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The database system is a system by the database management software. It is developed to meet the construction needs of data processing and a data processing core institutions. This is an actual running store and maintain software systems to provide data and application system, a set of storage media processing object management system. It usually consists of software, databases and data administrators. The software includes the operating system, the host language, tools and database management systems. Unified database managed by the database management system, insert, modify, and retrieve data through the database management system. The data administrator is responsible for the creation, monitoring and maintenance of the entire database, the data can be any right to use. Database administrator of a higher level of business, more senior officials. Personal significance database system refers to a particular database management system software, and use it to set up the database; This means that it is the subject of research, development, establishment, maintenance, and application of the theory of database systems, methods, technical disciplines. In this sense, the database system is the branch software is an important field of study, and is usually referred to as a database field. Database system developed to meet the need of data processing and a data processing core institutions. The high-speed processing and high-capacity computer memory conditions, and automated data management. Database research in three areas of computer applications, system software, and application of theory, including research and development of new systems, the new system has brought a new theoretical research, theoretical research plays a guiding role in the first two areas. The emergence of the database system is a milestone in computer applications, computer applications from the main scientific computing to data processing, computer can used a variety of industries, and even families. Application before the file system, it can deal with persistent data, but the file system does not provide a quick access to the part of any data, and increase the amount of data is crucial. In order to achieve fast access to any data it is necessary to study a lot of optimization techniques. These optimization techniques are typically very complex, difficult to reach the average user, so the user of the system software (database management system) can be used is a simple and easy to use the language of the database. Due to the completion of the database management system of the operation of the database, the database may be independent of the presence of a particular application, so that the database can be shared by multiple users. Thus, the independent and shared data is an important feature of the database system. Data sharing to save a lot of manpower and resources, and to lay the basis of a database system widely used. The emergence of database systems to let ordinary users daily data can easily be stored in a computer and access them quickly when needed, such computer research institutions for all walks of life into the home. Database by factors of three main types:
(1) computer hardware
The database system of the material basis of the computer hardware, hardware resources are stored in the database and run a database management system, including the hosts, storage devices, input and output devices, computer network environment.
(2) Computer software
Database system software, including operating systems, database management systems and database applications.
The database management system is a core database software system. It provides a data definition, data processing, database management, database creation and maintenance, as well as communications and other functions. DBMS provides a unified management and control functions of the database data resources, data users, applications, and databases are isolated, the core of the database system, the function of the advantage of the strength of the main performance indicators to measure the database system. DBMS must be run on the system platform, operating system and system software support. Strength and system of DBMS functionality changes in large systems more powerful than the whole, more powerful and less in small systems. The NCRE two, access, SQL Server, Oracle, Sybase and other database management system is more popular.
(3) The database system personnel
Database application developers and database administrator (DBA). The end-user through the user interface of the application system using the database staff, and they usually do not know much about the knowledge of the database. Database application systems development, systems analysts, system designers and programmers.Compatible with systems analyst responsible for analyzing application system, user, and database administrators involved in system analysis, system designers responsible for the application of the system design and database design; programmers coded according to the design requirements. The database administrator is a group of data management institutions, they are responsible for the overall control and maintenance of the entire database system in order to ensure the normal operation of the database system.
Conclusion of question 1
In conclusion, we can get the results, the database is very helpful for computer users. Since the database data is very fast and complete, allowing users to easily understand and facilitate the process. So the primary key and foreign key in the database are very useful
Primary key: primary key in the RDBMS is inevitable, each record in the data table only a combination of text, or text is known as the master code (primary key). Primary key primary key that uniquely identifies each record in a table, but just one part of its role, the main role of the other tables in the recording and storage of data. . At this point, the difference between the primary key is a simple pointer table each record. Therefore, the value of the primary key of the user does not make sense, and it must be taken into account nothing special value. Can also generate DBMS (such as a globally unique identifier, or GUID, in Microsoft SQL Server). The primary key can be combined by a single property or multiple properties.
For general inquiries faster, because the primary key index of the duplicate rows, the above is not allowed in a relational database, the only representative of the primary key only primary key of the row, is mainly used for data constraints. Insert data in the primary key column can not be empty, if empty SQL error. A primary key is a unique primary key to identify a record, if your primary key record SF110 further inserted inside the SF110 record SQL error will be a table. Primary keys are generally chosen do a record field, for example, there is now a student table "inside" student card "Student Name" student "
Of course, "as the basis of the number of students of the primary key principles.
There is a principle, which is not often modify the primary key field. Student cards on the table, and certainly will not be modified, it is also more in line.
