Introduction

Creating network applications that can communicate directly over the network is the subject of this chapter. The advanced techniques described here cover ways in which two or more applications can create a channel over the network and exchange information. This is ideal for applications such as groupware and scheduling systems where clients need to check with other clients on the status of an appointment. These functions, generally called interprocess communications, form the basis of any client-server application.

In this chapter, I also cover Network DDE. Much like standard DDE, this system allows one application to launch an application on another client via the network and has been used in one memorable example to demonstrate distributed computing power of networked PCs to rival a supercomputer! However, for more day-to-day applications it is an excellent and easy-to-use method of sharing information over the network.

Network DDE

Network DDE provides a Dynamic Data Exchange data link over a network. Standard DDE takes place between two different applications on a single machine; for example, calling Microsoft Excel from within Visual Basic. Network DDE enables applications on different machines to communicate; the other main difference is that Network DDE also allows the same application running on different PCs to communicate. This makes the system ideal as a data channel for groupware, scheduling, version control or other systems where each user needs the same application delivered to his desktop. To give you an idea of how Network DDE operates, Windows provides a few simple...