tailieunhanh - Sams Teach Yourself Database Programming with Visual C++ 6 in 21 Days phần 5

chẳng hạn như Internet Information Server (IIS) và / hoặc Yêu cầu một đối tượng môi giới (Box) chẳng hạn như giao dịch Microsoft Server (MTS). Tầng máy chủ thường bao gồm một máy chủ đang chạy một cơ sở dữ liệu quan hệ. Khách hàng chương trình lớp thường giao tiếp với các chương trình trên lớp giữa, sau đó | Teach Yourself Database Programming with Visual C 6 in 21 days -- Day 11-Multitier Architectures running on different computers T SimpcePDRM ergs andSplit UnregisterediVersion -http CR LF data compression and data encryption J The application layer which provides high-level functions such as device redirection remote file access remote printer access and interprocess communication NOTE The designers of the OSI model carefully crafted the interfaces between the OSI layers so that the layers would be independent. The interfaces were created in such a way as to enable the implementation of one layer to be changed without the need to change the implementation of its neighboring layers. The OSI model has proven to be very successful. Disparate computer systems can now readily communicate with each other using this layered approach. TCP IP is a protocol that adheres to the OSI model. Figure illustrates how the layers of TCP IP map to the layers of the OSI model. Figure How TCP IP layers correspond to the OSI model. TCP IP is the protocol of the Internet. As you will see later the nature of TCP IP and the nature of the OSI model figure prominently in the way multitier applications are developed. Layered Architecture for Multitier Applications When you build multitier applications you can apply important lessons from the OSI model to make your applications successful. NOTE When you build multitier applications you must carefully craft the interfaces between the tiers so that the tiers are independent. You need to create the interfaces in such a way that the implementation of one tier can be changed without the need to change the implementation of its neighboring tiers. Interfaces and abstractions are the two pillars on which multitier applications rest. Each tier that provides an effective level of abstraction has interfaces that are understandable and distinct. Distinct interfaces between the tiers enable the tiers to be updated independently