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I would like some practical guidance on when I should use a Domain Specific Language. I have found resources about advantages and disadvantages, but what kind of project would warrant its use?
It seems like there is a big investment in time to create and maintain a DSL, so in what application space would I get a productivity return on my time investment?
Edit: It seems the most common use of DSL is for file formats for persisting data state, what about using a DSL for program logic and structure(perhaps code generation)? When is this feasible?
Edit #2 I am mainly asking about when is creating a specific DSL worthwhile. Of course we should use existing DSLs as much as possible to save time.
There are very few good reasons for creating yet another DSL. The world is fat with special-purpose languages.
Think along with these lines.
Solve the problem with a general-purpose language such as Python, Java, C++.. whatever.
Optimize that solution to factor out the common features and build a really nice, really elegant, really extensible class library.
Optimize that class library to emphasize "orthogonality". Make sure all features work well together, without any problems.
If you need simplification of the syntax only, create a scripting wrapper around your nice class library. This is your DSL. For Python, this is easy -- it's already a dynamic language. For Java, there are things you can leverage. For C++ it can be a bit of work to build this flexible scripting environment.
If you still need further optimization, consider writing a compiler for your DSL.
The ACM Computing Surveys article When and How to Develop Domain-Specific Languages provides advice on just this topic, as does Martin Fowler's 2010 book Domain-Specific Languages.
Firstly, I would use a DSL when the problem domain your developing against is a widely well known domain, and some business experts of that domain have already went through great lengths to build such a DSL so that you wouldn't have to go through the lengths yourself to solve all the problems they have already figured out.
If you're thinking of creating a DSL, I would consider doing so if your business is done in a very particular area, and you spend the majority of your time focusing in a specific problem domain. If you bounce around doing applications for multiple problem domains, then I wouldn't advise taking that approach.
For example, if your business is soley in building tax applications, it might be a good idea to build a tax system DSL. This would allow your language not only to be useable by you in your various tax applications, but it would also be marketeable (useable) by other businesses in your industry that want to do similar things that you're accomplishing.
Of course, you have to weight the costs/benefits of building a DSL vs a framework on top of an already existing language.
One situation that comes to mind is when the requirements requires a very high or improbable level of customization/configuration. So you would provide a kind of scripting model against a DSL instead.
Takes a car assembly "arm" for example, providing a configuration model to support various factory configurations would be impossible. (detect this, don't detect that, when this happens do this ... etc.)
But compiling a new application with specialized logic for each customer is probably not a good way to go. So in this case, you create a little framework that would becomes a kind of DSL, and then for each robotic arm you sells, you write a little app in your DSL and save it along with the core software that would compiles and runs your DSL scripts instead. Or better yet, tools to program the DSL are included along with the robotic arm so your customer can "program" the arm themselves in the DSL you created.
One real world examples that comes to mind is Yahoo Pipes (you could think of it as a DSL) or the robots.txt directive for automated web crawler for example. They may not be a full-blown DSL but they demonstrate where DSL might be useful.
Well, someone has to say it, so here goes:
Lisp is regarded by some as the domain specific language for any domain. A well-supported and very extensible DSL at that.
In some cases, fashioning a DSL from Lisp (or a similar language such as Haskell) could actually provide a lot of power with minimal effort, and thus would be quite worthwhile. DSLs do not always need to be big maintenance burdens.
The most obvious is you should definitely use them when the language already exists and is well-supported. The prime examples of this are UIL for Motif-based GUI development and make for software builds.
If you have to make your own, I'd say to look for domains a large amount of effort is in just specifying things properly, and where your compiler can't really find most errors, but a domain-specific compiler could. GUIs are a great example, as most of the work is in setting up the layout, and there are generally lots of ways to make syntacticly valid C++ calls that make no sense whatsoever to your underlying GUI system (EG: trying to embed an entire dialog widget inside a button).
I find UIL particularly a huge gain for GUI development because a UIL compiler can find errors in a GUI specification that just look like nice normal compilable code to a C++ compilter. The fact that it is well-supported means that the code is easy to port between platforms, and even GUI builders.
