A database is a collection of data organized according to a data model and stored in secondary memory. This collection of data has the following characteristics: as far as possible without duplication, in order to optimize the way for a particular organization's multiple applications, its data structure is independent of the application using it, the data addition, deletion, modification and retrieval by a unified software management and control. From the history of development, the database is an advanced stage of data management, which is developed by the document management system.

The basic structure of a database is organized into three levels, reflecting three different perspectives from which to view the database.

(1) The physical data layer. It is the innermost layer of the database and is the collection of data actually stored on the physical storage device. These data are raw data, objects processed by the user, and consist of bit strings, characters, and words processed by instruction operations described by internal schemas.

(2) Conceptual data layer. It is the middle layer of the database and is the overall logical representation of the database. It points out the logical definition of each data and the logical connection between the data, and is a collection of stored records. It is concerned with the logical relationship between all the objects of the database, rather than their physical situation, is the database administrator's concept of the database.

(3) logical data layer. It is the database as seen and used by the user and represents a collection of data used by a particular user or users, i.e., a collection of logical records.

The links between the different layers of the database are transformed by mapping. Databases have the following main characteristics:

(1) Realization of data *** enjoyment. Data **** enjoyment includes all users can access the data in the database at the same time, but also includes users can use the database in a variety of ways through the interface and provide data **** enjoyment.

(2) Reduce data redundancy. Compared with the file system, because the database realizes data **** enjoyment, thus avoiding the users to create their own application files. It reduces a large amount of duplicate data, reduces data redundancy and maintains data consistency.

(3) Data independence. Data independence includes the logical structure of the database in the database and the application programs are independent of each other, but also includes changes in the physical structure of the data does not affect the logical structure of the data.

(4) data to achieve centralized control. Document management, data in a decentralized state, different users or the same user in different processing of their documents have no relationship. The use of databases can be centralized control and management of data, and through the data model represents the organization of various data and the link between the data.

(5) data consistency and maintainability to ensure data security and reliability. Mainly includes: ① security control: to prevent data loss, incorrect update and overstepping the right to use; ② integrity control: to ensure the correctness, validity and compatibility of the data; ③ concurrency control: so that in the same time period, allowing the realization of multiple accesses to the data, but also prevents abnormal interactions between the users; ④ fault discovery and recovery: by the database management system to provide a set of methods, which can be timely detection of faults and repair faults, thus preventing the destruction of data

You may be a beginner, put it this way, the database is to build a table, and then a table nailed together, it became a large pile of data, with the professional terminology, we call such a large pile of tables database.

Books a lot of ah, & lt; Introduction to the database & gt; this book is good, I have learned this book, although it is a little more than the present Lun, but while learning this book, and then look for a practical textbook, (I mean a special learning database a software book,) very beneficial.

I was talking about this book, while talking about <SQL server 2000>

SQL, MySQL, more suitable for learning the database at home,

ORCAL, more suitable for the company's applications

DEPHI, itself is not a database, but a database system, quite practical software, and the database system, the database system, the database system, the database system, the database system, the database system, the database system, the database system, and the database system, the database system, the database system, the database system, the database system, the database system, and the database software, the database system, the database system, and the database software, and the database software.

DEPHI, itself is not a database, but is a database system, quite practical software is very practical.

ACCESS, more suitable for the application of it, not quite suitable for the use of it to learn the database, because ACCESS generally do not use the language, and is oriented to the general user, that is to say, with a more convenient and practical,

I do not know, so that you can understand how much you are still looking for a book to learn about it,

Right, I forgot to say to you,"