I'm architecturing a Multi Agent System (MAS) framework to describe Beliefs-Desires-Intents (BDI) agents in Haskell (i.e. agents are concurrent, communicating monadic actions).
I searched on the web throughly but I wasn't able to find any reference on similar works, apart from a technical report of an unfinished work, Specifying and Controlling Agents in Haskell.
Do you know about any existing implementation or research paper dealing with BDI agents that can be defined in Haskell or in any other functional language, please?
My aim is to find possible related works, everything that could manage a system of concurrent intelligent agents written in a functional language. I don't need anything specific, I just want to find out whether my work has something in common with existing approaches.
edit: I managed to find a reference to Clojure, a lisp dialect that supports a form of agent programming very close to the actor model, but it's not meant to directly support BDI agents (one should implement another layer on top of it to get the BDI part done I guess).
To sum up, it doesn't seem like there are proposals for BDI-style communicating agents described by means of functional languages, so together with a friend/colleague of mine we collected info about related work, put together some ideas, and we wrote a short position paper that I will present at the DALT2012 workshop. It's a really preliminary work, so do not expect too much from it, but I think in the future it may evolve in something interesting.
Alessandro Solimando, Riccardo Traverso. Designing and Implementing a Framework for BDI-style Communicating Agents in Haskell. DALT 2012, Workshop notes, pages 108--112.
EDIT:
I later found this project on GitHub, which uses free monads (whatever that means, I don't know about them) to provide a framework for multi-agent systems: https://github.com/fizruk/free-agent.
I would like to create a set of domain objects in multiple languages, so that I can target different platforms. I have been looking at external DSLs as a way to define a language for my domain, and then potentially writing adapters that generate code for the languages I'm interested in targeting. Is this the best way to solve this problem? Or is it just simpler to maintain multiple versions of the project?
I think that Apache Thrift delivers what you are asking for.
Sorry for late answer, but as you mention C# being your main language, this practically fully supported Visual Studio based technology is exactly what you are looking for.
You have to understand what you want to abstract with your DSLs, but the multiple-platform support is trivial on top of that.
Disclaimer: This is our technology, but it's publicly open and it solves exactly the problem presented in the question.
http://abstraction.codeplex.com/
Note! Mind the very "alpha" stage of the current download, I suggest you skip the zipped download and grab the latest source. I am updating better construct in relatively near future. Check out the "Context" implementation in "Production/Dev/AbstractionTemplate" solution.
It is difficult to be helpful without understanding what you are planning to use your DSL for.
Is portability your main problem here?
To succesfully target these different platforms, you will probably have to maintain plaftorm-specific layers anyway (generated or not).
If you plan to write your whole application in your DSL, then use your own compiler to transform it into runnable code for each platform, well it is most probably a bad idea, too complex and overengineered.
However, if you have a well-defined chunk of platform-independent logic, then a DSL is a good choice. Just write an interpreter for it on each target platform (provided that performance is not critical, this is also simpler and easier than generating code).
What is the best way to create multiple language versions of a domain?
This is (was?) somehow the idea of Model Driven Architecture (MDA). Quoting Model-driven architecture from Wikipedia:
The Model-Driven Architecture approach
defines system functionality using a
platform-independent model (PIM) using
an appropriate domain-specific
language (DSL).
Then, given a platform definition
model (PDM) corresponding to CORBA,
.NET, the Web, etc., the PIM is
translated to one or more
platform-specific models (PSMs) that
computers can run. This requires
mappings and transformations and
should be modeled too.
The PSM may use different Domain
Specific Languages (DSLs), or a
General Purpose Language (GPL) like
Java, C#, PHP, Python, etc. Automated tools generally
perform this translation.
Depending on the complexity of your domain and the availability of a MDA Tool, this might be an option (with a lower implementation cost).
See also
MDA: Nice idea, shame about the ...
Language Workbenches and Model Driven Architecture
UML vs. Domain-Specific Languages
DSL in the context of UML and GPL
UML or DSL: Which Bear Is Best? (be sure to read this one)
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I'm currently faced with a very unusual design problem, and hope that a developer wiser than myself might be able to offer some insight.