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So, I've got an idea for a website. I can start off using any platform and frameworks I want, but there are almost too many options.
OS Platform:
Windows, *nix
Web Framework:
Rails, ASP.NET, ASP.NET MVC, Django, Zend, Cake, others
Hosting:
EC2, Dedicated Server, Shared Hosting, VPS, App Engine, Azure, others
Persistence:
S3, MySql, PostreSql, Sql Server, SimpleDB, CouchDB, others
How do you avoid decision paralysis and get started?
Firstly, your familiarity with a framework's language should dictate which framework you choose. Don't add the burden of learning another language on top of learning a framework.
Next, have a look at the remaining frameworks. Do they have good documentation? What about the community. (A good community can go a long way to making up any shortcomings of a given technology.) Does the framework solve the problems that you need solved?
Finally, just dive in and try something! Pick the one that makes the most sense to you and start writing code. Don't do too much hand-wringing over your decision. If it becomes obvious that you made the wrong choice, it should be obvious quite early. Learn from what you've accomplished so far and consider restarting with a different technology. (Just don't get several weeks down the road before you make this decision!)
I'm sure you don't like all of those technologies equally. Pick a framework that you like and get to work.
It depends on what your app is going to be doing. A handful of the technologies you listed are direct competitors (like Django vs. Rails), but some are completely different ways to do things (like MySQL vs. S3).
Questions to answer before you begin:
Will the app need to be horizontally partitioned in the near term? If so, using EC2, Google App Engine or Azure would be a good option.
Will your app fit into the constraints of Google App Engine? If so, it requires a lot less hassle on your part than running on bare metal (whether real or virtual).
What's your preferred web framework? If you want an MS framework, you'll need to run on a host that supports that.
What will your persistence and data access patterns look like? This will determine whether to use a database or something more exotic.
If you are running on EC2, the other AWS services are more appealing. Similarly, if you are using GAE, you have only one option for persistence. If you are using Rails, may as well start with MySQL.
In answer to your question of how to reduce the number of options, the answer is to realize that many of the options are related, so you don't have as many choices to make as it first appears.
Some advice that was once given to me is, pick what your friends (or colleagues) are using. Having people around you that you can share ideas and the learning experience with is invaluable.
If you want to learn something new: I'd just go with your gut and get started. If it sucks then switch to something more familiar.
If you don't have much time: Go with what you know and forget about the other options. Just start coding.
Optimize for happiness. Pick the one that you like the most. Or the one that intrigues you the most.
I've worked in Microsoft shops, in Ruby on Rails, and in homegrown shops having Apache, Jetty, even Mason.
All frameworks have their warts, their idiosyncracies that will keep you up until 3 AM, and their "tribal knowledge" vagaries that will be completely unexportable to other frameworks. (The last point is sometimes by design, the whole "platform entrenchment" business strategy)
Listen to what the supporters of the frameworks say about the problems with the other frameworks (Google: X framework vs Y framework). Pick the framework that has the loudest supporters. If they are equally loud, make the decision with a dice roll.
With me it's simple.
I only know MS stack and see no point in "checking out" all of those you mentioned.
No, actually I once tried to use JSF before excluding it from my list permanently.
Use what you are experienced in and where you can be more productive. The objective is to get your site up and running. Go for it.
One of the biggest factors in determining which platform/framework to use is your budget. You have to factor in the cost of licensing, software required to develop/maintain your website and other miscellaneous costs.
I suggest you begin with a scorecard of your own construction. Perhaps you can find different ones on the web, but if you do, modify them to meet YOUR needs. There should be a scorecard for each level in the stack (as you've described). Each scorecard should share some aspects to grade with other scorecards but each will also have their unique aspects.
Once constructed, weight each aspect graded according to your needs.
Once you've chosen the weights, pick the scales for grades.
At this point promise yourself you wont mess with the weights or the scale and then start collecting data on your options for each level in the stack.
You may also want to put a time limit on the collection period.
Make your decision based on the outcome of the scorecard.
