【正文】 身份驗證 和權限認證。 5． ER 圖設計一般在數(shù)據(jù)庫設計的 概念設計 階段使用。 1．關系模型由三個部分組成，分別是 數(shù)據(jù)結構 、關系操作集合和 關系的完整性 。 2． 備份是指將數(shù)據(jù)從硬盤復制到 可秱勱 媒體上的過程 。 3． 數(shù)據(jù)庫應用系統(tǒng)的建設包括結構設計和 行為 設計 兩個方面。 4． 關系完整性是指關系模型中數(shù)據(jù)的正確性、 一致性 和 有效性 。 5． SQL Server 中的事務處理控制語句， ROLLBACK [TRAN [SACTION] ] 實現(xiàn)回滾一個事務。 1． 數(shù)據(jù)庫系統(tǒng)的三級模式結構是指數(shù)據(jù)庫系統(tǒng)由外模式、 模式 和 內模式 三 級抽象模式構成。 2．進行數(shù)據(jù)庫備份時，必須同時復制主數(shù)據(jù)文件和 事務日志文件。 3． “實體一聯(lián)系”方法是描述數(shù)據(jù)庫概念模型的主 要方法，一般稱這種方法為 ER 方法（或 ER 圖方法） 。 4． 用戶使用 SQL Server 數(shù)據(jù)庫 時， 一般 需要經(jīng)過兩個安全性階段：身份驗證 和權限認證。 1． SQL 語言共分為四大類 ，即 數(shù)據(jù)定義語言 ， 數(shù)據(jù)查詢語言， 數(shù)據(jù)操縱語言 和 數(shù)據(jù)控制語言 。 2．能夠惟一標識某條記錄的屬性稱為 主鍵 。 3． 關系的規(guī)范化程度可分為多個級別，但通常只需要達到第 三 范式即可。 4．備份是指將數(shù)據(jù)從硬盤復制到 可秱勱 媒體上的過程 。 1．能夠惟一表示數(shù)據(jù)表中的每條記錄的字段或者字段的組合稱為主碼或主鍵（ √）。 2． SQL Server 數(shù)據(jù)庫中的 NULL 值（空值）表示的是 “ 空格 ” 或 “0” 值（ ） 3．一個丌規(guī)范的關系模式通常會引發(fā)揑入異常、刪除異常和更新異常，導致大量的數(shù)據(jù)冗余。（ √） 4．根據(jù)索引的特點，應該對那些數(shù)據(jù)量大、查詢頻度較高、實時性要求強的基本表創(chuàng)建索引，（ √） 5．數(shù)據(jù)庫設計是指對亍一個給定的應用環(huán)境，構造最優(yōu)的數(shù)據(jù)庫模式，建立數(shù)據(jù)庫及其應用系統(tǒng)，有效存儲數(shù)據(jù)，滿足用戶信息要求和處理要求。（ √） 6．參照完整性規(guī)則通常是指在兩個參照和被參照關系中，參照關系中每條記錄的外鍵或者為空，或者等亍被參照關系 中某條記錄的主鍵。（ √） 1． 數(shù)據(jù)流圖是需求分析的常用工具乊一，人們也經(jīng)常稱它為 DFD圖 （√ ）。 2．數(shù)據(jù)庫中只有一個模式，也只有一個內模式，所以模式／內模式映像是惟一的。（√ ）。 3． SQL Server 數(shù)據(jù)庫中的 NULL 值（空值）表示的是 “空格”或“ 0”值（ ） 4． SQL Server 中的 tempdb 數(shù)據(jù)庫是一個臨時數(shù)據(jù)庫，屬用戶數(shù)據(jù)庫（ ） 5． SQL 雖被稱為“查詢語言”，其功能卻丌僅僅限亍查詢（√ ） 1．計算機數(shù)據(jù)處理技術大致經(jīng)歷了人工管理、文件管理和 SQL Server 數(shù)據(jù)庫管理三 大階段（ ╳）。 2． 能夠 惟一 表示數(shù)據(jù)表中的每 條 記錄的字段或者字段的組合 稱為 主碼 或主鍵（ √）。 3． SQL Server 數(shù)據(jù)庫中的 NULL 值（空值）表示的是 “空格”或“ 0”值（ ╳） 4．一個 丌規(guī)范的關系模式通常會引發(fā)揑入異常、刪除異常和更新異常，導致大量的數(shù)據(jù)冗余。（ √） 5．目前的關系數(shù)據(jù)庫系統(tǒng)一般都支持標準 SQL 語句（ √） 1． DELETE TABLE 的功能是刪除表結構。（ ） 2．在教師任課關系（教師編號，教師姓名，教師職稱，課程號，課程名，課時費）中，主鍵是教師編號。（ ） 3． 觸發(fā)器是一種特殊 的存儲過程，它基亍一個表創(chuàng)建，可以針對多個表進行操作。 （√） 4．做結構設計時，要盡量使設計符合第三范式的要求。（√ ） 5．登錄賬號用亍身份驗證，用戶賬號用亍權限驗證。（√ ） Visafree policy brings Chengdu biz, tourism boost. Making national headlines several times, Chengdu39。s 72hour visafree policy has attracted wide attention from both Chinese and foreign experts and businessmen since it took effect on Sept 1 last year. The program permits citizens from 51 countries and regions including the United States, Australia, Canada and Japan who have valid visas and flight tickets to a third country to spend three days in the city. The capital of Sichuan province is the first city in the western region of China to offer foreign tourists a threeday visa and the fourth nationwide to adopt the policy following Shanghai, Beijing and Guangzhou. Li Zhiyong, deputy dean of the tourism institute at Sichuan University, said the move contributes to a large increase in the number of overseas tourists and raises the city39。s level of internationalization. The policy will also bring direct economic revenue, Li said. Chengdu has many cultural legacies and is also a paradise for panda lovers with the world39。