Then the safety factor played a role. For the end user to run applications on a computer (Web-based or "rich client"), any system administrator or Anquanguwen Du Bu Keneng recommended to Bao Han's 鏁版嵁搴?mission-critical data directly Fangzai behind a firewall (for example, from the safe operation of the computer outside the scope of direct access). If adding an intermediate computer and then put another firewall, you can create a separate zone or DMZ often referred to as the region in which to further restrict access to the database. A DMZ greatly strengthen the security infrastructure, reducing the likelihood of a successful infiltration. This not only prevents data from being stolen, but also help protect the server (and the rest of the application or system) from a successful denial of service attacks.
Owners of many large systems favor n (physical) layer system, another factor is the deployment, which will be physically placed in the client software can access the computer process. In the traditional client / server environment, business logic and presentation logic and data access logic are intertwined, so that programmers feel very uncomfortable: the need for new updates each time (for example, need to change the way business data processing or to increase The new view of data), located in the user desktop "fat client" must be replaced and / or adding new code. This means that, at least at this time, someone (usually the developer or system administrator, whichever is the lower level of a) the need to run in all computers, to install the new code. Or require users to download the latest code from the network. Of course, most users are not neglected this point is not correct operation. These two cases do not make frequent release of such wise people really trust. And deployment will take time, and during this time, the system must suspend work, in order to avoid the Yingyongchengxu caused by a mix version of the database caused rush Caozuo any type of Yuyishuoju damage.
The deployment of factors influence the people n (physical) layer model, especially for Web-based applications preferred level. Now people do not need the code then deployed to the user desktop, and can be deployed to the (single) Web server, the end user's browser to select only those changes, but it does not need any further work. For its part, does not roll out the deployment of n (physical) layer system, the reasons; in the traditional client / server application environment of the times can not be obtained by adding a number of options is now possible to deploy the program list, which includes " No-touch deployment "(in. NET 1.x middle) and ClickOnce (in. NET 2.0 in), not to mention people of various mixed AJAX and growing interest in the structure. In fact, the release will update itself when you start rich client application (such as software manager at iTunes, Windows Media Player, or even popular. NET Reflector of development tools, see) has become increasingly more generally.
N a physical layer with the third reason would be that people are often mentioned, Danwangwangque Bu Neng really achieve, Ji Cheng Wei intermediate physical layer logic of some 涓氬姟 a focal point Zhexie logic can be more than the performance of physical layer Fang Wen You, but They can not know. On this point is the classic example of combined intranet / extranet application environment, including internal employees to use WinForms (soon to upgrade to Windows Presentation Foundation) applications to access the middle tier system, the middle layer of the system can then access the database, while the external users (partners and / or customers) to use ASP.NET or may be based on SharePoint's Web site to carry out the same operation: access to the middle layer, middle layer can then access the database.
Although this idea seems very simple in concept, but the structure proved to come from reliable it is extremely difficult to achieve. Because of this reason, the distinction between physical and logical and increasingly more important. If the performance (logical) layer, business logic (logic) layer and the middle of (physical) layer of a clear distinction between, it may be business logic embedded in the client (physical) layer (if it is a rich client application front end) and by avoiding network access to significant savings in performance.
However, the design in two different (physical) layer used in the business logic is very difficult to do. This means that business logic (logic) level must be avoided for performance (logical) layer or data access (logical) layer is common in the same (physical) layer to make any assumptions, this way we must assume that neither in one. Specifically, for the practice run in the middle of (physical) layer of the remote business object server implementation of data binding (via. NET Remoting), this can ruin an application. Now, every property access and method calls are traversing a network, performance will be compared with ... ah ... so bad than the constructed structure of the system designer's reputation has fallen even faster.
Fortunately, the structure of designers around the world has begun to realize that "distributed objects" approach, risks, and now the main theme of the times is the "loose coupling" and "coarse-grained communication", all of which need to be service-oriented method support the structural system. And other aspects of software development, service-oriented has its own flaws, but that is another column topic in other months.
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