In the three-layer architecture system, the application representation layer (client) and business logic layer (intermediate layer) and data layers may be located in different networks, so the communication between them will become very difficult. And the transactions between components widely used in the intermediate layer will also become intricate. To this end, Microsoft provides system programs that solve these problems, which include: MS Remote Data Services, MS Transaction Server, COM / DCOM / COM , etc. At the client, the data service component of the intermediate layer is created via RDS. The sharing mechanism generates a role when running RDSServer.DataFactory or custom business objects in the Intermediate Trend Server runtime environment. You can still support thousands of clients only for hundreds instead of thousands of database connections. This is the function of the ODBC resource allocator in Microsoft Transaction Server. The intermediate layer and data layers can be connected via ADO to implement data read and write operations. • Use RDS to have three ways to return the RECORDSET from the server to the client. These three ways are: (1), using the RDS.DataControl method and attributes of the RDSServer.DataFactory object. (2), manually call RDSServer.DataFactory object. (3) Creating a custom ActiveX DLL for performing data access functions. Here, our client uses its own intermediate layer object (DCOM / COM ) to process business logic and access data. First, let's take a look at the basic RDS programming model: parameter. The server is called on the server accesses the specified data source, retrieves information, processes the data, and then returns the result information to the client application in the format that is easy to use.
