A new approach to tackling enterprise application integration (EAI) could bring about a major shift in the EAI software and application server markets.

Enterprise service bus (ESB) software, which uses messaging to transport data between connected applications, is rapidly gaining acceptance among enterprises because it provides a low-cost way of overcoming many interoperability problems.

An ESB avoids a spaghetti of company application interconnections because existing applications, services and other data sources need only to plug into the bus to communicate.

Analyst Gartner has predicted that most companies will run an ESB by 2005.

This approach is seen by analysts as a potential threat to EAI companies through its low cost and flexibility. It is also a threat to application server vendors, partly because an application server's hub-and-spoke architecture is a bottleneck for high data volumes and a single point of failure.

"Butler Group supports bus rather than the hub-and-spoke architecture for the majority of companies," said Mike Thompson, principal research analyst at Butler Group. "This will help redefine the application server market to a large extent."

He said the arrival of web services had encouraged companies to look at their strategies afresh.

"It doesn't weaken the case for web services but with an ESB it really is irrelevant what type of connection is used. Flexibility is the key," Thompson said.

Enterprises will not remove large systems. But Butler Group and other analysts see ESB being increasingly adopted for new developments precisely because it can be installed without disrupting existing applications and ways of working.

It needs to be standards-based for interoperability and future proofing, and the only choice to emerge for messaging so far is the J2EE messaging standard (JMS).

To this an ESB adds facilities such as routing and data transformation plus a set of standards-based connectors such as web services and Java Connector Architecture (JCA), along with other connectors for specific applications.

One company benefiting from the shift to ESB is Progress Software's message-oriented middleware (MOM) subsidiary, Sonic Software.

Sonic Software's JMS-based SonicMQ MOM has built its market share to over 500 global enterprise users, which it puts down to high performance and standards-compliance.

"It's an asynchronous world," said Tim Dempsey, Sonic's vice president of marketing. "Global enterprises will deploy ESBs. It's the foundation for the real-time enterprise because it provides a highly distributed, service-oriented architecture that is standards-based - which is what they are looking for."

Sonic introduced its SonicXQ ESB in rudimentary form late last year and has since been building functionality.

Progress's purchase of eXcelon, announced last month, will add an XML document database and business process management for itinerary-based routing of data.

Dempsey said an ESB eased integration of best-of-breed applications and also opened up secure communication with trading partners across the firewall.