數(shù)據(jù)庫(kù)管理-外文翻譯-數(shù)據(jù)庫(kù)-展示頁(yè)
2025-01-31 11:57本頁(yè)面
【正文】 allow retrieval of the information. Early system were arranged sequentially (., alphabetically, numerically, or chronologically)。 the development of directaccess 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 puter 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. The many users of a large database must be able to manipulate the information within it quickly at any given time. Moreover, large business and other anizations tend to build up many independent files containing related and even overlapping data, and their data, processing activities often require the linking of data from several files. Several different types of database management systems have been developed to support these requirements: flat, hierarchical, work, relational, and objectoriented. In flat databases, records are anized according to a simple list of entities。 the speed and versatility of work databases have led to their wide use in business. Relational databases are used where associations among files or records cannot be expressed by links。 this database structure is the most flexible and adaptable. The information in many databases consists of naturallanguage texts of documents。數(shù)據(jù)庫(kù)與其它數(shù)據(jù)處理操作協(xié)同工作，其結(jié)構(gòu)要有助于數(shù)據(jù)的存儲(chǔ)、檢索、修改和刪除。 一個(gè)數(shù)據(jù)庫(kù)由一個(gè)文件或文件集合組成。域是數(shù)據(jù)庫(kù)存儲(chǔ)的基本單位，每個(gè)域一般含有由數(shù)據(jù)庫(kù)描述的屬于實(shí)體的一個(gè)方面或一個(gè)特性的信息。 數(shù)據(jù)庫(kù)的記錄和文件必須被組織起來(lái)，以確保能對(duì)信息進(jìn)行檢索。用戶檢索數(shù)據(jù)庫(kù)信息的主要方法是 query（查詢）。比如，用戶必須能在任意給定的時(shí)間內(nèi)，能夠快速處理內(nèi)部數(shù)據(jù)。為滿足這些要求，開(kāi)發(fā)出各種不同類型的數(shù)據(jù)庫(kù)管理系統(tǒng)，如：非結(jié)構(gòu)化的數(shù)據(jù)庫(kù)、層次型數(shù)據(jù)庫(kù)、網(wǎng)絡(luò)型數(shù)據(jù)庫(kù)、關(guān)系型數(shù)據(jù)庫(kù)、面向?qū)ο笮蛿?shù)據(jù)庫(kù)。層次型數(shù)據(jù)庫(kù)按樹(shù)型組織記錄，每一層的記錄分解成更小的屬性集。與此不同，網(wǎng)絡(luò)型數(shù)據(jù)庫(kù)在不同記錄集之間提供多個(gè)鏈接，這是通過(guò)設(shè)置指向其它記錄集的鏈或指針來(lái)實(shí)現(xiàn)的。當(dāng)文件或記錄間的關(guān)系不能用鏈表達(dá)時(shí)，使用關(guān)系型數(shù)據(jù)庫(kù)。多個(gè)關(guān)系可通過(guò)數(shù)學(xué)關(guān)系提供所需信息。 很多數(shù)據(jù)庫(kù)包含自然語(yǔ)言文本信息，可由個(gè)人在家中使用。典型的商業(yè)應(yīng)用包括航班預(yù)訂、產(chǎn)品管理、醫(yī)院的醫(yī)療記錄以及保險(xiǎn)公司的合法記錄。這些數(shù)據(jù)庫(kù)存有諸如摘要、報(bào)表、成文的法規(guī)、通訊錄、報(bào)紙、雜志、百科全書(shū)、各式目錄等資料。目前有上萬(wàn)種可公開(kāi)訪問(wèn)的數(shù)據(jù)庫(kù)，內(nèi)容包羅萬(wàn)象，從法律、醫(yī)學(xué)、工程到新聞、時(shí)事、游戲、分類廣告、指南等。 DBMS Structuring Techniques Sequential, direct, and other file processing approaches are used to anize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquiries for informatio
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