These products didn't provide facilities to support the generation of a user interface or what we refer to as "Presentation Services."

Web Application Servers
Starting around 1994, the major drive to create dynamic interactive Web applications spawned a new kind of middle-tier product: the Web application server. The first generation of this kind of product was simply a Web server running CGI scripts. The second generation focused on making it easier to develop and deploy dynamically generated HTML pages, taking over where CGI scripts left off. In this generation the primary purpose of these products was to provide presentation services (see Figure 1). A major limitation of this architecture was that business logic was being embedded in scripts inside Web pages.

The Next Step
As Web application servers evolved, they added important facilities to increase their usefulness (see Figure 2).

It's worth noting that EJB is a long-term vision. In version 1.0 the specification is immature and leaves many key areas undefined. Most players expect that the standard won't reach the level of maturity that will make it widely usable until version 2.0.

Web Application Servers Meet Distributed Objects
So far we've described two separate markets, the first consisting of object, transaction and connectivity services with no presentation services; the second, a market driven primarily by the need to deliver thin-client presentation support.

In mid-1998 these two worlds collided, resulting in major market confusion (see Figure 3). Leading up to the collision was increasing industry recognition that middle-tier distributed objects provided the right architecture for the creation of larger-scale sophisticated applications. Sun's Enterprise JavaBeans (EJB) specification was the catalyst for the collision. It provided a standard specification for how these middle-tier objects should be written, and made them far easier for the developer to write (the hard work would be done by the EJB container and server vendors).

A Market Thrown into Confusion
Both the application server vendors and the vendors of object and transaction services realized that they needed to support the EJB standard; at this time a variety of different products changed their name to application server. All of a sudden there were 40 application server vendors, each offering widely different types of functionality. Some were focused on Web applications, offering strong presentation services; many others were pure object servers with no presentation services at all.

What Does It Take to Be an Application Server?
As a result of the two markets converging, it is clear that we need a new definition of what is required to be an application server. Are presentation services important? Are connectivity services a requirement? Should the server come with integrated development tools?

The following section outlines where I believe the market is headed and explains the different component parts.

Where the Market Is Headed
I believe that customers are looking for an application server that combines all the services shown in Figure 4.

The rationale for each of the components follows:

Where the Players Are Today
Figure 5 shows three different types of players. Examples of pure presentation servers are Allaire's ColdFusion and Microsoft's Active Server Pages (ASP). Examples of pure object servers are products like Iona, Oracle and WebLogic. Few products combine both presentation and object services in an integrated package. SilverStream and NetDynamics are examples.

It should be pointed out that no vendor has all the attributes required today, particularly as it will most likely require version 2.0 of the EJB spec to achieve this, and that is not yet available. Clearly, the right-hand group shown in Figure 5 is nearest to where the market is headed.

The Importance of Neutrality
Application servers are expected to integrate with the wide variety of existing architectures and standards that exist in today's typical customer environment. These include:

Based on the foregoing, customers are looking for application server vendors that are neutral and don't have a particular bias toward an operating system, data source, etc. Several of the application server vendors don't meet this requirement and consequently don't provide the necessary level of support for other competing products. This is generally considered a major drawback.

Summary
This market has undergone substantial change in the last 12 months. It is still maturing and will probably take another 12 to 18 months to sort itself out. Most companies will be evaluating and deciding on their standards during 1999 and 2000 as this is a time-critical technology that must be used now to remain competitive. Although a single winner has not yet emerged, the leaders are clearly separating from the pack based on vision, technology, ability to execute, support services and strength of installed base. A clear requirement is that the product must integrate all of the above services, in particular offering strong presentation services combined with strong distributed object and transaction services.