Karl Reinsch’s Blog

I am often asked to describe the rule engines that Microsoft ships. (The first question being: “Microsoft has rule engines?”) This question frequently comes from folks who know rules, but don’t know .NET. This post is specifically written to answer the question. Should the offerings change in the future, I will update this post as needed.

As always, this is not an official Microsoft statement. Questions about the future directions for these products should be directed to Microsoft.

As of this writing, Microsoft is currently shipping two rule engines. They are aimed at somewhat different audiences as described below.

The first rule engine is called the Microsoft Business Rule Engine (sometimes called “MS BRE” or “BRE”) and it has shipped as part of BizTalk Server since early 2004. BRE has shipped in BizTalk Server 2004, BizTalk Server 2006, BizTalk Server 2006 R2, BizTalk Server 2009 and I’m sure it will be included in the upcoming BizTalk Server 2009 R2.

The second rule engine is part of Windows Workflow Foundation in .NET, it is the Windows Workflow Foundation Rule Engine (sometimes called “Workflow Rules” or “WF Rules”). The WF rule engine originally shipped in late 2006 as part of .NET 3.0. It was also included in .NET 3.5 and will be included in the upcoming .NET 4.0. If you are running Windows 7, Windows Server 2008 R2, Windows Server 2008, or Windows Vista or have installed .NET 3.0 or higher – you already have the WF rule engine on your computer.

Here are some comparisons of these engines written by other folks. Charles Young has written extensively on this topic.

• Charles Young – Comparing WF rules and the Microsoft Business Rule Engine
• Charles Young – BizTalk Server or WF for rules and tracking?
• Charles Young – WF Rules and MS BRE – Comparing Performance
• Stephen Kaufman’s comparison that was presented to the Twin Cities BizTalk User Group. (In my opinion, the portrayal of the agenda in this presentation is inconsistent and needs to be cleaned up.)

If you asked me to summarize differences for a rules specialist, my comments would be along the following lines:

• MS BRE is part of a BizTalk Server, which is a business-oriented server package, while WF Rules is part of the free .NET Framework. (MS BRE may be used standalone outside of BizTalk, but is only licensed with BizTalk.) Both engines provide forward chaining evaluation. WF Rules also provides the option for sequential evaluation.
• MS BRE rules are typically authored in the Rules Composer, while WF Rules are typically authored in Visual Studio. There are partners that provide a more BRMS-like authoring environment. MS BRE has features such as vocabularies and a respository, and is therefore closer to what Gartner defines as a BRMS.
• MS BRE implements the Rete algorithm, while WF Rules does not. MS BRE implements a greedy evaluation strategy, while WF Rules implements a lazy evaluation strategy. The performance profiles are accordingly different – WF “first hit” execution being faster, for example.
• WF does not have assert/retract keywords or a Working Memory, while MS BRE does – so WF Rules requires all objects to be reachable from a common root object (this). (In WF Rules, support for multiple instances is achieved through forward chaining.) WF Rules supports “Else”, while MS BRE does not. MS BRE has some known restrictions around negation-as-failure. MS BRE has special handling for XML and DB fact types.

I would be remiss if I did not mention some Microsoft offerings that apply to related areas:

• Microsoft Solver Foundation – a constraint-solving framework
• Microsoft StreamInsight – a Complex Event Processing engine
• Reactive Framework (Rx) – adds operators such as ForkJoin to .NET

Lastly, I should also point out that the Mono Project is reimplementing Windows Workflow Foundation – including WF Rules.