【正文】 s task is the request concerning accepting user , need to be first conducted and corresponding to expand application program and database to carry out connection , passes through the waies such as SQL to database server to put forward data handling to apply for, then etc. database server the result of handling data submit to Web server, deliver again by Web server to return customer end. The number of plies of 3th according to layer: Database server. In data layer contain systematic data handling logic, locate in database server end. It39。今后，軟件升級和維護會越來越容易，而使用起來會越來越簡單，這對用戶人力、物力、時間、費用的節(jié)省是顯而易見的，驚人的。運行數(shù)據(jù)庫服務(wù)器程序的機器，也稱為應(yīng)用服務(wù)器。它是隨著 Inter技術(shù)的興起，對 C/S結(jié)構(gòu)的一種變化或者改進的結(jié)構(gòu)。 保障系統(tǒng)的安全性：在 Client/Server 系統(tǒng)中由于客戶機直接與數(shù)據(jù)庫服務(wù) 器進行連接，用戶可以很輕易的改變服務(wù)器上的數(shù)據(jù)，無法保證系統(tǒng)的安全性。 仔細分析不難看出，三層的 Browser/Server 體系結(jié)構(gòu)是把 二層 Client/Server 結(jié)構(gòu)的事務(wù)處理邏輯模塊從客戶機的任務(wù)中分離出來，由單獨組成的一層來負擔其任務(wù)，這樣客戶機的壓力大大減輕了，把負荷均衡地分配給了 Web 服務(wù)器，于是由原來的兩層的 Client/server 結(jié)構(gòu)轉(zhuǎn)變成三層的 Browser/Server 結(jié)構(gòu)。如下圖所示： 這種結(jié)構(gòu)解決了傳統(tǒng) Client/Server 的可擴展問題，既減少了客戶端業(yè)務(wù)邏輯，又降低了客戶端對硬件的要求。從技術(shù)上看，它本身是一個邏輯概 念，是指將一個應(yīng)用分解成多個任務(wù)分別執(zhí)行，共同完成整個應(yīng)用任務(wù)的功能。網(wǎng)絡(luò)各站點主機上資源（硬件、軟件、數(shù)據(jù)）分步不均衡，在客戶 /服務(wù)器結(jié)構(gòu)下，無資源的客戶機通過向有資源的服務(wù)器發(fā)出請求，并得到資源請求，從而適應(yīng)網(wǎng)絡(luò)中資源分布的不均衡性。同時，由于把許多業(yè)務(wù)邏輯集中到了單一的應(yīng)用服務(wù)器上，應(yīng)用系統(tǒng)的維護工作也被集中到了一起，消除了傳統(tǒng) Client/Server 結(jié)構(gòu)中軟件分發(fā)的問題。這種三層體系結(jié)構(gòu)如下圖所示。Browser/Server 系統(tǒng)在客戶機與數(shù)據(jù)庫服務(wù)器之間增加了一層 Web 服務(wù)器，使兩者不再直接相連，客戶機無法直接對數(shù)據(jù)庫操縱，有效地防止用戶的非法入侵。在這種結(jié)構(gòu)下，用戶工作界面是通過 WWW瀏覽器來實現(xiàn)，極少部分事務(wù)邏輯在前端 (Browser)實現(xiàn)，但是主要事務(wù)邏輯在服務(wù)器端 (Server)實現(xiàn)，形成所謂三層 3tier 結(jié)構(gòu)。一旦服務(wù)器程序被啟動，就隨時等待響應(yīng)客戶程序發(fā)來的請求；客戶應(yīng)用程序運行在用戶自己的電腦上，對應(yīng)于數(shù)據(jù)庫服務(wù)器，可稱為客戶電腦，當需要對數(shù)據(jù)庫中的數(shù)據(jù)進行任何操作時，客戶程序就自動地尋找服務(wù)器程序，并向其發(fā)出請求，服務(wù)器程序根據(jù)預(yù)定的規(guī)則作出應(yīng)答，送回結(jié)果，應(yīng) 用服務(wù)器運行數(shù)據(jù)負荷較輕。因此，維護和升級革命的方式是“瘦”客戶機，“胖”服務(wù)器。s task is to accept the request that Web server controls for database, realization is inquired and modified for database , update etc. function, submit operation result to Web server. Careful analysis is been easy to see , the architecture of Browser/Server of threelayer is the handling of general affairs of the two levels of structure of Client/Server logic modular from the task of client puter in split , from the first floor of individual position bear the pressure of its task and such client puter have alleviated greatly, distribute load balancedly and have given Web server, so from the structural change of Client/server of original two floor the structure of Browser/Server of threelayer. This kind of threelayer architecture following picture shows. This kind of structure not only client puter from heavy burden and the requirement of performance that rises continuously for it in liberation e out , also defend technology people from heavy maintenance upgrading work in free oneself. Since client puter handles general affairs , logic partial minutes have given function server, make client puter right off slender a lot of, do not take the responsibility for handling plex calculation and data again visit