I've been working with yocto for a while. The job involves adding a layer on top of meta-yogurt, and thus adding new or modifying existing recipes in this layer. It has been working out so far.
But through struggling with recipes/rules syntax and relationships between them, my gut told me that it would be much easier for the internal implementation of the build system, as well as how the build system interacts with end-developer like me if a relational database had been involved, which defines things, their attributes and their relationships.
But I am no yocto expert (and cannot spend time on it, considering my project schedule) to evaluate a re-design of yocto with a relational DB. Just wonder if this also makes sense to anybody?
Speaking as one of the developers who's worked extensively on bitbake whilst I can see why you might think this, it doesn't really make sense for many reasons, not least performance. We once did try using sqlite as a data store backend within bitbake and it was orders of magnitude too slow to be useful compared to our python data store.
The flexibility in the metadata also comes from things like the ability to inject python code and with a database engine, this wouldn't be easily possible.
So in summary, I doubt bitbake or the Yocto Project will ever use relational databases in this way.
I tried to post a comment to Richard Purdie answer from Oct 7 '17 but the comment box didn't allow line break and long text...
I was not aware that there was already a python data store besides yocto objects and rules (mixture of variables, string literals, reg.exp., file types eg. layer, bb, bbappend, conf, inc etc and the "half-explicit", "half-documented" syntax and relationship among them :().
Of course in python environment, it makes most sense to use the combination of its data store and language binding and not another relational db. But I imagine with a relational db, every things such as data store and rules can be implemented in one place, querying/modifying is also an integrated part, binding to different languages / scripting should be possible. Was it actually the same, just the "python way" that I am not familiar with?
When it goes to performance, we already needed a powerful machine (Xeon E5 16G DRAM 1T HDD) to clean build one distro (without fetching sources from remote servers) in an hour and believe other people also use their best available PC for such a serious job as building a distro. So without comparing performance of different db engines and programming languages, which can't be different in great magnitude, I would just forget the performance factor.
Injecting code into a database engine might be difficult. But I guess when using a database engine, just a different programming pattern does the job: the logic of the job is implemented outside the db engine and this process contacts the db engine when needed.
I've been actually not working with yocto for awhile because our yocto build setup actually has been working great and producing new distros for us now and then with the previously prepared layer. Just some thoughts ...
Related
With the rising of non-sql database usage in high traffic website, I'm interested to use it for my project. Now I've heard several names like Voldermort, MongoDB and CouchDB. But which are among these NonSQL database that is production ready? I've seen the download pages and it seems that none of them is production ready because is not version 1.0 yet. Is there any other names other than these 3 that is recommendable to be used in production?
What do you mean by production ready? As far as I know, all of them are being used on live systems.
You should make your choice based on how the features they provide fit your needs.
You can also add Tokyo Cabinet to the list as well as the mnesia database provided by the Erlang VM.
I think you need to start out from your project requirements to see what kind of database you really need. There are many non-relational DBMS:s out there and they differ a lot in what kind of problems they are good at solving. I think the article Should you go Beyond Relational Databases? by Martin Kleppmann is a good starting point for finding out what you need. There's also a lot of stackoverflow threads on similar topics, these are my favorites:
The Next-gen Databases
Non-Relational Database Design
When shouldn’t you use a relational
database?
Good reasons NOT to use a relational
database?
When you have narrowed down what you actually need you can take a deeper look into the alternatives to see which DBMS are production ready for your use case. Production readiness isn't a yes/no thing: people may successfully deploy some solution that for example lacks in tool support - in another project this could be a no-go.
As for version numbers different projects have a different take on this, so you can't just compare the version numbers. I'm involved in the graph database project Neo4j and even if it has been in production use for 5+ years by now we still haven't released a version 1.0 final yet.
I'm tempted to answer "use SIRA_PRISE".
It's definitely non-SQL.
And its current version is 1.2, meaning that someone like you must definitely assume it's "production-ready".
But perhaps I shouldn't be answering at all.
Nice article comparing rdbms with 'next gen' and listing some providers:
Is the Relational Database Doomed?
http://readwrite.com/2009/02/12/is-the-relational-database-doomed
I will suggest you to use Arangodb.
