I have been asked to start exploring a Activiti tool for some client demo.
The demo will also have JBoss Drools with which Activiti will be integrated.
I am new to both of these tools and business process world, so excuse me if the question is dumb.
The question is why do you need Drools? Isn't Activiti enough for the job?
Both of them have conditional elements so why do you need Activiti on top of drools?
This question doesn't quite fit the purpose of StackOverflow, so don't be surprised if you get a few flags. But I'll try to give a short answer.
Activity is a workflow engine, Drools is a business rules engine. They serve two different purposes.
Workflow engines are useful when you have a flow of actions of different actors that need to be controlled programmatically.
Rules engines are useful when you have business rules for executing some task automatically that you want to describe in a declarative way.
Both purposes are orthogonal to each other, meaning that the problem you have to solve may require none, just one, or both of them.
Imagine a workflow where a customer reports an incident, some experts have to work on it, and finally a bill gets produced, but no heavy algorithms are behind those tasks. That might be supported by a workflow engine without a rules engine.
Imagine a complex price model for a product, like cars having all sorts of special features that may be ordered. (Hifi speakers cost 400 €, except if the executive version of the car is ordered, where they only cost 200 € if ordered in combination with smartphone adapter...) Here a rules engine may be useful, although nobody talked about a workflow, so no workflow engine is needed.
Imagine the first example (incident workflow) together with a complex billing scheme. Here both tools may be used.
I wonder why these two types of tools are in some places described as perfectly fitting together. (Maybe this kind of claim motivated your question.) They serve two different purposes, and whether you need them both depends on the problem you have to solve.
I have a question about WWF, I'm working on a webbased ERP project which is a modular application ofcourse.
I'm looking for a way to create an engine for wokflows in the framwrok so modules can rely on it and based on this engine create their workflows.As I see there should be 3 kind of workflows (Human for confirmation of info among the organization, Business for handling business flows such as calculating personnel income based on the different factors and UI workflow for handling chain of usercontrols based on a cartable (dashboard) )
I need some help on handling this and if there is any problem in my insight I wonder to be informed.
This is extremely broad and without more context hard to answer.
WorkFlow can be used in conjunction with e.g. SharePoint to take care of the Human part of a workflow such as creating a document or marking it as OK.
WF can be deployed as a service and supports the interaction with other (web)services to support modularity.
What goals can be accomplished using a Rules Engine?
A Rules Engine is typically a component in software that is used to validate business rules at runtime.
They're often used in order to be able to easily change business rules without having to recompile/redeploy software. Rules can easily be stored in a corporate database, and sometimes even edited by less technical users who understand the business rules much more effectively.
For example, a mortgage company may need to change its criteria for approving a mortgage every week. By using a rules engine, you can easily create very complex criteria that can be modified without having to "program" the logic into the software. Say, this week, the base credit score shifts, you just adjust that rule in the chain of rules. Then, tomorrow, when the minimum income percentage for requiring PMI given a 90% equity rate shifts, you can just put that "rule" in place.
To add to #Reed Copsey's answer. Most rule engines keep their rules in external files that can be modified by business analysts or end users. Drools is one such solution.
In most cases the Rules being processed are at the business layer, it is possible to look at a firewall as a rule engine of sorts, another common type of rule engine is based on high level domain specific languages for transaction processing and decision making.
There are a number of companies that produce appliances, and web transactions as a service to. These give the analysts tools to form complex decision trees and expert systems without having to do the grunt work of the developer, thanks to the magic of EGL most of the translation is done by modeling tools that can stub and generate code and valid end points to meet the "business" needs automagically.
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I have a pretty decent list of the advantages of using a Rules Engine, as well as some reasons to use them, what I need is a list of the reasons why you should NOT use a Rules Engine
The best I have so far is this:
Rules engines are not really intended to handle workflow or process
executions nor are workflow engines or process management tools
designed to do rules.
Any other big reasons why you should not use them?
I will give 2 examples from personal experience where using a Rules Engine was a bad idea, maybe that will help:-
On a past project, I noticed that the rules files (the project used Drools) contained a lot of java code, including loops, functions etc. They were essentially java files masquerading as rules file. When I asked the architect on his reasoning for the design I was told that the "Rules were never intended to be maintained by business users".
Lesson: They are called "Business Rules" for a reason, do not use rules when you cannot design a system that can be easily maintained/understood by Business users.
Another case; The project used rules because requirements were poorly defined/understood and changed often. The development team's solution was to use rules extensively to avoid frequent code deploys.
Lesson: Requirements tend to change a lot during initial release changes and do not warrant usage of rules. Use rules when your business changes often (not requirements). Eg:- A software that does your taxes will change every year as taxation laws change and usage of rules is an excellent idea. Release 1.0 of an web app will change often as users identify new requirements but will stabilize over time. Do not use rules as an alternative to code deploy.
I get very nervous when I see people using very large rule sets (e.g., on the order of thousands of rules in a single rule set). This often happens when the rules engine is a singleton sitting in the center of the enterprise in the hope that keeping rules DRY will make them accessible to many apps that require them. I would defy anyone to tell me that a Rete rules engine with that many rules is well-understood. I'm not aware of any tools that can check to ensure that conflicts don't exist.
I think partitioning rules sets to keep them small is a better option. Aspects can be a way to share a common rule set among many objects.
I prefer a simpler, more data driven approach wherever possible.
The one poit I've noticed to be "the double edged sword" is:
placing the logic in hands of non technical staff
I've seen this work great, when you have one or two multidisciplinary geniuses on the non technical side, but I've also seen the lack of technicity leading to bloat, more bugs, and in general 4x the development/maintenance cost.
