I am looking for some tool capable of creating complex process of data manipulation which can be more or less easily modified by people who do not write code.
For example, my task is:
fetch data from sourceA
2.1 if data is full - filter it by condition 45
2.2 if data is not full - fetch additional data from source B
if result passes validation - return 1, otherwise 0
This should be described in some readable manner, best option is if one can modify this process in some UI tool.
What are the requirements?
Each process consists of two parts: steps, and a way to arrange them in a sequence.
(1)
The process in each step should be able to
1. emit commands for fetching some data from data-sources and inserting this into process context
2. filter, enrich, transform datasets obtained
Thus each step of this process should be described with some more or less simple DSL.
(2)
The selection of the step to go, i.e. the consequence of steps should be described by some visual tool, or again, as in (1), with some simple dsl.
Can you advise something for this typical, from my point of view, task?
Meanwhile, here are my own ideas.
First think comes to mind is BPMN combined with Drools.
For steps I may use DRL rules: they can make only basic data manipulation themselves, but I can call Java functions from them if I need something complicated.
For steps consequence I may use standart BPMN diagramm.
Mat be, there is something better?
The combination of BPMN with DMN would allow you indeed to describe with these visual standards, the execution of the process and decision logic to be applied, in order to achieve what in the "For example" paragraph.
In order to make it fully accessible by the business people, the BPMN task for fetching the data or performing any interaction with external system, should be prepared in advance and made available during the composition of the BPMN/DMN diagrams.
Alternatively to BPMN+DMN combination, you can look into Fuse or Fuse Online, it cannot describe all the semantics of the BPMN+DMN combination, but with Fuse Online for instance you can fully visually implement the steps you described in the "For example" paragraph.
I am hoping that Combinator parsers, (http://debasishg.blogspot.com/2008/04/external-dsls-made-easy-with-scala.html), will work for a design to process the routing rules for a REST service that is implemented with Scalatra,(http://tutorialbin.com/tutorials/80408/infoq-scalatra-a-sinatra-like-web-framework-for-scala).
This REST service is to serve as a proxy so external applications can get access to services within the firewall, as it will have additional layers of security that can be customized for the business requirements of each REST service.
So, if a person wants to access their class schedule there will be less security than if you want to look at the transcript of someone.
I would like the rules for where to go to actually get the information, and how to return it, as well as what security is needed, in a DSL.
But, the first problem is how to dynamically change the routing rules for the REST service based on a DSL, as I am trying to create a framework that doesn't require a great deal of recompiling to add new rules, but just write the appropriate scripts and just let it be processed.
So, can a DSL be implemented using the Combinator Parser, in Scala, that will allow JAX-RS (http://download.oracle.com/javaee/6/tutorial/doc/giepu.html) to have dynamically changed routing?
UPDATE:
I haven't designed the language yet, but this is what I am trying to do:
route /transcript using action GET to
http://inside.com/transcript/{firstparam}/2011/{secondparam}
return json encrypt with public key from /mnt/publickey.txt
for /education_cost using action GET combine http://combine.com/SOAP/costeducate with
http://combine.com/education_benefit/2010 with
http://combine.com/education_benefit/2011 return html
These are two possible ideas where rules for a request for a transcript is sent to a different site, such as within a firewall, and the data is encrypted and returned.
The second would be more complicated in that the results of a SOAP and two REST requests will be combined, and there would need to be additional commands on how this is combined, but the idea is to put all of this in files that can be parsed on the fly.
If I used Groovy then some new classes could be generated for the routing, which would remove some performance hits, but I think using Scala would be the best bet, even if I took a performance hit.
My hope is to make a framework that is more maintainable so new routing rules can be written by people that don't know any OOP or functional languages, but the specifications could be written using Specs (http://code.google.com/p/specs/) so that the functional side could be certain that their requirements are tested on a regular basis.
UPDATE 2:
When I start working on a design I may intuitively understand some options, but not know why. Today I realized that the reason that Groovy may be a better fix for this is that I could then generate the classes for routing, using the metaprogramming (http://www.justinspradlin.com/programming/groovy-metaprogramming-adding-behavior-dynamically/), then I would be able to use Scala or Groovy to dynamically use the routing that was generated. I am not certain how to get Scala to generate the classes if they don't already exist.
