Developing multi-tier database applications with BCB

After the client/server structure in MRP, MIS and other database application system, multi-layer structure (Multi_tier) began to debut, many vendors provide a variety of middleware. This article describes a method for developing multi-tier database applications using the Multi_tier artifacts provided by the Borland C + + Builder (hereinafter referred to as BCB).

The realization of multi_tier structure

The Multi_tier proposed by C + + Builder is to take BDE, SQL link and datamodule from previous Client/server front-end applications to another NT Server, also known as an application server, The front-end machine leaves only the application and DBClient.DLL, and the datamodule that moves to the application server becomes a COM program that transmits SQL to the back-end database via BDE, SQL link, and accesses data from the back-end database. The Tdatasetprovider component then compresses the read dataset and cuts it into a segment of the packet (data packet) through the DCOM mechanism to the front-end machine, The DBClient.DLL on the front-end machine restores the received packets to the TClientDataSet components in the program, and the data Control component can be tclientdataset for the source. The COM program correctly writes the modified dataset back to the back-end database.

Compared with the client/server structure, the multi_tier structure has many advantages, which are mainly shown in:

1. Significantly reduce the burden on the database server. Because more than one layer of application servers, taking over the connection processing of many clients, the database server only needs to deal with the connection of the application server, which will not affect the performance of the system because of the increase of user (client) number.

2. Front-End machine application installation is convenient. In the multi_tier structure, the BDE, SQL link, and Datamodule in the previous Client/server front-end application are taken to a small number of application servers, and the front-end machine is responsible only for use interface processing, Only need a simple EXE file (including DBClient.DLL), you can develop front-end applications on the application server, replicated over the network to the various front-end machines.

Second, the Environment configuration

1. Back-End Database server configuration

It includes database system and middleware provided by database. The specific environment of this article is:

Install Oracle7.3 on VMS operating systems.

2. Application Server Configuration

(1) Install Windows NT on PC server to make it a Microsoft NT server;

(2) To ensure the smooth network, that is, the network layer of communication protocols unblocked;

(3) Install the middleware provided by the database system, this article is oracle for NT sqlnet products, execute sqlnet Easy Configuration tool, set Oracle's TNS connection parameters, add a database alias, The Oracle database server connected to the back end;

(4) Install BDE Administrator, set the BDE parameter content, the concrete steps are as follows:

Databases to create a new alias first, this article is Oracle2, where the arguments are as follows:

Alias of the server name database server

NET protocol TNS

User name Oracle username/password

(5) installs the C++builder 5 software, uses in the development application server and the client's program.

3. Front-End Client Configuration

(1) Install the operating system Windows 95/98, this is Windows 98, to ensure that each front-end machine and application server in the TCP/IP layer connectivity;

(2) Copy DBClient.DLL from the \Winnt\System32 directory of NT Server to the \Windows\System of this machine;

(3) If the operating system is Windows 95, the DCOM program must be installed because Windows 98 and Windows NT Workstation already contain DCOM programs and do not require additional installation;

(4) Develop applications on the application server and replicate over the network.