Advocates of "bottom-up" SOA efforts continue to be heard, even as SOA matures and expands in the enterprise, requiring more enterprise-level management.
Meanwhile, an opposing "top-down" governance approach involves extensive planning and strict policy enforcement. This approach has been faulted for taking much more time to produce results.
Like it or not, there is always a bit of messiness to the way enterprises deploy IT and build applications, said Mahau Ma, VP of Marketing at open source middleware maker MuleSoft. This suggests that enterprise architects really cannot plan for all eventualities but that they actually can stunt growth with rigid top-down SOA programs.
"Any time you've got to spend seven figures on software licenses, roll it out for 24 months and hope you get a big return on the back end, it never seems to pan out that way," said Ma. "You'd like to think there's some architect in the sky that's perfectly planning things out, but from our standpoint that doesn't seem to be reality."
MuleSoft, makers of the Mule ESB, recently released management tools said to support the bottom-up approach to SOA management. In turn, top SOA governance tool vendors promote the long view on SOA management.
"Building a SOA from the bottom up may work at first, but at some point you're going to have to provide service-level agreements (SLAs) to the business," said Jignesh Shah, VP of business infrastructure products and solutions at Software AG.
At that point, he said, an enterprise will need a top-down strategy. "To me, bottom-up is more about everyone in their own silos figuring out what services they should build and then, when needed, they see the opportunity for things like reuse and evolving services," said Shah. "That's a very reactive approach to building out your SOA portfolio."
Be careful not to consider the bottom-up approach a type of "real governance," warns Jason Bloomberg, analyst with ZapThink, Inc. Governance means enforcing organizational policies all the way down through IT, he said, and cannot be accomplished by simply adding more tools.
"MuleSoft's focus is on governance tooling and their governance tools are suitable for small departmental efforts, but not for enterprise SOA efforts," said Bloomberg. "So I'm not surprised they don't see the importance of real governance—what some people call 'top-down.'"
Meanwhile, suggests MuleSoft's Ma, developers are going to do what they're going to do, and it is wise to give them the tooling to keep them out of trouble. When developers don't have all of their policies set by the business side, Ma said, IT can more quickly react to changing business needs.
Consultant says bottom-up SOA strategy appropriate to start
In some areas where enterprises have been slower to adopt SOA, most adopters tend to go with a bottom-up approach, said George Goosen, an independent SOA consultant working in South Africa.
Often enough, such services built with a bottom-up mentality require additional work and orchestration in order to be exposed enterprise-wide, counters Alistair Farquharson, CTO of SOA Software, Inc.
"We see that the scope of bottom-up-designed services is limited to within a development group," said Farquharson. "Services that are designed from the top down with a broader constituency in mind are exposed and shareable across the enterprise."
Implementer Goosen agrees that as the architecture grows more complex, such an approach often becomes necessary. "When your primary focus is just to integrate, bottom-up suits that because you can implement services in a relatively small footprint in the business with relatively good results," said Goosen.
"And because you get the good results on the first couple of services, it becomes kind of like a bushfire, where you have thousands of services that may or may not be redundant," he said.
Choosing an SOA governance strategy depends on business–IT relations
Maturity of SOA programs and the extent of SOA adoption is an issue when comparing top-down and bottom-up SOA governance and management approaches. A recent Gartner report found that the SOA Governance market expanded 17.5% in 2009, a sign to some that enterprise SOA is maturing.
"As people start doing SOA, the technology on its own is not enough and you need to put some governance into place," said Fabrizio Biscotti, Gartner analyst and author of the report. "You don't start with governance technologies. Generally it's something you put aside the SOA implementation technologies, or you buy it after you start doing SOA."
So how does an enterprise architect choose between a top-down approach and a bottom-up approach to SOA governance strategy? In the end it comes down to the relationship between business and IT, said Hariharan VG, senior architect at consultancy MGL Americas.
"If an enterprise looking for SOA adoption has a strong vision and roadmap, then the top-down approach is the best fit," said Hariharan. "If it does not have an IT strategy at the enterprise level and no long term vision, IT can go for a bottom-up approach to realize and showcase the SOA benefits."