In Groovy, as well as some other languages, as shown here (http://langexplr.blogspot.com/2008/02/handling-call-to-missing-method-in.html) if a method is missing you can dynamically generate the method and it will henceforth exist, so it will be missing one time.
It almost seems that I should be mixing Groovy with Java to make this work, but then the result may be that some of the code is in Scala and some in Java, for the routing of REST services.
Splitting the question in two parts:
can a DSL be implemented using the Combinator Parser
Yes. There are things that cannot be implemented using a combinator parser, or even other kinds of parser. For instance, Perl itself cannot be parsed (it must be evaluated). And combinator parsers are also not particularly good for complex languages (such as Scala -- its compiler is not based on combinator parsers), or if you demand top performance (such as the compilers used to compile hundreds of thousands of lines of code).
If, however, you plan to go to such extremes, choosing the parser is not going to be your main problem. For DSLs of average complexity, they'll do just fine.
that will allow JAX-RS to have dynamically changed routing
Well, I don't know JAX-RS, but if dynamically changed routing can be done with it, then combinators parsers will be able to provide whatever input is needed.
EDIT
Seeing your example, I think parser combinators are certainly enough. From their results, I expect you could dynamically create BlueEyes binders -- I haven't used BlueEyes, so I'm not sure how dynamic they are.
Another alternative would be go with Lift. Lift's binders are partial functions, and they can be combined in all the usual ways -- f1 orElse f2, f1 andThen f2, etc. I didn't suggest it at first because it is most often used with sessions, but it has a RESTful model which, I think, is stateless.
I don't know Scalatra, so I don't know if it would be adaptable to this or not.
The Pragmatic Programmer advocates the use of code generators.
Do you create code generators on your projects? If yes, what do you use them for?
In "Pragmatic Programmer" Hunt and Thomas distinguish between Passive and Active code generators.
Passive generators are run-once, after which you edit the result.
Active generators are run as often as desired, and you should never edit the result because it will be replaced.
IMO, the latter are much more valuable because they approach the DRY (don't-repeat-yourself) principle.
If the input information to your program can be split into two parts, the part that changes seldom (A) (like metadata or a DSL), and the part that is different each time the program is run (B)(the live input), you can write a generator program that takes only A as input, and writes out an ad-hoc program that only takes B as input.
(Another name for this is partial evaluation.)
The generator program is simpler because it only has to wade through input A, not A and B. Also, it does not have to be fast because it is not run often, and it doesn't have to care about memory leaks.
The ad-hoc program is faster because it's not having to wade through input that is almost always the same (A). It is simpler because it only has to make decisions about input B, not A and B.
It's a good idea for the generated ad-hoc program to be quite readable, so you can more easily find any errors in it. Once you get the errors removed from the generator, they are gone forever.
In one project I worked on, a team designed a complex database application with a design spec two inches thick and a lengthy implementation schedule, fraught with concerns about performance. By writing a code generator, two people did the job in three months, and the source code listings (in C) were about a half-inch thick, and the generated code was so fast as to not be an issue. The ad-hoc program was regenerated weekly, at trivial cost.
So active code generation, when you can use it, is a win-win. And, I think it's no accident that this is exactly what compilers do.
Code generators if used widely without correct argumentation make code less understandable and decrease maintainability (the same with dynamic SQL by the way). Personally I'm using it with some of ORM tools, because their usage here mostly obvious and sometimes for things like searcher-parser algorithms and grammatic analyzers which are not designed to be maintained "by hands" lately. Cheers.
In hardware design, it's fairly common practice to do this at several levels of the 'stack'. For instance, I wrote a code generator to emit Verilog for various widths, topologies, and structures of DMA engines and crossbar switches, because the constructs needed to express this parameterization weren't yet mature in the synthesis and simulation tool flows.
It's also routine to emit logical models all the way down to layout data for very regular things that can be expressed and generated algorithmically, like SRAM, cache, and register file structures.