ArangoDB is a multi-model mostly-memory database with a flexible data model for documents and graphs. It is designed as a “general purpose database”, offering all the features you typically need for modern web applications.
ArangoDB is supposed to grow with the application—the project may start as a simple single-server prototype, nothing you couldn’t do with a relational database equally well. After some time, some geo-location features are needed and a shopping cart requires transactions. ArangoDB’s graph data model is useful for the recommendation system. The smartphone app needs a lean API to the back-end—this is where Foxx, ArangoDB’s integrated Javascript application framework, comes into play.
Another unique feature is ArangoDB’s query language AQL — it makes querying powerful and convenient. AQL enables you to describe complex filter conditions and joins in a readable format, much in the same way as SQL.
You can model your data in several ways:
in key/value pairs
as collections of documents
as graphs with nodes, edges, and properties for both
You can access data in ArangoDB:
using the general HTTP REST API via curl/wget, or your browser
via the ArangoDB shell (“arangosh”)
using a programming language specific client library
Server requirements for ArangoDB:
ArangoDB runs on Linux, OS X and Microsoft Windows.
It runs on 32bit and 64bit systems, though using a 32bit system will limit you to using only approximately 2 to 3 GB of data with ArangoDB.
I was thinking of starting a project that very clearly needs a persistent store. I was about to reluctantly decide on a RDBMS, when I came across an article which briefly mentions CouchDB. Seems some advancements in DB technology have happened since I last looked, so I thought I would ask here about databases before I got into it.
Here are my criteria. ( I list the criteria again at the end, so if you want to skip the explanations just scroll down. )
The project is open source and I will not be asking anything for it, so preferably the database is open source and free. Furthermore the software has to run on both Linux and Windows.
There are parts of the project that have to be in C++. The project is not large enough code wise to justify using a second language. So basically the whole thing will be C++.
This project will not have anything to do with the web, so preferably
the database will not require the detritus of a web library.
The objects I want to store fall into one of two categories: a basic object and a container object. The difference being objects which are containers will contain even more objects, ie: a parts of parts problem. I need a database that can handle such cases cleanly and efficiently.
I also expect the schema to evolve rapidly, at least initially. I alse suspect that some of the old data simply will not fit into the new schemas. So I would like to keep different versions of the schema around. Win possible, I would like to be able to transform data in one to schema into another schema.
For the application to work the way intended, people would have to exchange large chunks of database with each other. So I would want simple ways of importing and exporting data, which I could automate to some degree.
Finally it would be nice if the database could in someway be simulated in unit tests.
THose are my requirements. I have replicated them below to make it easier for people answering.
Thank you
Non Technical requirements
1. Open source preferably free.
2. Run on Windows and Linux
Has a C++ interface.
Is able to handle a non-web application, preferably without REST.
Can handle a "parts of parts" problem fairly well.
Can handle multiple indexes.
Has sort of concept of schema version, can handle multiple schema versions, and can migrate tables from one schema to another.
Should have a simple mechanism for move data from one instance of the database to another.
Preferably has some mechanism for testing.
HDF5 is a binary format which behaves like an hierarchical database. It has binding and libraries for C++ and python (I only use the latter) and it is used to store big amounts of data, like the ones produces in certain physics and astronomy experiments.
http://www.hdfgroup.org/HDF5/
I've looked at a few nosql databases some time ago (had an different requirement than than you though - needed it to be a standalone server). The ones that I remember as particularly interesting are Redis and Kyoto Cabinets. Have a look.
BTW, you don't mention any performance requirement. If so, have you considered SQLite? Simple, embedded, stable, and with the flexibility of SQL after all. With prepared statement the performance penalty of SQL should not be very high.
EDIT: ooops, just noticed that you asked this more than a year ago... Well, perhaps you can tell us what you've chosen :)
I know this is not a programming question per se, but I wanted to get as much input from the SO community on a new project I hope to get started. The project is from being started from scratch and thus every decision for programming languages, databases, frameworks, platforms and what not are up in the air. I'm hoping to get your opinion on the matter, what you feel are the strengths and weaknesses of each option.
