tailieunhanh - Databases Demystified a self teaching guide phần 8

Chúng tôi sẽ tập trung vào công việc thiết kế vật lý của thiết kế cơ sở dữ liệu, mà là chuyển đổi thiết kế cơ sở dữ liệu hợp lý vào một hoặc nhiều thiết kế cơ sở dữ liệu vật lý. Trong những tình huống nơi mà một hệ thống ứng dụng đang được phát triển để sử dụng nội bộ, nó là bình thường để có một thiết kế cơ sở dữ liệu vật lý cho mỗi thiết kế hợp lý. | CHAPTER 9 Connecting Databases to the Outside World Invoking Transactions from Web Pages There are several ways in which information in a web request received by the web server can invoke a transaction on the application server. These methods are detailed in the following subsections. CGI Common Gateway Interface CGI Common Gateway Interface is a specification for transferring information between a web server and a CGI program. The CGI script sometimes called a CGI program runs on either the web server or application server. CGI defines how scripts communicate with web servers. The URL points to the CGI script and the server launches it. The actual script can be written in a variety of languages such as Perl and Visual Basic. In essence instead of the URL in the incoming request pointing directly to an HTML document it points to a script. This script is run and the output from the script is an HTML document that is then returned to the client in response to the request. The advantages of CGI include the following Simplicity Language and web server independence Wide acceptance Here are the disadvantages The web server is always between the client and the database. No transaction support stateless . Not intended for long exchanges. Each CGI execution spawns a new process or thread which presents resource issues. CGI is not inherently secure. Server-Side Includes Server-Side Includes SSI has commands embedded in the document that cause the web server to execute a program as with CGI and incorporate the output into the document. Essentially SSI is in an HTML macro. The URL in the request points to an HTML document but the web server parses the document and handles any SSI commands before returning the document to the requesting client. SSI solves some of the CGI performance issues but it offers few other advantages or disadvantages. Databases Demystified Non-CGI Gateways Non-CGI gateways work like CGI gateways except that each is a proprietary extension to a specific .