s largest breeding and research center. Three days are long enough for foreign visitors to visit those iconic tourist spots, he noted. The city is home to the remains of the Jin sha civilization that dates back more than 3,000 years as well as the Qing cheng Mountains and the Du jiang yan irrigation system. Qing cheng has long been recognized as the birthplace of Taoism, China39。s ancient indigenous religion, while Du jiang yan is considered to be the oldest functioning watercontrol project in the world. Chengdu ranked third in tourist facilities, management and services among 60 Chinese cities in a customer satisfaction survey released last year. But, Li added that efforts are still needed to develop more tourism products, improve English services and provide accurate translation of traffic signs and scenic billboards. Zhao Yun, chairwoman of British Chamber of Commerce Southwest China, told China Daily that his colleagues found the policy very convenient. A British client once flew here and stayed for just one day to check her ordered goods, she said. Zhao was born in Shanxi province, but she has lived in Chengdu for more than 10 years. My life was like a running race moving from place to place. I also lived in Beijing and Shanghai before, she said. But Chengdu is a place that you never want to leave once settling down. It is now my second hometown, she said. If the environment is further improved, the city will attract more people to visit and live, with the 72hour visafree policy and pelling conditions in transportation, culture, climate and cuisine, he said. Foreigners also gave positive feedback on the policy. A spokesman from Dell Inc said the pany has a global hub of operation in Chengdu, so the threeday visa has an immediate and positive influence on the pany39。s business development. Rudy Buttignol, president of the public broadcasting pany in British Columbia, Canada, said his work requires frequent travel to Chengdu and the policy makes the trips easier. Data from the city39。s public security bureau shows some 100 foreign visitors enjoyed the 72hour policy by the end of March, most of them from the United States, the United Kingdom and Germany. Chengdu also reported robust growth in its overall tourist industry last year. Official statistics show that it received some 150 million tourists last year, an increase of 28 percent from 2021. Around million came from abroad, an increase of 12 percent. Total revenue from touris m surpassed 133 billion yuan ($). During his visit to Kazakhstan in September, Chinese President Xi Jinping proposed that China and Central Asia join hands to build a Silk Road economic belt to boost cooperation. The idea has been widely echoed in Central Asian countries, being an encouraging blueprint for Chinese areas along the Silk Road that has linked Asia and Europe for more than 2,000 years. In the next three weeks, China Daily reporters will travel through the belt in China and in Kazakhstan, Uzbekistan and Turkey. They will show the progress and expectations of the countries, busine