Database:
Currently I have the option of using MSSQL or MySQL. While I am leaning towards using MySQL because it is free and most probably has all the features I need. However, there is the possibility of having a lot of hierarchical data and the new hierarchical data type in MSSQL is quite appealing. Does it really simplify matters that much? Also MSSQL supports many more advanced SQL functions that may or may not be useful in the long run. While for development I can get access to Server 2008, multiple licenses as the development team grows and for production, are the costs justified?
Programming Languages:
The project will have a web based front end UI and a server based component that will do some heavy lifting.
For the web based UI, I was thinking of maybe doing Apache/IIS with PHP or IIS with ASP.Net in C#. I'd like to use a good framework to properly utilize good design patterns that should structure the code and development of the app. As well as make modifications in the long run easy to implement. I also want the GUI to look good and don't like the idea of buying .Net controls from component vendors. Instead I prefer the idea of using good CSS, and open sources like YUI and javascript to make the UI sleek.
For the server based component, I was thinking of using C#. I have no real development experience in C++ and I'd like good libraries and sufficient speed is good enough. However, while the web based UI and server based component is loosely coupled, there may be instances where the UI needs to communicate (call methods and what not) with the server based component and I want to pick languages/frameworks that will play nice with each other.
All suggestions on frameworks to incorporate are welcome.
Version Control:
I have had good experiences with SVN and a pretty bad experiences with TFS. I've never worked with GIT. Which do you think is better in terms of features as well as general developer familiarity. I want to pick something that other developers will know and not have trouble with.
I apologize if the questions are bit redundant or I'm not providing enough information or using bad terminology. I plan to edit and improve the question as I get feedback. Thanks!
EDIT:
Who: This would most probably be a startup formed of college students or junior developers. I want the project to utilize technologies that most people are familiar with or are easy to pick up.
What: I'd need hours and days to explain the solution. But in the end when you break it down, its a web based UI (think standard web app to just manage database data) that would be used to knowledgeable clients. The server based component would be very separate except for the fact that it should be able to communicate with the web app.
I can provide more information as required but I would appreciate an opportunity for users to answer and provide their ideas before you hastily close the question.
Obviously it depends a lot on specific requirements, but then again, even with those I probably wouldn't be able to tell for sure!
I've been working on a from-scratch project myself for a couple of months, and have generally found:
Choosing Microsoft for all the layers just goes down much easier (my subjective opinion). For example I would use C# for the UI, the back end, and use MSSQL for the database. Nothing at all wrong with non-Microsoft vendors, I'm no Microsoft fan-boy, I just struggle to get productive with unfamiliar tools. Depends where your experience lies though.
Database: In particular I've found that .NET and MSSQL go easily together. When I started the project I was using a PostgreSQL (because it's free, fully featured and has open-source warm fuzzies). However I abandoned it in favour of MSSQL simply because it was taking me too long to get database work done in an unfamiliar language with unfamiliar tools. Also, I'm not sure MSSQL is so expensive anymore, for example for a web application, MSSQL 2008 Web Edition is pretty damn cheap per-processor I think (only on SPLA licensing though). If you're concerned about database features in a free implementation though, personally I think PostgreSQL has a very full feature set, nicely standardised, and rapidly growing.
UI: I'm pretty inexperienced, but ASP.NET MVC looks far less painful to me than ASP.NET Web Forms. I like PHP too, but again I'd match the UI language with the back-end language, so would recommend .NET.
On frameworks, I'm immersed in DALs at the moment. I like Subsonic for lightweight data, NHibernate for heavy-weight.
I still have a long way to go with my project so perhaps I can only see the short-term benefits and drawbacks at the moment. But in general I would say: use the technologies that you're most comfortable using, as you'll be way more productive and the end result will probably be about the same anyway. If you want to learn new technologies though, and who doesn't? - go ahead, just expect it to take a lot longer.
Didn't want to answer 'cause it's so open ended. But a few points:
Money
First, check out BizSpark. That should take care of any money aspect for 3 years. For a service company, that means not only free VS Team Suite and Office and so on, but free Windows, SQL, etc. If your startup can't afford to spend a bit on MS tech in 3 years, it's probably a bad business. So that takes out licensing.
