About this chapter
This chapter gives an overview of distributed application development with PowerBuilder.
Distributed application development, also called multitier development, offers a natural way to separate the user interface components of an application from the business logic that the application requires. By centralizing business logic on a middle-tier server, you can reduce the workload on the client and control access to sensitive information.
In a distributed application, the client and server work together to perform tasks for the business user. The client handles all interactions with the user while the middle-tier server provides background services to the client. Typically, the middle-tier server performs most of the processing and database access. To invoke the services of the server, the client calls a method (or function) associated with a component (or object) that resides on the server.
Partitioned applications
Client-side logic for enterprise applications must be as small and efficient as possible to conserve network bandwidth. To accomplish this goal, applications are partitioned into three parts: presentation, business logic, and database access. The database resides on the bottom tier of the enterprise system to maintain and secure the organization's information assets. The business logic resides in the middle tier or server. The presentation is on the user's desktop, or top tier, or is dynamically downloaded to the user's desktop.
The server is then responsible for executing and securing the vast majority of a corporation's business logic. This makes it a critical component in the network-centric architecture. The client communicates with the server, calling middle-tier components that perform business logic.
Web application architecture
A Web application is a variation of the distributed architecture where the client is hosted in a Web browser. PowerBuilder provides a couple of technologies for building Web applications. The architecture of your application varies depending on which technologies you decide to use.
For more information, see Web Application Development with PowerBuilder
PowerBuilder developers can build clients that invoke the services of COM+ and third-party application servers, and build components (or objects) that execute business logic inside each of these servers.
J2EE servers
J2EE, the Java 2 Platform, Enterprise Edition, is the official Java framework for enterprise application development. A J2EE application is composed of separate components that are installed on different computers in a multitiered system. The following figure shows three tiers in this system: the client tier, middle tier, and Enterprise Information Systems (EIS) tier. The middle tier is sometimes considered to be made up of two separate tiers: the Web tier and the business tier.
Figure: J2EE client, middle, and EIS tiers
Client components, such as application clients and applets, run on computers in the client tier. Web components, such as Java servlets and JavaServer Pages (JSP) components, run on J2EE servers in the Web tier. The EIS tier is made up of servers running relational database management systems, enterprise resource planning applications, mainframe transaction processing, and other legacy information systems.
COM+
A PowerBuilder application can act as a client to a COM server. The server can be built using any COM-compliant application development tool and it can run locally, on a remote computer as an in-process server, or in COM+.
For more information, see Building a COM or COM+ Client
