Rules engines will become more important as companies look to make their IT systems more flexible, according to analyst Gartner.

Jim Sinur, senior research director at Gartner, told delegates at last week's European Business Rules Conference in Amsterdam that, while rules might not be considered "trendy", their importance is growing.

Business rules began as code within applications that controlled the outcome of 'if' and 'when' scenarios.

But as users demanded more flexible applications, rules were abstracted into a separate management system, or 'rules engine', allowing programmers to manipulate the code that controls an application's rules.

"The business rules sector was in a trough of disillusionment from 1998 to 2001. We are now seeing significant growth here," said Sinur.

Software vendors have made it easier to manipulate and manage rules that govern business processes by introducing methodologies and standards, and embedding rules engines in products, he added.

And customers are keen to move to service-oriented architectures capable of rapidly implementing process change by using rules-based engines.

Sinur said the recent market trend towards business process management and its workflow-modelling components has masked the increasing importance of rules.

He pointed to Microsoft's middleware product BizTalk 2004, which contains a rules engine for the first time. And he predicted that rules management technology would be increasingly embedded into other vendors' products.

Gartner estimates the $500m rules-based IT market will double to $1bn by 2007.

"The notion of using rules engines is not dead," said Sinur.

"Just as yesterday we separated the client-server interface from processes and from data, we are today separating rules from workflows and from services."