Background
Without being too specific, I've been hired by a non-profit organisation to assist with the redevelopment of their legacy, but very valuable (in terms of social value) software. The development team is unlike any I've encountered in my time as a software developer, and is comprised of a small number of developers and a larger group of non-programming domain experts. What makes the arrangement unusual is that the domain experts (lets call them content creators), use custom tooling, some of which is based around a prolog expert system engine, to develop web based software components/forms.
The Problem
The system uses a very awkward postback model to perform logical operations server side and return new forms/results. It is slow, and prone to failure. Simple things, like creating html forms using the existing tooling is much more arduous than it should be. As the demand for a more interactive, and performant experience grows, the software developers are finding increasingly that they have to circumvent the expert system/visual tooling used by the content creators, and write new components by hand in javascript. The content creators feel increasingly that their hands are tied, as they are now unable to contribute new components.
Design approach: Traditional/Typical
I have been advocating for the complete abandonment of the previous model and the adoption of a typical software development process. As mentioned earlier, the project has naturally evolved towards this as the non-programmatic development tooling has become incapable of meeting the needs of the business.
The content creators have a very valuable contribution to make however, and I would like to see them focusing on formally specifying the expected behaviour of the software with tools like Cucumber, instead of being involved in implementation.
Design approach: Non-programmatic
My co-worker, who I respect a great deal and suspect is far more knowledgeable than me, feels that the existing process is fine and that we just need to build better tooling. I can't help but feel however that there is something fundamentally flawed with this approach. I have yet to find one instance, either historical or contemporary where this model of software development has been successful. COBOL was developed with the philosophy of allow business people/domain experts to write applications without the need for a programmer, and to my mind all this did was create a new kind of programmer - the COBOL programmer. If it was possible to develop effective systems allowing non-programmers to create non-trivial applications, surely the demand for programmers would be much lower? The only frameworks that I am aware of that roughly fit this model are SAP's Smart Forms and Microsoft's Dynamix AX - both of which are very domain specific ERP systems.
DSLs, Templating Languages
Something of a compromise between the two concepts would be to implement some kind of DSL as a templating language. I'm not even sure that this would be successful however, as all of the content creators, with one exception, are completely non technical.
I've also considered building a custom IDE based on Visual Studio or Net Beans with graphical/toolbox style tooling.
Thoughts?
Is non-programmatic development a fools errand? Will this always result in something unsatisfactory, requiring hands on development from a programmer?
Many thanks if you've taken the time to read this, and I'd certainly appreciate any feedback.
You say:
Something of a compromise between the
two concepts would be to implement
some kind of DSL as a templating
language. I'm not even sure that this
would be successful however, as all of
the content creators, with one
exception, are completely non
technical.
Honestly, this sounds like exactly the approach I would use. Even "non-technical" users can become proficient (enough) in a simple DSL or templating language to get useful work done.
For example, I do a lot of work with scientific modeling software. Many modelers, while being much more at home with the science than with any form of engineering, have been forced to learn one or more programming languages in order to express their ideas in a way they can use. Heck, as far as I know, Fortran is still a required course in order to get a Meteorology degree, since all the major weather models currently in use are written in Fortran.
As a result, there is a certain community of "scientific programming" which is mostly filled with domain experts with relatively little formal software engineering training, expertise, or even interest. These people are more at home with languages/platforms like Matlab, R, and even Visual Basic (since they can use it to script applications like Excel and ESRI ArcMap). Recently, I've seen Python gaining ground in this space as well, mainly I think because it's relatively easy to learn.
I guess my point is that I see strong parallels between this field and your example. If your domain experts are capable of thinking rigorously about their problems (and this may not be the case, but your question is open-ended enough that it might be) then they are definitely capable of expressing their ideas in an appropriate domain-specific language.
I would start by discussing with the content creators some ideas about how they would like to express their decisions and choices. My guess would be that they would be happy to write "code" (even if you don't have to call it code) to describe what they want. Give them a "debugger" (a tool to interactively explore the consequences of their "code" changes) and some nice "IDE" support application, and I think you'll have a very workable solution.