etc. crucial general affairs, is responsible to show part, so, maintenance people do not rush about again for the maintenance work of program between every client puter, and put major energy in the program on function server update work. Between this kind of threelayer structural layer and layer, the mutually independent change of any first floor does not affect the function of other layer. It has changed the defect of the two levels of architecture of Client/Server of tradition from foundation, it is the transform with deep once in application systematic architecture. The contrast of two architectures The architecture of Browser/Server and the architecture of Client/Server pare with all advantages that not only have the architecture of Client/Server and also have the architecture of Cli/Server the unique advantage that place does not have: Open standard: The standard adopted by Client/Server only in department unification for but, it39。s task is to suggest by Web browser to the certain a Web server on work that service is asked , after verifying for user identity, Web server delivers needed homepage with HTTP agreement to customer end, client puter accept the homepage file that passed , and show it in Web browser on. Second layer function layer: Have the Web server of the application function of program extension. In function layer contain the systematic handling of general affairs logic, locate in Web server end. It39。所以客戶機越來越“瘦”，而服務(wù)器越來越“胖”是將來信息化發(fā)展的主流方向。二者可分別稱為前臺程序與后臺程序。 B/S(Browser/Server)結(jié)構(gòu)即瀏覽器和服務(wù)器結(jié)構(gòu)。 Browser/Server 系統(tǒng)的三部分模塊各自相對獨立，其中一部分模塊改變時其它模塊不受影響，系統(tǒng)改進變得非常容易，且可以用不同廠家的產(chǎn)品來組成性能更佳的系統(tǒng)。它的任務(wù)是接受Web 服務(wù)器對數(shù)據(jù)庫操縱的請求，實現(xiàn)對數(shù)據(jù)庫查詢、修改、更新等功能，把運行結(jié)果提交給 Web 服務(wù)器。因此其結(jié)構(gòu)就變成了新的 (Client 應(yīng)用+Server 應(yīng)用 )/Server 結(jié)構(gòu)。 客戶 /服務(wù)器（ Client/Server）模型是一種良好的軟件體系結(jié)構(gòu)，是網(wǎng)絡(luò)的最佳應(yīng)用模式之一。采用這種結(jié)構(gòu)能綜合各種計算機協(xié)同工作，各盡其能，實現(xiàn)對計算機系統(tǒng)的規(guī)模優(yōu)化（ Rightsizing）和規(guī)模縮小化 (Downsizing)。這種結(jié)構(gòu)即被稱為 B/S 體系結(jié)構(gòu)。 這種結(jié)構(gòu)不僅把客戶機從沉重的負擔和不斷對其提高的性能的要求中解放出來，也把技術(shù)維護人員從繁重的維護升級工作中解脫出來。 三層的 Browser/Server 體系結(jié)構(gòu)具有許多傳統(tǒng) Client/Server 體系結(jié)構(gòu)不具備的優(yōu)點，而且又緊密的結(jié)合了 Inter/Intra 技術(shù)，是技術(shù)發(fā)展的大勢所趨，它把應(yīng)用系統(tǒng)帶入了一個嶄新的發(fā)展時代。這樣就大大簡化了客戶端電腦載荷，減輕了系統(tǒng)維護與升級的成本和工作量，降低了用戶的總體成本 (TCO)。 (2)數(shù)據(jù)的儲存管理功能較為透明。 (2)成本降低，選擇更多。s application is often for special purpose. It is lower to develop and defend cost: It need to be implemented on all client puters that the application of Client/Server must develop the customer end software for special purpose, no matter installation and disposition escalate still, have wasted manpower and material resources maximumly. The application of Browser/Server need in customer end have general browser , defend and escalate to work in server end go on , need not carry out any change as customer holds , have reduced the cost of development and maintenance so greatly. It is simple to use , interface friendly: The interface of the user of Client/Server is decided by customer end software, interface and the method of its use are not identical each, per popularize a system of Client/Server ask user study from the beginning, is hard to use. The interface of the user of