The beauty of this approach is that the effort is made in constructing the scorecard, not in circular arguments of options. The effort in making the scorecard is vendor agnostic and focuses on the desired result, not the options. Thus you can avoid paralysis.
One more thing, my best scorecards have included sections addressing the availability of resources and other human related things. Don't make the mistake of just looking at the technology.
good luck.
Go for personal preferences.
One decision at a time:
Firts I would begin with type of language:
Script: PHP, Python,
Serious: Java, .Net
The language will restrict your OS, plattform and will give you hints for the dataabse decission. The database load is also important. And, Do you want logic in the DDBB? how much data?
Last advice. Try combinations well tested. LAMP, WAMP, Windows with SQL Server and .NET.
Evaluate each platform and technology for quality of tools for your needs. For example, if you are cost sensitive, you would value free operating systems and tools higher than costly ones. If you need performance, you would value tools which provide high performance higher than ones that don't.
It entirely depends on your situation. I spent several months evaluating stuff for a new commercial web site last year, and it was very easy to feel paralized. In the end it was talking to several people who'd done similar things, and of course reading a lot of stuff online and from Amazon. I chose Java, since our team had a lot of experience in it, and it has good performance and extensive supporting technologies. Oracle is our database but we used a persistence manager to make it easy to change later on. We used a half-dozen very good libraries to eliminate much of the boring and repetitive coding (Restlet, iBatis, Freemarker, XStream, jQuery, SLF4J). We used Glassfish as our web server.
Yours sounds like a small project with only you to work on it. In that case, pick a complete framework instead of a smorgasbord like we did. Pick something fun to work with, and something with good "return on resume". Look very hard at Ruby on Rails, Django (kind of a Python on Rails), and Groovy on Grails (a Rails-wannabe for the Java world). In your shoes I'd pick Ruby on Rails because there's a large and growing community and a good number of books and tutorials. Plus, Ruby looks like a worthwhile language to learn. For your database, just pick one. These frameworks make it easy to change your mind later. Pick MySQL unless you have another you like better.
And as other posters said, just do it! ;-)
Like others said, pick something you and your employees are familiar with. I highly doubt you are close to being industry ready with all those techs.
OS Platform: Windows, *nix
Shouldn't matter except for Windows licensing costs, and that is probably the least of your expenses.
Web Framework: Rails, ASP.NET, ASP.NET MVC, Django, Zend, Cake, others
Dependent on your favorite language
Hosting: EC2, Dedicated Server, Shared Hosting, VPS, App Engine, Azure, others
You should design your product to be movable, so you can scale among these. If you know for sure you are going big, then just start off with EC2. App Engine is extremely limiting, ex. they don't let you form outbound connections.
Persistence: S3, MySql, PostreSql, Sql Server, SimpleDB, CouchDB, others
You need to do the research yourself whether or not your product requires an RDBMS or a simple key/value store, and what features each of these have.
Just go for it! Your platform choice really is not all that important as long as you make a reasonable choice (Ruby + Rails, Python + Django, PHP + Cake/CodeIgniter). Any of these can be used to build successful sites. If your site really takes off, you'll be able to scale it fine.
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I'm facing developing a new web app in the future and I'm wondering how to decide what framework to use. I've settled on Python as my language of choice. But there are still may frameworks to choose from! More generally how do you choose between different similar technologies that are still in the works as the latest round of web frameworks are? I'm curious what your process is for deciding on technologies you've never used.
Recognize that no choice is perfect -- or even very good.
No matter what you choose, someone will have a suggestion that -- they claim -- is better.
No matter what you choose, some part of your tech. stack will fail to live up to your expectations.
The most important thing is "shared nothing" so that the components can be replaced.
After that, the next most important thing is automatically-generated features to reduce or prevent programming.
Look at Django. Lots of automatic admin features make life very pleasant.
There are a number of things you can do:
Download the frameworks and build something similar with them for comparison.
Look for comparisons by other people, but attempt to understand the bias of the reviewer.
Observe the community at work, see what people are building and the issues they run into when using the technology. Forums, blogs, mailing list etc are good places to check out.
