When application servers first appeared on the computing horizon, they served as a middle tier in client/server applications. This model wasn't widely adopted because it added yet another layer of complexity to the application. However, the Internet revolution changed all that and vaulted the application server to instant fame. Web applications naturally lent themselves to a multitier model of application development. Today, application servers function as a middle layer between user interfaces (such as a Web browser) and the data storage layer (such as a database). The application server contains the business logic that streamlines requests from the client, processes the data, and responds to user requests. Sybase, the database giant, made its presence felt in the Internet software market with its application server offering — EAServer. In its current version, 4.0, it is a highly evolved tool that compares well with the best in the market.

A Complete Package

Like many other application servers, EAServer ships with its own set of development tools. The EAServer product set consists of PowerDynamo (a tool for building Web sites), Adaptive Server Anywhere (a relational database), Application Integrator for IBM's CICS (which integrates legacy CICS applications with EAServer), and Application Integrator for Stored Procedures (which accesses database-stored procedures from EAServer).

EAServer ships in four editions. The Enterprise Edition is ideal for large-scale transaction-processing applications. The Advanced Edition is similar to the Enterprise Edition, except that it doesn't include access to CICS applications, two-phase commit, or fault tolerance. The Small Business Edition is targeted at information-publishing applications. It supports a maximum of 10 active transaction-server connections. Developers can build and test applications using the Developer Edition. It is limited to five Internet Inter-ORB Protocol (IIOP) connections.

EAServer provides a scalable, multithreaded, platform-independent execution engine. The EAServer execution environment is the same across all platforms, except of course the ActiveX component (which only Windows NT supports). I took EAServer for a test drive on a computer running Windows 2000. I found the installation and configuration to be quite straightforward.

Wholehearted Support

Because an application server functions as middleware, its worth depends on the support that it provides to the other elements of the application. For example, it's important to consider whether it supports various component models. Components are reusable modules of code that combine related tasks into a well-defined interface. Most application servers lean toward either the Enterprise Java Bean (EJB) component model or the Microsoft COM/ActiveX component model.

Sybase built its EAServer on a refreshingly open component model right from its early versions. It supports all major component models, including Java Beans, PowerBuilder, Java, ActiveX, and C/C++. Any EAServer client can execute any type of component. A component of any model can execute components of another model using intercomponent calls without the use of additional gateway software. Additionally, since EAServer uses standard CORBA IIOP as its core network protocol, you can use CORBA client run times from other vendors to invoke components installed on EAServer. All clients and components share a common interface repository. Component interfaces are stored in standard CORBA interface definition language (IDL).

Jaguar Manager, included in all editions, lets developers browse, define, and edit interfaces graphically or as raw IDL (see Figure 1). I found the Jaguar's user interface to be very intuitive. You can also define interfaces by importing compiled Java classes, standard-format EJB-JAR files, or ActiveX-type libraries. Jaguar Manager also generates stub classes for use in Java and C++ client applications and ActiveX type libraries for use in ActiveX client applications. You can also use Jaguar Manager to configure EAServer and define and deploy software components and packages. Jaguar Manager enables you to remotely view server log files and monitor statistics for component execution and network activity.

EAServer components can connect to any database for which an ODBC or JDBC driver is available. EAServer can also connect to a Sybase database using the Sybase Open Client Client-Library. It even provides a native connection to its competitor's (Oracle's) database using the Oracle Call Interface (OCI).

In its implementation of the Java 2 Enterprise Edition (J2EE) specification, EAServer supports EJB 2.0 components, J2EE applications, J2EE Web applications, object caching, the JavaMail email API, the connector architecture, Java API for XML Parsing, and the Java Authentication and Authorization Services.

EAServer supports various network protocols. It supports IIOP, the standard protocol for communication between CORBA ORBs over TCP/IP networks. IIOP connections can also be tunneled inside of HTTP to allow connections through firewalls that don't allow passage of IIOP traffic. Tabular Data Stream is a proprietary protocol used in two-tier database applications that connect to Sybase database servers or gateways. EAServer provides HTTP support so you can deploy HTML pages and Java applets on EAServer itself. It also supports the Secure Sockets Layer (SSL) protocol, which enables secure connections using public-key encryption and authentication algorithms. EAServer provides a graphical tool called Security Manager for managing SSL digital certificates.