On a similar note, Sun has Startup Essentials. Could be interesting on the hardware side of things, but I haven't actually competitively priced them versus Dell/HP.
Software
It doesn't sound like you have hard enough requirements to say "oh, this slightly-less-popular software X is perfect for my domain Y and is gonna give me a very big boost". In fact, your project might not be like that at all. Maybe it, technically, is going to be a relatively plain application just pushing data around or whatever. You didn't specify.
For a small startup, personal productivity is probably going to trump any other argument. If your people are excellent in X, then that's one of your top arguments right there.
If you really don't have any particular system you're most comfortable with, be conservative. Stick with .NET or Java, as they'll give you the widest range of useful possibilities.
As far as things like OS and Database, I'm biased, but I think Microsoft will give you platforms that are easier to take advantage of than you'll find elsewhere. For instance, setting up load balancing, clustering, centralized authentication, managing servers (updates, events, etc.) is going to be easier to get going on Windows than it would be on another platform, assuming you're not an expert in either. Configuring SQL Server, even the advanced features, is a piece of cake. (Go time someone who knows neither: Setup a DB mirror in MSSQL and MySQL -- which is going to take more work?) Again, this is all predicated on you not having experts in a particular set of technology.
Don't mix -- whatever you do, stick with the platform. If you go .NET, MSSQL is going to work better with the data providers (or things like Linq-to-SQL). If you decide to do PHP, then use MySQL as everyone else uses it and you'll encounter less resistance. If you're not inventing stuff on the technical side, don't become an edge case.
You should pick the platform first, then the language that is best for that platform (if there is any choice).
One thing you should consider is the labor pool, and labor pool cost, for specific platforms and languages. Human Resources can often get cost metrics, if you don't have ideas already.
In my town, for example, .NET platform is much more expensive per Software Engineer than open source, because the .NET developers have a higher rate (40% roughly). C# is a little higher rate than VB.NET, but also tends to bring more well rounded candidates.
Just to throw in something totally different: How about weblocks as a web framework? It uses Hunchentoot as a server, which can run either standalone or with Apache. This is all done in Common Lisp. Weblocks can use cl-sql as a backend store, which can connect to many different RDBMs (MySQL, PostgreSQL, Oracle, ODBC, SQLite).
When dealing with small projects, what do you feel is the break even point for storing data in simple text files, hash tables, etc., versus using a real database? For small projects with simple data management requirements, a real database is unnecessary complexity and violates YAGNI. However, at some point the complexity of a database is obviously worth it. What are some signs that your problem is too complex for simple ad-hoc techniques and needs a real database?
Note: To people used to enterprise environments, this will probably sound like a weird question. However, my problem domain is bioinformatics. Most of my programming is prototypes, not production code. I'm primarily a domain expert and secondarily a programmer. Most of my code is algorithm-centric, not data management-centric. The purpose of this question is largely for me to figure out how much work I might save in the long run if I learn to use proper databases in my code instead of the more ad-hoc techniques I typically use.
1) Concurrency. Do you have multiple people accessing the same dataset? Then it's going to get pretty involved to broker all of the different readers and writers in a scalable fashion if you roll your own system.
2) Formatting and relationships: Is your data something that doesn't fit neatly into a table structure? Long nucleotide sequences and stuff like that? That's not really conveniently tabular data.
Another example: Nobody would consider implementing software like Photoshop to store PSDs in a relational format, because the data structures don't really lend themselves to that type of storage or query pattern.
3) ACID (sort of a corollary to #1): If Atomicity, Consistency, Integrity, and Durability are not challenges with a flat file, then go with a flat file.
For me, the line is crossed once I have to query my data in ways that involve more than a single relationship. Relating two flat data structures on disk is fairly simple, but once we get beyond that, a set-based language like SQL and formal database relationships actually reduce complexity.
I think at some point you'll miss the querying capabilities of a database, but you can consider some minimalistic database alternatives:
SQLite (Great, almost SQL-92 standard compliant)
shsql
SQL Server Compact
I would only write my own on-disk format under very special circumstances. Reusing someone else's code is nearly always faster.
For relational data, I would use SQLite. For key/value pairs, I would use BerkeleyDB (perhaps via KiokuDB). For simple objects, I would use JSON or YAML, but only if I only had a few.