Think of spreadsheets.
Spreadsheets are a simple system that allows non-technical users to make use of a computer's calculation abilities. In doing so, they have opened up computers to solve a great number of tasks which normally would have required custom software developed to solve them. So, yes non-programmatic software development is possible.
On the other hand, look at spreadsheets. Despite their calculational abilities you really would not want as a programmer to have to develop software with them. In the end, many of the techniques that make programming languages better for programmers make them worse for the general population. The ability to define a function, for example, makes a programmer's life much easier, but I think would confuse most others.
Additionally, past a certain point of complexity trying to use a spreadsheet would be a real pain. The spreadsheet works well within the realm for which it was designed. Once you stray too far out that, its just not workable. And again, its the very tools programmers use to deal with complexity which will prevent a system being both widely usable and sufficiently powerful.
I think that for any given problem area, you could develop a system that allows the experts to specify a solution. It will be much harder to develop that system then to solve the problem in the first place. However, if you repeatedly have similiar problems which the experts can develop solutions for, then it might be worthwhile.
I think development by non-developers is doomed to failure. It's difficult enough when developers try it. What's the going failure rate? 50% or higher?
My advice would be to either buy the closest commercial product you can find or hire somebody to help you develop a custom solution with your non-developer maintenance characteristics in mind.
Being a developer means keeping a million details in mind at once and caring about details like version control, deployment, testing, etc. Most people who don't care about those things quickly tire of the complexity.
By all means involve the domain experts. But don't saddle them with development and maintenance as well.
You could be putting your organization at risk with a poorly done solution. If it's important, do it right.
I don't believe any extensive non-programmer solution is going to work. Programming is more than language, it's knowing how to do things reasonably. Something designed to be non-programmer friendly will still almost certainly contain all the pitfalls a programmer knows to avoid even if it's expressed in English or a GUI.
I think what's needed in a case like this is to have the content creators worry about making content and an actual programmer translate that into reasonable computer code.
I have worked with two ERP systems that were meant for non-programmers and in both cases you could make just about every mistake in the book with them.
... Simple things, like creating html forms using the existing tooling is much more arduous than it should be...
More arduous for whom? You're taking a development model that works (however badly) for the non-programming content creators, and because something is arduous for someone you propose to replace that with a model where the content creators are left out in the cold entirely? Sounds crazy to me.
If your content creators can learn custom tooling built around a Prolog rules engine, then they have shown they can learn enough formalism to contribute to the project. If you think other aspects of the development need to be changed, I see only two honorable choices:
Implement the existing formalism ("custom tooling") using the new technology that you think will make things better in other ways. The content creators contribute exactly as they do now.
Design and implement a domain-specific language that handles the impedance mismatch between what your content creators know and can do and the way you and other developers think the work should be done.
Your scenario is a classic case where a domain-specific language is appropriate. But language design is not easy, especially when combined with serious usability questions. If you are lucky you will be able to hire someone to help you who is expert in both language design and usability. But if you are nonprofit, you probably don't have the budget. In this case one possibility is to look for help from another nonprofit—a nearby university, if you have one.
I'd advise you to read this article before attempting to scrap the whole system. I look at it this way. What changed to prompt the redevelopment? Your domain experts haven't forgotten how to use the original system, so you already have some competent "COBOL programmers" for your domain. From your description, it sounds like mostly the performance requirements have changed, and possibly a greater need for web forms.
Therefore, the desired solution isn't to change the responsibilities of the domain experts, it's to increase the performance and make it easier to create web forms. You have the advantage of an existing code base showing exactly what your domain experts are capable of. It would be a real shame not to use it.
I realize Prolog isn't exactly the hottest language around, but there are faster and slower implementations. Some implementations are designed mostly for programmer interactivity and are dynamically interpreted. Some implementations create optimized compiled native code. There are also complex logical programming techniques like memoization that can be used to enhance performance, but probably no one learns them in school anymore. A flow where content creators focus on creating new content and developers focus on optimization could be very workable. Also, Prolog is ideally suited for the model layer, but not so much for the view layer. Moving more of your view layer to a different technology could really pay off.
