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Tip of the Day
Language: Enterprise JavaBeans
Expertise: Beginner
Jan 18, 2000

EJB Scalability

Question:
One of EJB's obvious design goals was to provide an environment that can scale up to meet the demands of enterprise applications. I'm curious, however, about the other end of the scalability spectrum as well. I would like to write an application that can scale up to meet enterprise demands, but can also be easily used by a single individual working on a non-networked laptop computer. If I build my application with EJB, will I alienate this user base?

Answer:
You will not necessarily alienate non-networked individuals by using EJB, but you will have to package the EJB components and runtime environment for the individual. Therefore, EJBs that mediate access to multi-gigabyte databases are a no-go. A quick analogy is the use of CORBA on the desktop in the same role of COM as is done by the GNOME desktop environment for Linux. Distributed objects just give you a simpler way of performing interprocess communication and it's ok for that communication to happen on the same machine.

However, your caution is well-justified. EJB is designed for relatively coarse-grained components involved in transaction-oriented distributed applications. This involves modeling database entities and business rules as objects. The typical EJB deployment environment is in three-tier systems. The first tier usually contains a relatively thin client. The second tier contains EJB components that validate inputs, enforce business rules, and mediate access to databases. The third tier contains the actual databases that drive the application. But three-tier systems need not be deployed across a network. They can be deployed on a laptop. By doing so, you gain the advantage of not having to rearchitect your network application for the desktop.

An important thing you lose by using EJB is the ability to produce a lightweight application for the low-end. The key is to use the approach where appropriate. It is easy to imagine a sales database query system implemented with EJB. Salespeople may need to replicate a subset of the enterprise data to their laptops for use when they go out in the field. There would be no reason to redesign the distributed application when it could run unchanged in the single user environment. However, it would probably impose a larger footprint than a reimplemented system because of the need to bundle the EJB server.

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