I also spent a fair bit of time writing, essentially, a code generator that would take an XML description of all the registers on a System-on-Chip, and emit HTML (yes, yes, I know about XSLT, I just found emitting it programatically to be more time-effective), Verilog, SystemVerilog, C, Assembly etc. "views" of that data for different teams (front-end and back-end ASIC design, firmware, documentation, etc.) to use (and keep them consistent by virtue of this single XML "codebase"). Does that count?
People also like to write code generators for e.g. taking terse descriptions of very common things, like finite state machines, and mechanically outputting more verbose imperative language code to implement them efficiently (e.g. transition tables and traversal code).
We use code generators for generating data entity classes, database objects (like triggers, stored procs), service proxies etc. Anywhere you see lot of repititive code following a pattern and lot of manual work involved, code generators can help. But, you should not use it too much to the extend that maintainability is a pain. Some issues also arise if you want to regenerate them.
Tools like Visual Studio, Codesmith have their own templates for most of the common tasks and make this process easier. But, it is easy to roll out on your own.
It is often useful to create a code generator that generates code from a specification - usually one that has regular tabular rules. It reduces the chance of introducing an error via a typo or omission.
Yes ,
I developed my own code generator for AAA protocol Diameter (RFC 3588).
It could generate structures and Api's for diameter messages reading from an XML file that described diameter application's grammar.
That greatly reduced the time to develop complete diameter interface (such as SH/CX/RO etc.).
in my opinion a good programming language would not need code generators because introspection and runtime code generation would be part of language e.g. in python metaclasses and new module etc.
code generators usually generate more unmanageable code in long term usage.
however, if it is absolutely imperative to use a code generator (eclipse VE for swing development is what I use at times) then make sure you know what code is being generated. Believe me, you wouldn't want code in your application that you are not familiar with.
Writing own generator for project is not efficient. Instead, use a generator such as T4, CodeSmith and Zontroy.
T4 is more complex and you need to know a .Net programming language. You have to write your template line by line and you have to complete data relational operations on your own. You can use it over Visual Studio.
CodeSmith is an functional tool and there are plenty of templates ready to use. It is based on T4 and writing your own temlate takes too much time as it is in T4. There is a trial and a commercial version.
Zontroy is a new tool with a user friendly user interface. It has its own template language and is easy to learn. There is an online template market and it is developing. Even you can deliver templates and sell them online over market.
It has a free and a commercial version. Even the free version is enough to complete a medium-scale project.
there might be a lot of code generators out there , however I always create my own to make the code more understandable and suit the frameworks and guidelines we are using
We use a generator for all new code to help ensure that coding standards are followed.
We recently replaced our in-house C++ generator with CodeSmith. We still have to create the templates for the tool, but it seems ideal to not have to maintain the tool ourselves.
My most recent need for a generator was a project that read data from hardware and ultimately posted it to a 'dashboard' UI. In-between were models, properties, presenters, events, interfaces, flags, etc. for several data points. I worked up the framework for a couple data points until I was satisfied that I could live with the design. Then, with the help of some carefully placed comments, I put the "generation" in a visual studio macro, tweaked and cleaned the macro, added the datapoints to a function in the macro to call the generation - and saved several tedious hours (days?) in the end.
Don't underestimate the power of macros :)
I am also now trying to get my head around CodeRush customization capabilities to help me with some more local generation requirements. There is powerful stuff in there if you need on-the-fly decision making when generating a code block.
I have my own code generator that I run against SQL tables. It generates the SQL procedures to access the data, the data access layer and the business logic. It has done wonders in standardising my code and naming conventions. Because it expects certain fields in the database tables (such as an id column and updated datetime column) it has also helped standardise my data design.
How many are you looking for? I've created two major ones and numerous minor ones. The first of the major ones allowed me to generate programs 1500 line programs (give or take) that had a strong family resemblance but were attuned to the different tables in a database - and to do that fast, and reliably.
The downside of a code generator is that if there's a bug in the code generated (because the template contains a bug), then there's a lot of fixing to do.
However, for languages or systems where there is a lot of near-repetitious coding to be done, a good (enough) code generator is a boon (and more of a boon than a 'doggle').
In embedded systems, sometimes you need a big block of binary data in the flash. For example, I have one that takes a text file containing bitmap font glyphs and turns it into a .cc/.h file pair declaring interesting constants (such as first character, last character, character width and height) and then the actual data as a large static const uint8_t[].
