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An interactive clusteringbased approach to integrating source query interfaces on the deep Web.In: Weikum G, K246。199。188。190。? 嵌入式DBMS 包括Oracle 9i Lite,Informix Cloudscape,人大“小精靈” [38] ,分別占用1MB~2MB 的內(nèi)存空間,適用于掌上電腦等設(shè)備.各種微小型數(shù)據(jù)庫(kù)系統(tǒng)分類及主要特點(diǎn)見(jiàn)表2 [36] .微小型數(shù)據(jù)庫(kù)系統(tǒng)與操作系統(tǒng)和具體應(yīng)用集成在一起,嵌入在移動(dòng)設(shè)備上的數(shù)據(jù)庫(kù)系統(tǒng)涉及數(shù)據(jù)庫(kù)技術(shù)、分布式計(jì)算技術(shù),以及移動(dòng)通信技術(shù)等多個(gè)學(xué)科領(lǐng)域.隨著電子銀行、電子政府以及移動(dòng)商務(wù)應(yīng)用的增加,開(kāi)始涉及一些復(fù)雜的查詢?nèi)邕B接和聚集,并且為了保證數(shù)據(jù)的一致性,提出了原子性和持久性的要求,同時(shí)對(duì)移動(dòng)設(shè)備上數(shù)據(jù)訪問(wèn)的安全性也提出了較高的要求,為滿足日益增長(zhǎng)的數(shù)據(jù)處理需求及方便應(yīng)用的開(kāi)發(fā),對(duì)移動(dòng)設(shè)備上的微小型數(shù)據(jù)庫(kù)管理系統(tǒng)的需求也越來(lái)越大. Tabl e 2 Comparison of kinds of tiny databases system表2 各種微小型數(shù)據(jù)庫(kù)系統(tǒng)分類及主要特點(diǎn)傳統(tǒng)的數(shù)據(jù)庫(kù)系統(tǒng)其結(jié)構(gòu)和算法都是基于磁盤(pán)的,它需要大量的RAM 和磁盤(pán)存儲(chǔ)空間,并且使用了緩沖及異步I/O ,移動(dòng)設(shè)備大多只有很小的存儲(chǔ)空間、較低的處理速度以及很低的網(wǎng)絡(luò)帶寬,因此需要對(duì)傳統(tǒng)數(shù)據(jù)庫(kù)進(jìn)行裁減以適應(yīng)移動(dòng)設(shè)備的需求.移動(dòng)設(shè)備所具有的計(jì)算能力小、存儲(chǔ)資源不多、帶寬有限以及Flash 存儲(chǔ)上寫(xiě)操作速度慢等特性,、RAM 的使用、讀寫(xiě)規(guī)則、存取規(guī)則、,應(yīng)該考慮如下設(shè)計(jì)原則:? 壓縮性原則:數(shù)據(jù)結(jié)構(gòu)和代碼都要精簡(jiǎn).RAM 原則:最小化RAM 的使用.寫(xiě)原則:最小化寫(xiě)操作以減少寫(xiě)代價(jià).讀原則:充分利用快速讀操作.存取原則:利用低粒度和穩(wěn)定內(nèi)存的直接訪問(wèn)能力進(jìn)行讀和寫(xiě).安全原則:保護(hù)數(shù)據(jù)不受意外和惡意破壞,最小化算法的復(fù)雜性以避免安全漏洞.微小型數(shù)據(jù)庫(kù)技術(shù)目前已經(jīng)從研究領(lǐng)域向廣泛的應(yīng)用領(lǐng)域發(fā)展,緊密結(jié)合各種智能設(shè)備的嵌入式移動(dòng)數(shù)據(jù)庫(kù)技術(shù)已經(jīng)得到了學(xué)術(shù)界、工業(yè)界、軍事領(lǐng)域和民用部門(mén)等各方面的重視并不斷實(shí)用化. 數(shù)據(jù)庫(kù)用戶界面一直以來(lái),對(duì)于一個(gè)DBMS 給定的信息類型, 世紀(jì)80 年代時(shí),人們提出了少數(shù)優(yōu)秀的可視化系統(tǒng),尤其是QBE 和Visi Cal 年來(lái)至今仍沒(méi)有更優(yōu)秀的系統(tǒng)出現(xiàn),因此人們迫切需要在這方面有所創(chuàng)新[6] .XML 數(shù)據(jù)的出現(xiàn)使人們提出了新的查詢語(yǔ)言XQuery,普通用戶使用這樣的語(yǔ)言還是有一定難度的.隨著數(shù)據(jù)庫(kù)應(yīng)用及信息檢索系統(tǒng)的廣泛普及,(NLIDB)(而不是人工語(yǔ)言或機(jī)器語(yǔ)言)的方式向數(shù)據(jù)庫(kù)系統(tǒng)發(fā)問(wèn)以獲得所需的信息, 世紀(jì)七八十年代就開(kāi)始了這方面的大量研究工作,并研制了若干數(shù)據(jù)庫(kù)自然語(yǔ)