Thus you need to consider your user-base seriously.
I'm a big fan of Business Rules Engines, since it can help you make your life much easier as a programmer. One of the first experiences I've had while working on a Data Warehouse project was to find Stored Procedures containing complicated CASE structures stretching over entire pages. It was a nightmare to debug, since it was very difficult to understand the logic applied in such long CASE structures, and to determine if you have an overlapping between a rule at page 1 of the code and another from page 5. Overall, we had more than 300 such rules embedded in the code.
When we've received a new development requirement, for something called Accounting Destination, which was involving treating more than 3000 rules, i knew something had to change. Back then I've been working on a prototype which later on become the parent of what now is a Custom Business Rule engine, capable of handling all SQL standard operators. Initially we've been using Excel as an authoring tool and , later on, we've created an ASP.net application which will allow the Business Users to define their own business rules, without the need of writing code. Now the system works fine, with very few bugs, and contains over 7000 rules for calculating this Accounting Destination. I don't think such scenario would have been possible by just hard-coding. And the users are pretty happy that they can define their own rules without IT becoming their bottleneck.
Still, there are limits to such approach:
You need to have capable business users which have an excellent understanding of the company business.
There is a significant workload on searching the entire system (in
our case a Data Warehouse), in order to determine all hard-coded
conditions which make sense to translate into rules to be handled by
a Business Rule Engine. We've also had to take good care that these
initial templates to be fully understandable by Business Users.
You need to have an application used for rules authoring, in which
algorithms for detection of overlapping business rules is implemented. Otherwise you'll end up with a big mess, where no one understands anymore the results they get.
When you have a bug in a generic component like a Custom Business Rule Engine, it can be very difficult to debug and involve extensive tests to make sure that things that worked before also work now.
More details on this topic can be found on a post I've written: http://dwhbp.com/post/2011/10/30/Implementing-a-Business-Rule-Engine.aspx
Overall, the biggest advantage of using a Business Rule Engines is that it allows the users to take back control over the Business Rule definitions and authoring, without the need of going to the IT department each time they need to modify something. It also the reduces the workload over IT development teams, which can now focus on building stuff with more added value.
Cheers,
Nicolae
GREAT article on when not to use a rules Engine...(as well as when to use one)....
http://www.jessrules.com/guidelines.shtml
Another option is if you have a linear set of rules that only apply once in any order to get an outcome is to create a groovy interface and have developers write and deploy these new rules. The advantage is that it is wickedly fast because normally you would pass the hibernate session OR jdbc session as well as any parameters so you have access to all your apps data but in an efficient manner. With a fact list, there can be alot of looping/matching that really can slow the system down.....It's another way to avoid a rules engine and be able to be deployed dynamically(yes, our groovy rules were deployed in a database and we had no recursion....it either met the rule or it didn't). It is just another option.....oh and one more benefit is not learning rules syntax for incoming developers. They have to learn some groovy but that is very close to java so the learning curve is much better.
It really depends on your context. Rules engine have their place and the above is just another option if you have rules on a project that you may want to deploy dynamically for very simplified situations that don't require a rules engine.
BASICALLY do NOT use a rules engine if you have a simple ruleset and can have a groovy interface instead.....just as dynamically deployable and new developers joining your team can learn it faster than the drools language.(but that's my opinion)
In my experience, rules engines work best when the following are true:
Well-defined doctrine for your problem domain
High quality (preferably automated) data to help drive most of your inputs
Access to subject matter experts
Software developers with experience creating expert systems
If any of these four traits are missing, you still might find a rules engine works for you, but every time I've tried it with even 1 missing, I've run into trouble.
That's certainly a good start. The other thing with rules engines is that some things are well-understood, deterministic, and straight-forward. Payroll withholding is (or use to be) like that. You could express it as rules that would be resolved by a rules engine, but you could express the same rules as a fairly simple table of values.
So, workflow engines are good when you're expressing a longer-term process that will have persistent data. Rules engines can do a similar thing, but you have to do a lot of added complexity.
Rules engines are good when you have complicated knowledge bases and need search. Rules engines can resolve complicated issues, and can be adapted quickly to changing situations, but impose a lot of complexity on the base implementation.
Many decision algorithms are simple enough to express as a simple table-driven program without the complexity implied by a real rules engine.
I would strongly recommend business rules engines like Drools as open source or Commercial Rules Engine such as LiveRules.
When you have a lot of business policies which are volatile in nature, it is very hard to maintain that part of the core technology code.
The rules engine provides a great flexibility of the framework and easy to change and deploy.
Rules engines are not to be used everywhere but need to used when you have lot of policies where changes are inevitable on a regular basis.
I don't really understand some points such as :
a) business people needs to understand business very well, or;
b) disagreement on business people don't need to know the rule.
For me, as a people just touching BRE， the benefit of BRE is so called to let system adapt to business change, hence it's focused on adaptive of change.
Does it matter if the rule set up at time x is different from the rule set up at time y because of:
a) business people don't understand business, or;
b) business people don't understand rules?
What is the most typical structure of business where you want to develop several web services? Should one establish a company for each of them or keep under one? I would like to hear your experiences maintaining such situation, keeping in mind the global focus.
By far the two most critical sets of issues determining the answer to this question are legal and financial (including, but not mainly, accounting). So it's hard to see how this question fits with the intent of this site.
It is advised to provide more background information on the topic. Business plans for SaaS companies can range from large cloud computing service vendors (with integrated solutions) and up to business analytics providers targeting specific market niche.
Business is a bit like programming: Keep It Simple (Stupid). Do not create multiple companies, unless there is a good reason to do it.
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Thanks