In general though, 2 thoughts:
You cannot reduce life to algorithms. Everything we know (philosophically, scientifically) and experience demonstrates this. (Sorry, Dr. Minsky).
That said, a Domain-Specific tool that allows non-programmers to express a finite language is definitely doable as several people have given examples. Another example of this type of system is Mathematica and especially Simulink which are used very successfuly over a range of applications. However, the failure of Expert Systems, Fuzzy logic, and Japan's Fifth Generation computer project of the 80's to take-off demonstrate the difficulty in doing this.
Labview is a very successful none programatic programming environment.
What an interesting problem.
I would have to ultimately agree with you, and disagree with your colleague.
The philosophy and approach of Domain Driven Development/Design exists exactly for your purposes, in that it puts paramount importance on the specific knowledge of the experienced domain experts, and on communicating that knowledge to talented software developers.
See, in your issue, there are two distinct things. The domain, and the software. The domain should be understood and specified first and foremost without software development in mind.
And then the transformation to software happens between the communication between domain experts and programmers.
I think trying to build "programming" tools for domain experts is a waste of time.
In Domain Driven Development your domain experts will continue to be important, and you'll end up with better software.
In your colleague's approach you're trying to replace programmers with tool.... maybe in the future, like, start trek future, that will be possible, but today I don't think so.
I am currently struggling with a similar problem in trying to enable healthcare providers to write rules for workflows, which isn't easy because they aren't programmers. You're a programmer not because you went to programming school -- you're a programmer because you think like a programmer. Fortunately, most hospitals have some anesthesiologist or biomedical engineer who thinks like a programmer and can manage to program. The key is to give the non-programmers-who-think-like-programmers a language that they can learn and master.
In my case, I want doctors to be able to formulate simple rules, such as: "If a patient's temperature gets too low, send their doctor a text message". Of course it's more complicated than that because the definition of "too low" depends on the age of the patient, a patient may have many doctors, and so on, but a smart doctor will be able to figure out those rules. The real issue is that the temperature sensor will often fall off the patient and read ambient temperature, meaning that the rule is useless unless you can figure out how to determine that the thermometer is actually reading the patient's temperature.
The big problem I have is that, while it's relatively easy to create a DSL so that doctors can express IF [temperature] [less-than] [lookup-table [age]] THEN [send-text-message], it's much harder to create one that can express all the different heuristics you might need to try before coming up with the right way to make sure the reading is valid.
In your case, you may want to consider how VB became popular: It has a form drawing tool that anybody can easily use to draw forms and set properties on form items. Since not everything can be specified by form properties and data binding, there's a code-behind mode that lets you do complex logic. But to make the tool accessible to beginning programmers, the language is BASIC, so users didn't have to learn about pointers, memory allocation, or data structures.
While you probably wouldn't want to give your users VB, you might consider a hybrid approach. You would have one "language" (it could be graphical, like VB's form designer or Labview) where inexperienced users can easily do the simple stuff, and another language to enable expert users to do the complicated stuff.
I had this as a comment previously but I figured it deserved more merit.
There are definitely a number of successful 'non-programmatic' tools around, off hand I can think of Labview, VPL and graph based (edit: I just noticed this link has more far more than just shaders on it) shaders which are prevalent in 3D applications.
Having said that, I don't know of any which are suited to web based dev (which appears to be your case).
I dout very much the investment on developing such tools would be worth it (unless maybe you could move to sell it as a product as well).
I agree with you - non-technical people will not be able to program anything non-trivial.
Some products try to create what's basically a really simple programming language. The problem is that programming is an aptitude as well as a skill. It takes a certain kind of mindset to think in the sort of logic used by computers, which just can't be abstracted away by any programming language (at least not without without making assumptions that it can't safely make).
I've seen this in action with business people trying to construct workflows in MS Dynamics CRM. Even though the product was clearly intended to allow them to do it without a programmer they just couldn't figure out how to make a loop or an if-else condition work, no matter how "friendly" the UI tried to make it. I watched in amazement as they struggled with something that seemed completely self-obvious to me. After a full day (!) of this they managed to produce a couple of very basic workflows that worked in some cases, but didn't handle edge cases like missing values or invalid data. It was basically a complete waste of time.
