insertion, modification and deletion, as well as simple arithmetic operation and statistics; (4) Definition and inspection of data integrity and security; (5) Concurrent control and fault recovery of database; (6) Data services: such as replication, transfer, reorganization, efficiency monitoring and analysis. In order to complete the above six functions, the database management system provides the following data languages: (1) data definition language: it is responsible for the schema definition and physical access construction of data; (2) Data operation language: responsible for data operation, such as query, addition, deletion and modification; (3) Data control language: responsible for the definition and inspection of data integrity and security, concurrency control, fault recovery, etc. According to its usage, data language has two structural forms: interactive command (also called self-contained or autonomous language) host language (generally embedded in some host languages). Database administrator: a professional administrator who plans, designs, maintains and monitors databases. Database system: an executive entity consisting of five parts: database (data), database management system (software), database administrator (personnel), hardware platform (hardware) and software platform (software). Database application system: consists of database system, application software and application interface. File system stage: provides simple data sharing and data management capabilities, but cannot provide complete and unified management and data sharing capabilities. Hierarchical database and network database system stage: provide strong support for data unification and * * * sharing. The basic characteristics of the database system in the stage of relational database system are: data integration, high data enjoying low redundancy, data independence (physical independence and logical independence), and unified management and control of data. Three-level mode of database system: (1) Conceptual mode: describes the logical structure of domain-wide data in database system, and all users can view the data publicly; (2) External mode: also called sub-mode and user mode. Is the user's data view, that is, the data pattern that the user sees; (3) Internal mode: also called physical mode, which gives the physical storage structure and physical access method of the database. Two-level mapping of database system: (1) mapping from conceptual schema to internal schema; (2) Mapping from external pattern to conceptual pattern. 4.2 Data model The concept of data model is the abstraction of data characteristics, which describes the static characteristics, dynamic behaviors and constraints of the system from an abstract level and provides an abstract framework for the information table and operation of the database system. The data structure, data operation and data constraints are described. The basic concept of E-R model (1) entity: things in the real world; (2) Attribute: the characteristics of things; (3) Connection: the relationship between things in the real world. Entity sets have one-to-one, one-to-many and many-to-many relationships. The relationship between the three basic concepts of E-R model: entity is the basic unit in the conceptual world, and attribute has attribute domain, and each entity can take the value in the attribute domain. All the attribute values of an entity are called tuples. Graphical representation of E-R model: (1) entity set representation; (2) Attribute table method; (3) contact representation. The basic structure of hierarchical model is tree structure, which has the following characteristics: (1) Each tree has only one parent node, which is called root; (2) All nodes except the root in the tree have only one parent node. From the perspective of graph theory, the grid model is an undirected graph without any conditions. The relational model is represented by a two-dimensional table, which consists of a table frame and a table tuple. A two-dimensional table is a relationship. The smallest attribute that can uniquely identify a tuple in a two-dimensional table is called a key or code. Select a key from all candidate keys as the user's primary key. An attribute in Table A is the key of Table B, then this attribute set is called the foreign key or foreign key code of A. Data constraint in the relationship: (1) entity integrity constraint: the attribute value in the primary key of the constraint relationship cannot be empty; (2) referential completeness constraint: it is the basic constraint between relationships; (3) User-defined integrity constraint: it reflects the semantic requirements of data in specific applications. 4.3 A characteristic of relational algebra relational database system is that it is based on data theory, and there are many data theories that can represent the data operation of relational model, among which relational algebra and relational calculus are the most famous. Basic operations of relational model: (1) Insert (2) Delete (3) Modify (4) Query (including projection, selection and cartesian product operation) 4.4 Database design and management Database design is the core of data application. Two methods of database design: (1) data-oriented: giving priority to information demand and giving consideration to processing demand; (2) Process-oriented: give priority to handling requirements and give consideration to information requirements. Life cycle of database: requirement analysis stage, conceptual design stage, logical design stage, physical design stage, coding stage, testing stage, implementation stage and further modification stage. Structured method and object-oriented methods are commonly used in requirements analysis. Structural analysis (SA) method analyzes the system through top-down and layer-by-layer decomposition. Use data flow diagram to express the relationship between data and processing. For database design, data dictionary is the main result of detailed data collection and data analysis. A data dictionary is a collection of various data descriptions, including five parts: data item, data structure, data flow (either data item or data structure), data storage and processing. The purpose of database conceptual design is to analyze the internal semantic relations of data. There are two design methods (1) centralized pattern design method (suitable for small or uncomplicated units or departments); (2) Review the integrated design method. Design method: E-R model and view integration. Generally, inspection design has three design sequences: top-down, bottom-up and inside-out. View several conflicts of integration: naming conflict, concept conflict, domain conflict and constraint conflict. Relational view design: The design of relational view is also called external pattern design. The main functions of relational view are: (1) providing logical independence of data; (2) It can meet the different needs of users for data; (3) It has a certain data security function. The main goal of database physical design is to adjust the internal physical structure of data and choose a reasonable access path, so as to improve the access speed of database and make effective use of storage space. Generally speaking, the contents left for users to participate in physical design in RDBMS are index design, integrated cluster design and partition slot design. Contents of database management: (1) database establishment; (2) adjustment of database; (3) Reorganization of the database; (4) database security and integrity control; (5) database fault recovery; (6) Database monitoring.
Conceptual structure design in database design refers to the overall development of a database and needs to be designed. The main steps are demand analysis, conceptual structure design, logical structure design, physical structure design, database implementation, database implementation and maintenance. Physical structure design is one of them.
The physical structure design of database is to design an efficient and realizable physical data structure with better data storage structure, data access path, reasonable data storage location and storage distribution by using the methods and technologies provided by DBMS. Generally speaking, it is to design a corresponding and optimized physical structure for the designed logical structure, and the designed physical structure can store data.
What is the concept of database? Database: It is a tool for storing and managing data, and the database is also developed from the level of writing files. At that time, there was no concept of database, and it was found that:1> Everyone has to write a program or method to read and write files, that is, the interface is different; The management of 2> file system becomes a problem, especially when there are many files; 3> cannot reflect the relationship between files in the file system; 4> cannot reflect the relationship between files in the file system; At least have the above four points, and then gradually refine the concept of a database (such as the development interface ODBC and other general development interfaces), starting from the non-relational database (now name: nosql) layer->; Figure->; Relational type->; Relationship-oriented object mixing->; Object-oriented database ... theory and products are developed according to this route ... Henan Xinhua Net Road Operation Association will answer for you!
The difference between conceptual structure design and logical structure design of database logical structure design. According to the established conceptual data model and the data model characteristics of database management system software, according to certain conversion rules.
Convert the conceptual model into a logical data model acceptable to this database management system.
Different database management systems provide different logical data models, such as hierarchical model, network model, relational model and so on.