Frequently asked questions: Enterprise service bus

What is an ESB?

Vendors position ESB as the latest generation of application integration technology, succeeding traditional integration brokers such as messaging middleware. Although specific implementations vary, ESBs share a common set of characteristics.

Stuart Ransom, a vice president at Sonic Software, described the minimum requirements — the ESB table stakes as he put it — as messaging, transformation and routing.

That's consistent with Gartner's ESB definition, which the firm developed in late 2002.

The messaging layer — the B in ESB — provides an intermediary through which applications can communicate. Transformation involves mapping data to a format that both sending and receiving applications can use. Routing helps deposit a message at the proper destination.

How is ESB technology related to SOA?

An ESB supports applications deployed as reusable software components, often referred to as services. Thus, proponents view the technology as a critical element of an SOA, which is a collection of services that an organization can coordinate to support its business processes.

"ESB forms the core platform on top of which an SOA can be deployed," said Atul Saini, chief executive officer, chief technology officer and chairman of Fiorano Software, which develops ESB products.

Web services standards have emerged as a way to achieve interoperability among SOA services. Those standards include Extensible Markup Language for the message format, Simple Object Access Protocol for message transport and Web Services Description Language for interface descriptions.

Ransom said support for Web services is a central ESB requirement. Several ESB vendors employ Web services standards as the means for linking service-based applications. By using Web services, an ESB can deal with applications devised from the beginning as services and with applications accessible via Web services. In addition, ESB vendors often provide optional adapters for older applications that don't support Web services.

Ransom describes ESB as an integration layer "between existing legacy applications and new applications being built."

Although the technology can provide an SOA launching pad, industry observers say vendors could build such an architecture without an ESB.

SOAs "are increasing in popularity, but very few customers have adopted an enterprise service bus," said Michael Beckley, vice president of product strategy at Appian, a provider of business process management products and services.

What are the benefits of using ESB technology?

ESB advocates said customers save time and money by using the technology.

Annrai O'Toole, CEO of ESB vendor Cape Clear Software, said organizations can do without ESB if they don't mind writing a lot of custom code as they deploy SOAs. "It's obviously much quicker and cheaper to look at a productized solution," he said.

O'Toole said SOA pioneers built their buses three or four years ago, adding that fewer people are writing custom software today. He likened the situation to Java's emergence in the mid-1990s. Early adopters built their own Java infrastructure, but application server products eventually became the common infrastructure for building Java applications.

ESB backers also say customers can take advantage of features that go beyond Web services' capabilities. ESB vendors hope to sell customers on their products' scalability, performance and ability to mange a distributed integration environment.

Customers evaluating products "are spending more time on how [vendors] extract performance from the bus and how does it scale," Ransom said.

ESB products may include load balancing/failover, distributed deployment of services and security features that surpass those available in the Web services standards.

How does ESB compare in cost to other integration technologies?

ESBs are considerably less expensive than other integration methods, government and industry executives say.

Mike Gilpin, a vice president and research director at Forrester Research, said enterprise application integration (EAI) projects cost at least twice as much as high-end ESBs. The licensing costs of those ESBs fall in the $100,000 to $250,000 range, while EAI software can cost $500,000, Gilpin said, adding that some low-end ESB products cost less than $25,000.

Matt Miszewski, Wisconsin's chief information officer, said ESB has been significantly less expensive than EAI technology. The state selected Cape Clear Software's ESB last year. "We got the same performance out of Cape Clear that we got out of the larger EAI suites that were out there," he said.

How do vendors' approaches to ESB differ?

Vendors marketing ESB solutions often have experience in enterprise messaging, application server technology and EAI. Competitors range from market pioneer Sonic to newcomer IBM, which unveiled its ESB strategy last month. Needless to say, approaches to the technology are diverse.

"Each vendor has a different set of components that they are marketing as ESB," Beckley said, adding that some vendors have repackaged older solutions under the ESB label.

Gilpin said his evaluation of ESB technology uncovered more similarities than one might expect. But the presence or absence of a built-in messaging backbone is a significant variable among products, he said.

One camp combines their ESB software with messaging middleware from companies such as IBM and Tibco Software. Gilpin said Cape Clear, Iona Technologies and PolarLake are representative of this category. Such companies tend to emphasize Web services adoption.

Companies in another group, which includes Sonic and Fiorano, embed their own messaging backbones as part of an ESB solution, Gilpin said. Those companies tend to be less aggressive in the implementation of the latest and greatest Web services standards, he said.

The two segments have started to converge, however. Some service-oriented ESB vendors are adding messaging to their products via open source, Gilpin said. The companies built on messaging, meanwhile, are catching up in the Web services department, he added.

The other main split is low-end vs. high-end products. Low-end products, Gilpin said, emphasize ESBs that are lightweight, easy to use and inexpensive. The ESB pioneers typically fall into this category, he said.

High-end products carry higher price tags but may offer additional features such as trading partner management and more robust service orchestration and monitoring, Gilpin said. "Clearly, there are people who want richer business process management," he said.

Are there any open-source options?

Open-source ESB projects represent another twist. The Apache Software Foundation has launched the Apache Synapse ESB project, while Iona contributed technology to Celtix, an open-source ESB hosted by the ObjectWeb Consortium.

Eric Newcomer, Iona's CTO, said the company plans to pursue the open-source Celtix and its commercial Artix ESB. He said he believes open source will help seed small ESB projects. Iona's commercial offering, he added, provides an enterprisewide solution. "There's room for both," Newcomer said.