Granted, Dynamics CRM isn't exactly the epitome of user-friendliness, but I saw enough to convince me that this is, indeed, a fool's errand.
Now, if your users are not programmers, but still technical people they might be able to learn programming, but that's another story - they've really become "new programmers" rather than "non-programmers" then.
This is a pretty philosophical topic and difficult to answer for every case, but in general...
Is non-programmatic development a fools errand?
Outside of a very narrow scope, yes. Major software vendors have invested billions over the years in creating various packages to try to let non-technical users create & define workflows and processes with limited success. Your best bet is to take advantage of what has been done in that space rather than trying to re-invent it.
Edit:
Sharepoint, InfoPath, some SAP stuff are the examples I'm talking about. As I said above, "a very narrow scope". It's possible to let non-programmers create workflows, complex forms, some domain processes, but that's it. Anything more general-purpose is simply trying to make non-programmers into programmers by giving them very crude tools.
Non programatic software development IS feasable, as long as you are realistic about what non-developers can reasonaby achieve - its all about a compromise between capability and ease of use.
The key is to break the requirements down cleanly into things that the domain experts need to be able to do, and spend time implementing those features in a foolproof way - The classic mistake is to try to let the system to do too much.
For example suppose you want domain experts to be able to create a form with a masked text input:
Most developers will look at that requirement and create a fancy control which accepts some sort of regular expression and lets the domain expert do anything.
This is the classic developer way of looking at things, however it's likely that your domain expert does not understand regular expressions and the developer has missed the point of the reqirement which was for the domain expert to be able to create this form.
A better solution might have been to create a control that can be confgiured to mask either Email addresses or telephone numbers.
Yes this control is far less capable than the first control, and yes the domain experts have to ask developers to extend it when they want to be able to mask to car registration numbers, however the domain experts are able to use it.
It seems that the problem is of organizational nature and cannot be solved by technical means alone.
The root is that content creators are completely non-technical, yet have to perform inherently technical tasks of designing forms and writing Prolog rules. Various designers and DSLs can alleviate their problems, but never solve them.
Either reorganize system and processes so knowledge carriers actually enter knowledge - nothing else; or train content creators to perform necessary development with existing tools or may be DSLs.
Non-programmatic development can save from low-level chores, but striving to set up system once and let users indefinitely and unrestrictedly expand it is certainly a fools errands.
Computer games companies operate like this all the time, so far as I can tell: a few programmers and a lot of content creators who need to be able to control logic as well (like level designers).
It's also probably a healthy discipline to be able to separate your code from the data and rules driving it if you can.
I'm therefore with your colleague, but of course the specifics may not make this general solution appropriate!
Can anyone give me an example of successful non-programmer, 5GL (not that I am sure what they are!), visual, 0 source code or similar tools that business users or analysts can use to create applications?
I don’t believe there are and I would like to be proven wrong.
At the company that I work at, we have developed in-house MVC that we use to develop web applications. It is basically a reduced state-machine written in XML (à la Spring WebFlow) for controller and a simple template based engine for presentation. Some of the benefits:
dynamic nature: no need to recompile to see the changes
reduced “semantic load”: basically, actions in controller know only “If”. Therefore, it is easy to train someone to develop apps.
The current trend in the company (or at least at management level) is to try to produce tools for the platform that require 0 source code, are visual etc. It has a good effect on clients (or at least at management level) since:
they can be convinced that this way they will need no programmers or at least will be able to hire end-of-the-lather programmers that cost much less than typical programmers.
It appears that there is a reduced risk involved, since the tool limits the implementer or user (just don’t use the word programmer!) in what he can do, so there is a less chance that he can introduce error
It appears to simplify the whole problem since there seems to be no programming involved (notoriously complex). Since applications load dynamically, there is less complexity then typically associated with J2EE lifecycle: compile, package, deploy etc.