Go to conferences and meet like minded developers interested.
You can also take the approach of using stable versions rather than alpha bits. After a while you might move closer the bleeding edge. People associated with the project in question are generally more biased than those approaching from other platforms, be careful who you trust.
Consider the impact of using a bleeding edge framework versus an established one. Sometimes it's important to your customers that you are on one perceived as stable. At other times this doesn't matter. How comfortable are you with fixing the framework itself? Great developers will learn the internals, or at least know enough to keep things moving whilst a bug is sent to the framework mailing list etc.
Consider some general best practices in building abstractions and reusable code on the python platform. You may be able to save yourself some work in moving to another platform. However, don't be a reuse junkie as this can limit the effectiveness of your use of the framework. The 37Signals guys are right when they talk about extracting frameworks from working code rather than building frameworks from scratch.
I know this is an old posting, but I am in a similar situation (again) and I think there are other people who may want to look for different opinions, and hear of (somewhat) successful experiences.
Since baudtack mentioned Python, I will try to answer this along the lines of my experiences using Python. Here is what has been working for me:
determine the scope of your project - outlining what your application is supposed to be able to do without introducing any programming or design notes will clarify your goals greatly
determine how you would like to work with your code, stack and data:
a. what sort of programming paradigm do you want to work with? i.e. object-oriented, functional, etc. do you want to play to your programming style or do you want to follow somebody else's programming style?
b. use semantic web or not? do you want greater control over URIs and their design? (I found web.py great for this by the way - It is my choice to create REST APIs in Python)
c. do you want to be trapped by framework requirements, or do you want a better separation of the application from the web component, i.e. use a framework to utilize your application as a set of modules, for example. My problem with Django was that I ended up not programming Python, but having to learn more Django than I needed to. If that works for you, then that is the way to go.
d. data stores... some sort of SQL vs. non RDBMS (xml databases like eXist-db with full xquery support) vs. OODBMS vs. a combination of the above? how complicated do you need this to be? how much control/separation do you need to have over how data gets stored and recalled in your application?
e. testing: unit tests... thank goodness for python! if your web app has the potential to grow (as they often do), having a sane and coherent testing platform to begin with will help out a lot in the future - I wish I had learned about this earlier on. oh well... better late than never.
f. how much control over the server do you need? hosting considerations? how much control over an Apache instance do you need to have? OS specific needs? I found that using shared hosting providers like Webfaction has been great. I eventually found I needed greater needs for flexibility and bandwidth. In other words, what can you get for your budget? If you have USD50 to spend each month, it may be better to consider a virtual hosting solution like Linode....
Finally, I echo S.Lott's sentiments that no choice for a solution is perfect, and are subject to obsolescence.
Experience trumps hearsay. I've found that prototyping is a huge help. Make a prototype that uses the features you expect to be the most important for various frameworks. This helps route out any features that may not work "as advertised."
In general though, kudos for being willing to look at new technologies.
I have a set of criteria in different categories:
Activity & Documentation
Is there an active user base?
Is there an active development base?
Is the support responsive and information accessible?
Are there user and development guides and reference material?
These are essential, there needs to be traceability of all of these to build confidence in the solution.
Ease of use
Are basic features easy and complex features possible? I typically give a new framework a test drive and try to roll out a set of use cases to see how intuitive the framework is to use.
Is installation intuitive and simple for a local/dev installation and production deployment?
How is it backed up and upgraded?
What is the effort and UX for implementing a "Hello World" type blog post, static page, menu item, and plugin?
How are versions dealt with for the core & plugins?
Example (on the topic of Automated Testing/Continuous Integration solutions)
Several years ago I evaluated several Automated Testing solution. At the time Jenkins and TeamCity were front runners and in the end I chose TeamCity because of the UX, active user & development base and quality of accessible documentation.
Example (CMS for a blog)
This criteria is also why I prefer to use Wordpress over other options. While wordpress has its shortcomings, the user and development base is strong and active which leads to a software architecture with more potential to evolve over time and maintain its relevance and a development community that provides quality plugins and themes to choose from.