Database Management(英文版)(ppt 25頁)

Database Management(英文版)內容提要：
A database consists of a file or a set of files. The information in these files may be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage, and each field typically contains information pertaining to one aspect or attribute of the entity described by the database. Using keywords and various sorting commands, users can rapidly search, rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregates of data.
一個數據庫由一個文件或文件集合組成。這些文件中的信息可分解成一個個記錄，每個記錄有一個或多個域。域是數據存儲的基本單位，每個域一般含有由數據庫描述的屬於實體的一個方麵或一個特性的信息。用戶使用鍵盤和各種排序命令，能夠快速查找、重排、分組並在查找的許多記錄中選擇相應的域，建立特定集上的報表。
Database records and files must be organized to allow retrieval of the information. Early systems were arranged sequentially (i.e., alphabetically, numerically, or chronologically); the development of direct-access storage devices made possible random access to data via indexes. Queries are the main way users retrieve database information. Typically, the user provides a string of characters, and the computer searches the database for a corresponding sequence and provides the source materials in which those characters appear. A user can request, for example, all records in which the content of the field for a person’s last name is the word Smith.
數據庫記錄和文件的組織必須確保能對信息進行檢索。早期的係統是順序組織的（如：字母順序、數字順序或時間順序）；直接訪問存儲設備的研製成功使得通過索引隨機訪問數據成為可能。用戶檢索數據庫信息的主要方法是query(查詢)。通常情況下，用戶提供一個字符串，計算機在數據庫中尋找相應的字符序列，並且給出字符串在何處出現。比如，用戶能夠在所有記錄中尋找所有last name域為Smith的記錄。

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