I am personally skeptic that something like this can be achieved. Solution we have today has a number of problems:
Implementers write JavaScript code to enrich pages (could be solved by developing widgets). Albeit client-side, still a code that can become very complex and result in some difficult bugs.
There is already a visual tool, but implementers prefer editing XML since it is quicker and easier. For comparison, I guess not many use Eclipse Spring WebFlow plug-in to edit flow XML.
There is a very poor reuse in the solution (based on copy-paste of XML). This hampers productivity and some other aspects, like fostering business knowledge.
There have been numerous performance and other issues based on incorrect use of the tools. No matter how reduced the playfield, there is always space for error.
While the platform is probably more productive than Struts, I doubt it is more productive than today’s RAD web frameworks like RoR or Grails.
Verbosity
Historically, there have been numerous failures in this direction. The idea of programs written by non-programmers is old but AFAIK never successful. At certain level, anything but the power of source code becomes irreplaceable.
Today, there is a lot of talk about DSLs, but not as something that non-programmers should write, more like something they could read.
It seems to me that the direction company is taking in this respect is a dead-end. What do you think?
EDIT: It is worth noting (and that's where some of insipiration is coming from) that many big players are experimenting in that direction. See Microsoft Popfly, Google Sites, iRise, many Mashup solutions etc.
Yes, it's a dead end. The problem is simple: no matter how simple you make the expression of a solution, you still have to analyze and understand the problem to be solved. That's about 80-90% of how (most good) programmers spend their time, and it's the part that takes the real skill and thinking. Yes, once you've decided what to do, there's some skill involved in figuring out how to do that (in a programming language of your choice). In most cases, that's a small part of the problem, and the least open to things like schedule slippage, cost overrun or outright failure.
Most serious problems in software projects occur at a much earlier stage, in the part where you're simply trying to figure out what the system should do, what users must/should/may do which things, what problems the system will (and won't) attempt to solve, and so on. Those are the hard problems, and changing the environment to expressing the solution in some way other that source code will do precisely nothing to help any of those difficult problems.
For a more complete treatise on the subject, you might want to read No Silver Bullet - Essence and Accident in Software Engineering, by Frederick Brooks (Included in the 20th Anniversary Edition of The Mythical Man-Month). The entire paper is about essentially this question: how much of the effort involved in software engineering is essential, and how much is an accidental result of the tools, environments, programming languages, etc., that we use. His conclusion was that no technology was available that gave any reasonable hope of improving productivity by as much as one order of magnitude.
Not to question the decision to use 5GLs, etc, but programming is hard.
John Skeet - Programming is Hard
Coding Horror - Programming is Hard
5GLs have been considered a dead-end for a while now.
I'm thinking of the family of products that include Ms Access, Excel, Clarion for DOS, etc. Where you can make applications with 0 source code and no programmers. Not that they are capable of AI quality operations, but they can make very usable applications.
There will always be "real" languages to do the work, but we can drag and drop the workflow.
I'm using Apple's Automator which allows users to chain together "Actions" exposed by the various applications on their systems.
Actions have inputs and/or outputs, some have UI elements and basic logic can be applied to the chain.
The key difference between automator
and other visual environments is that
the actions use existing application
code and don't require any special
installation.
More Info > http://www.macosxautomation.com/automator/
I've used it to "automate" many batch processes and had really great results (surprises me every time). I've got it running builds and backups and whenever i need to process a mess of text files it comes through.
I would love to know whether iHook or Platypus (osx wrapper builders for shell scripts) could let me develop plugins in python ....
There is definitely room for more applications like this and for more support from OSX application developers but the idea is sound.
Until there's major support there aren't many "actions" available, but a quick check on my system just showed me an extra 30 that i didn't know i had.
PS. There was another app for OS-preX called "Filter Tops" which had a much more limited set of plugins.
How about Dabble DB?
Of course, just like MS Access and other non-programmer programming platforms, it has some necessary limitations in order that the user won't get him or herself stuck... as John pointed out programming is hard. But it does give the user a lot of power, and it seems that most applications that non-programmers want to build are database-type applications anyway.