You're a senior Java engineer who's been working with J2EE on enterprise systems software and applications. You've got a résumé that reads like a who's who and what's what of current technologies.

But when you apply for a job that looks like a perfect fit for your skills, you get a rejection letter. Or even worse, it seems as if your résumé was sucked into a black hole and you never hear anything back at all.

What's going on, you wonder. Why don't these people realize how perfect I am for this position?

Potential employers look at a résumé in a way that's fundamentally different than you might expect. And a lot of it has to do with the type of work ­ and the kind of company ­ that's listed on your résumé.

To understand how people in the industry perceive different types of engineering experience, imagine a box made up of four squares. From the top left, number the squares clockwise, as 1, 2, 3, and 4. These numbers have nothing to do with seniority levels; they're merely a way to visualize four different types of work (see Figure 1).

Boxes 1 and 4 represent the work done at product companies. Boxes 2 and 3 represent the work done at IT organizations. The engineers who work at level 1 build commercial applications that sit on top of the core infrastructures built by engineers at level 4.

When we refer to product companies, we're talking about companies that sell enterprise-wide products to other companies. These include Oracle, Siebel, Arriba, and BEA. Using Oracle as an example, the level 4 engineers are the ones who built the Oracle core platform. The level 1 engineers build applications that run on top of it.

Engineers who build commercial applications must face a special set of problems and challenges. Those who have worked in this environment have experience with building a product that's going to market.

Engineers who work at levels 2 and 3 work for IT organizations, doing similar yet different kinds of work. Examples of IT organizations include the IT divisions of large companies such as Charles Schwab, E*TRADE, or DHL.

The engineers at level 2 build applications, for the company's internal use, that sit on top of the core infrastructure built by engineers at level 3. While these may be powerful, complex systems and applications, there's a fundamental difference between this kind of work and building a product that's going out the door.

In the eyes of those within the industry, it's like looking at two automobile engineers who are both building Fords. One engineer has been building racing cars, the other has been building consumer cars. That's not to say that one type of work is better than the other, but each product demands different skills and experience from the engineer who builds it.

By the same token, an actor who's had a long career in situation comedies is going to have a hard time selling himself to someone who's casting a production of Hamlet. He might be a great Shakespearean actor, but it's going to take some special strategies to sell himself for the role.

Many people fit into more than one of these imaginary boxes, and there's no reason why a skilled engineer couldn't make the transition from one type of work to another. It's a matter of perception on the part of potential employers, and how well you can address those perceptions when applying for the job.

The first step is to realize that based on your résumé, you are being perceived not only by your skills, but by the type of work you've done in the past. The second step is to specifically address potential concerns in a cover letter or within the résumé itself.

Spamming out the same résumé for many different types of positions is the most common mistake made by job-hunting engineers. It takes more time to tailor your résumé and cover letter to each position, but in our experience, it's the only way to catch the serious attention of hiring managers.

An unfortunate fact of life in the hiring world is that most résumés aren't carefully read, they're scanned. Since we're currently in a buyer's market, it's even more critical that you sell yourself carefully and thoughtfully, taking as many issues into account as possible.

By recognizing in which of these four squares a hiring manager might perceive you, you stand a much better chance of positioning yourself to cross over into one of the other squares.

It's ultimately about depth and breadth of experience. Once you've built racing cars, Aerostars, and Escorts, you should be able to get any job building any kind of car you want.

• Figure 1