The primary key cannot just set, there is a primary key of the table is the best, because it is a good habit, if you do not set the primary key in the SQL Enterprise Manager cannot add a delete operation. Can protect one or more columns in the primary key of the table, each column of data to the end of the joint action of the primary key constraint NOT NULL constraint. NOT NULL constraint and a unique constraint combination will ensure that the primary key that uniquely identifies each row. The only constraint, primary key, enhanced B-tree index. Create primary key constraint using the CREATE TABLE statement to create the table, if the table has been created, you can use the ALTER TABLE statement. In the case of the relational database, the foreign key referential constraints, the two tables.
Foreign key field in a relational table that matches the candidate key of another table. Foreign key can be used to cross-reference table.
For example, in the example below, there is a link to the Company table. The Company table is a link in the parent table. Contact table is the child: The Contact table company_id games company contact.
Identify one or a group of foreign key (for reference only), refers to one or more columns in the table column in another table (reference). Columns in the referenced table must refer to the referenced table's primary key or other key columns. Line column values â€‹â€‹must appear in a row in the referenced table. Therefore, in a row in the referenced table does not contain a value, the referenced table does not exist (except potentially NULL). This can refer to link information together, it is an important part of database normalization. Multiple lines the reference table, the table may be referenced in the same row. In most cases, it reflects a lot of (parent table or table) (sub-tables or references to the relationship between the tables).
Reference and reference table can be the same form, that is, at the same table foreign key references. This foreign key is referred to as a self-referential foreign key or recursive SQL.
A table can have multiple foreign keys, each foreign key can have different reference table. Each foreign key independent database system. Therefore, the relationship between cascade table, you can use the foreign key created.
Incorrect foreign key / primary key relationship or non-execution of these relationships are often the source of many database and data modeling problems.
Foreign key that matches the value of the primary key in the value of an attribute field or column in the table foreign key relationships. For example, if there are two tables, a table has a primary key. The primary key is a unique table column does not appear twice in the same column. The second table's primary key and foreign key. Foreign key to the primary key of the table. Is completely different from the first table, the second table contains a primary key is unique. Once we understand this concept, we have what is called the referential integrity. Referential integrity, foreign key contains a value, the value refers to an existing line (first line) relational tables. If you are creating a relational database referential integrity. For example, if we have a list of the tag's ID number, list figures in the table, one with exactly the same label and the same number is just a different location.
Conclusion of question 1
In conclusion, we can get the database information, databases, computer users have a great deal of help. Since the database to display the data is very easy to understand and easy, users can quickly update and storage. Primary keys and foreign keys in the database is very useful for users.
The relational database is a collection of items of the organization as a group of formal data table for access or restructuring in many different ways, without having to re-organization of the database table data. The relational database is a formal description of the table's data collection can easily access the organization's data entry. Create a relational database relational model. The software used in a relational database is called a relational database management system (RDBMS). A relational database to store data than other models, hierarchical database model or network model. In 1970, EF Codd of IBM invented the relational database. The standard user and application program interface to relational databases, Structured Query Language (SQL). SQL statements for interactive query and report of the data collected from the relational database information.
In addition to relatively easy to create and access a relational database has the important advantage of easy expansion. Create a new data category can be added after the original database, without the need to modify existing applications.
A relational database table, which contains a set of data to install into predefined categories. Each table (also sometimes called relationship) contains one or more columns of data categories. Each row contains a unique instance of the data columns defined categories. Financial records, manufacturing and logistics information, the storage of personal data and information for the new database, relational database, a relational database management system, has become a major choice. The relational database is often replaced traditional hierarchical databases and network databases, because they are easier to understand and use, even if they are very inefficient. As computer power increases, the inefficiency of the relational database, in earlier times, they unrealistic and has exceeded its ease of use. However, relational databases, object database, which describes in trying to solve the challenges in a relational database, object-relational impedance mismatch and XML database. Three major commercial relational database vendors Oracle, Microsoft and IBM.  The three leading open source implementation MySQL, Postgre SQL's SQLite Amazon Relational Database Service is a database MySQL and Oracle database engine as a service.
The object database (also object-oriented database management system) is a database management system, in the system, the information that the form of the object in the object-oriented programming. With different relational databases and object databases belonging to a wider range of database management systems.
Be considered since the early 1980s and 1990s, object database. The main purpose of the object database in the field of object-oriented. When database capabilities combined with the ability to object-oriented programming language, the result is an object-oriented database management system (OODBMS). OODBMS allows programmers to develop object-oriented products store object, copy, or modify an existing object, make a new object-oriented database objects. Due to the integration of the database programming language, programmers can be in an environment consistent because the OODBMS and representatives of the programming language will use the same model. Relational database management system project, by way of contrast, the clearer division of lab or between maintain the database model and application.
With the use of network technology to increase the implementation of Intranet and Extranet, companies have a vested interest in OODBMS, to show the complexity of the data. The company has been designed to store data as objects using the DBMS provides an advantage for multimedia presentations or organizations, the use of computer-aided design (CAD).