Trying to do such a thing in C++ itself, so the font data would auto-generate on compilation without a first pass, would be a pain and most likely illegible. Writing a .o file by hand is out of the question. So is breaking out graph paper, hand encoding to binary, and typing all that in.
IMHO, this kind of thing is what code generators are for. Never forget that the computer works for you, not the other way around.
BTW, if you use a generator, always always always include some lines such as this at both the start and end of each generated file:
// This code was automatically generated from Font_foo.txt. DO NOT EDIT THIS FILE.
// If there's a bug, fix the font text file or the generator program, not this file.
Yes I've had to maintain a few. CORBA or some other object communication style of interface is probably the general thing that I think of first. You have object definitions that are provided to you by the interface you are going to talk over but you still have to build those objects up in code. Building and running a code generator is a fairly routine way of doing that. This can become a fairly lengthy compile just to support some legacy communication channel, and since there is a large tendency to put wrappers around CORBA to make it simpler, well things just get worse.
In general if you have a large amount of structures, or just rapidly changing structures that you need to use, but you can't handle the performance hit of building objects through metadata, then your into writing a code generator.
I can't think of any projects where we needed to create our own code generators from scratch but there are several where we used preexisting generators. (I have used both Antlr and the Eclipse Modeling Framework for building parsers and models in java for enterprise software.) The beauty of using a code generator that someone else has written is that the authors tend to be experts in that area and have solved problems that I didn't even know existed yet. This saves me time and frustration.
So even though I might be able to write code that solves the problem at hand, I can generate the code a lot faster and there is a good chance that it will be less buggy than anything I write.
If you're not going to write the code, are you going to be comfortable with someone else's generated code?
Is it cheaper in both time and $$$ in the long run to write your own code or code generator?
I wrote a code generator that would build 100's of classes (java) that would output XML data from database in a DTD or schema compliant manner. The code generation was generally a one time thing and the code would then be smartened up with various business rules etc. The output was for a rather pedantic bank.
Code generators are work-around for programming language limitations. I personally prefer reflection instead of code generators but I agree that code generators are more flexible and resulting code obviously faster during runtime. I hope, future versions of C# will include some kind of DSL environment.
The only code generators that I use are webservice parsers. I personally stay away from code generators because of the maintenance problems for new employees or a separate team after hand off.
I write my own code generators, mainly in T-SQL, which are called during the build process.
Based on meta-model data, they generate triggers, logging, C# const declarations, INSERT/UPDATE statements, data model information to check whether the app is running on the expected database schema.
I still need to write a forms generator for increased productivity, more specs and less coding ;)
I've created a few code generators. I had a passive code generator for SQL Stored procedures which used templates. This generated generated 90% of our stored procedures.
Since we made the switch to Entity Framework I've created an active codegenerator using T4 (Text Template Transformation Toolkit) inside visual studio. I've used it to create basic repository partial classes for our entities. Works very nicely and saves a bunch of coding. I also use T4 for decorating the entity classes with certain Attributes.
I use code generation features provided by EMF - Eclipse Modeling Framework.
Code generators are really useful in many cases, especially when mapping from one format to another. I've done code generators for IDL to C++, database tables to OO types, and marshalling code just to name a few.
I think the point the authors are trying to make is that if you're a developer you should be able to make the computer work for you. Generating code is just one obvious task to automate.
I once worked with a guy who insisted that he would do our IDL to C++ mapping manually. In the beginning of the project he was able to keep up, because the rest of us were trying to figure out what to do, but eventually he became a bottleneck. I did a code generator in Perl and then we could pretty much do his "work" in a few minutes.
See our "universal" code generator based on program transformations.
I'm the architect and a key implementer.
It is worth noting that a significant fraction of this generator, is generated using this generator.
We uses Telosys code generator in our projects : http://www.telosys.org/
We have created it to reduce the development duration in recurrent tasks like CRUD screens, documentation, etc...
For us the most important thing is to be able to customize the generator's templates, in order to create new generation targets if necessary and to customize existing templates. That's why we have also created a template editor (for Velocity .vm files).
It works fine for Java/Spring/AngularJS code generator and can be adapt for other targets (PHP, C#, Python, etc )