Object-oriented databases are designed to work as well as object-oriented programming languages, such as Delphi, Ruby, Python Perl, Java, C #, Visual Basic.NET, Ç purpose of, Ç and Smalltalk Other people have their own programming language. The OODBMSs use exactly the same model, object-oriented programming language. Object database management system in the mid-1970s, the predecessor of the early object graph structure with internal database management support. The term "object-oriented database system" first appeared in 1985.  research projects, including the famous the Encore-Ob/Server (Brown University) EXODUS (Wisconsin - Madison University), IRIS (HP), the ODE (Bell Labs), ORION (Microelectronics and Computer Technology Corporation or MCC) , Vodak (GMD-IPSI) and the spirit of the times (Texas Instruments). The Orion Project has published papers than any other efforts. Won gold MCC compiled in a book published by the MIT Press in the best of those files. 
The early days of commercial products, including the in the gem (Service Logic, change the name of the Gem Stone system), GBASE (Graphed), the bottom of the value (ontology). The early 1990s to the mid-20th century to see more commercial products to enter the market. These measures include ITASCA (Itasca systems), Jasmine (Fujitsu sales by Computer Associates), Ma Ortiz (Matisse's software), objectivity / DB (the objectivity company), Object Store (Progress software company, the acquisition EXCELON It would have been the object of design), of ONTOS (ONTOS company name changed ontology), O 2  (O 2 technology, merger of several companies acquired by Informix, and the acquisition of IBM) the poet (Fast Objects, from Versant acquired the poet software) Versant object-oriented database (Versant Corporation) VOSS (logic Arts) and Jade (jade software company). Some of these products are still in the market, has joined a new open-source and commercial products such as Inter Systems Cache.
Persistent concept of object database management systems, object-oriented programming language. Early commercial products, integrated gem of languages â€‹â€‹(Smalltalk) GBASE (LISP), the bottom of the value (COP) and Voss (virtual the Smalltalk object storage system). The 1990s, most of the time, the C + + the dominant commercial object database management market. Java vendors join in the late 1990s, recently, C #.
Beginning in 2004, the object database to see the emergence of a second growth of open source object database, a wide range of affordable and easy-to-use, because they are completely written in object-oriented programming language Smalltalk, Java or C #, as Versant's db4o (db4objects) DTS/S1 from obsidian dynamics and the Perst (McObject company), under dual open source and commercial licenses.Object-relational database (ORD), or object - relational database relational database management system (ORDBMS), is a database management system (DBMS) to similar, but with an object-oriented database model: objects, classes, inheritance is a direct database schema (schema) query language support. In addition, appropriate relations system, it supports extended data model uses custom data types and methods. Object - relational database, can be said to provide a middle ground between relational databases and object-oriented database (OODBMS). Object - relational database, this approach is essentially relational database data resides in the database, and the collective in the query language query operation, and in the other extreme is the database software essentially is a persistent Object Storage OODBM written in an object oriented programming language, is used to store and retrieve objects programming API, with little or no specific query support. The basic goal of object relational database is to bridge the relational database and object-oriented model techniques, such as the gap between the JAVA programming language used, C, Visual Basic. NET or C #. However, a more popular alternative to achieve such a bridge is some form of object - relational mapping (ORM) software using standard relational database system. Allow the effective management of the data from a limited set of data types (as defined in the relevant language standard) and traditional RDBMS and SQL DBMS products focus on an object - relational DBMS software developers to their types and methods applicable in them to the DBMS.
ORDBMS (ODBMS, or OODBMS etc.) integrates an object-oriented programming language. ORDBMS characteristics
(1) The complexity of the data,
(2) the type of inheritance,
(3) the object's behaviour. Preliminary architecture defined by the user-defined type (UDT) on the basis of complex data, most of the SQL ORDBMSs. Complex hierarchy of data provides an additional attribute, type inheritance. That is, the type of structure can contain sub-reuse all of its properties, and contains a specific sub-type of additional properties. Another advantage is that the behaviour of the object is the access to the related program objects. The object of this program can store and transport database processing, they usually named persistent objects. In a database, the object of an ongoing plan is all relations object identifier (OID). All of these issues can be resolved in an appropriate relationship, but the SQL standard and its implementation to impose arbitrary restrictions and additional complexity
The behavior of objects in object-oriented programming (OOP) is by method (objective function). A name difference is that their types and their parameters (signature) connected object type. Call this polymorphism principles of object-oriented programming language, simply defined as "an interface to achieve. Other object-oriented principle of inheritance and packaging methods and properties. Methods inherited class inheritance. Encapsulation in object-oriented, for example, is a visibility announced by public, private and protected modifiers.
Conclusion of question 2
In conclusion, the three relational database, face as databases, relational databases and object database has its own usefulness. Brought many benefits and convenience for the database. We should give full play to their purpose and role in the database.â€ƒ