With SQLite and BDB, "a real database" is literally two lines of code away. It is hard to beat that.
The problem with small projects is that they become bigger before we know it. And once they do , we start missing the sql capabilities.
Always design such that a db can be utilized later on if required without ripping apart half of the application.
It depends entirely on the domain-specific application needs. A lot of times direct text file/binary files access can be extremely fast, efficient, as well as providing you all the file access capabilities of your OS's file system.
Furthermore, your programming language most likely already has a built-in module (or is easy to make one) for specific parsing.
If what you need is many appends (INSERTS?) and sequential/few access little/no concurrency, files are the way to go.
On the other hand, when your requirements for concurrency, non-sequential reading/writing, atomicity, atomic permissions, your data is relational by the nature etc., you will be better off with a relational or OO database.
There is a lot that can be accomplished with SQLite3, which is extremely light (under 300kb), ACID compliant, written in C/C++, and highly ubiquitous (if it isn't already included in your programming language -for example Python-, there is surely one available). It can be useful even on db files as big as 1GB, possible more.
If your requirements where bigger, there wouldn't even be a discussion, go for a full-blown RDBMS.
For the kind of applications you are developing in bioinformatics, you are often doing one-shot applications (often scripts that define a workflow of calculations) that answer a specific questions, and you are not likely to be reusing these applications after you answered your question.
Often, you should therefore avoid creating databases to store the results, as after all you are not going to use their features very much.
You will probably be querying some webservices, files, or databases, run some local algorithms on the data gathered from different sources, and produce some tabular or structured output format (xml, json, etc).
For that, I would suggest you to use workflow tools like Knime (or a commercial solution like Inforsense KDE, Accelrys's Pipeline pilot, or Snaplogic, as they allow you to query data in a variety of formats and locations (rdbms, flat files, webservices), run algorithms, and build powerful web apps that allow you to easily publish your workflows to your users and let them interact at specific points).
If your prototype "grows" and you have to build more functionality on top of the data your workflows output, and if the output of your prototype is not likely to change everyday, then it's a wise decision to store a subset of the results in a database. This allows you to plug in powerful reporting tools like BusinessObjects, Crystal reports, jasper reports or whatever reporting solution available out there and show data to your users in a better shape than a spreadsheet or a csv file.
Finally, some development frameworks will make your choices more obvious : if you build a web application using an MVC framework, it is likely that your data will reside in an RDBMS (but please, don't put genomic sequences in a table column :-)).
All in all, it's a case by case choice, depending on your needs for each particular application.
In software I can usually get away with storing values in a XML configuration file or in the registry, e.g. software options. Once I need to persist objects I move to a database because the upfront cost is not that bad compared to the long term effects that relations and reporting can offer.
For bioinformatics you may be interested on that: Blast on DB. The guy who is working on that is a friend of mine and has a work on fast similarity sequence search, he found out to make his own binary storage better than using databases at this point.
I don't know specific details about his solution but you probably can exchange one or two ideias mailing the guy, even sharing code.
Do you need/want SQL queries?
Are multiple people going to want to access the data?
Is your data relational?
If you answered no to those questions, you (probably) don't need a full on database.
First, I'd consider:
How large will the database initially be: # of tables, # of rows
How quickly will it grow?
Is the data frequently queried?
If I were to create a personal recipe app, for example, I know I might add 50 favorite recipes to start and add no more than 5 recipes a year. With that being said, I could easily get by without a database since the size of the data store will have minimal impact on queries.
That said, I would probably use a database for any application where data entry and queries occur (even a small personal recipe app). I don't think it adds a lot of overhead especially when your framework (e.g. Rails) allows you to keep your database dumb (primarily tables, indexes, and constraints). It alleviates the chance that I'll have to eventually port to a database if I decide to scale up.
If you know the format of your data, flat files, if faster/easier to develop with, will be fine. If you expect your record formats to change frequently during development then I'd suggest that ALTER TABLE is your friend. Flat files will also tend to be faster (if you care about speed) unless you expect to implement the equivalent of joins across many combinations of files.
The real benefit of using a RDBMS during development is the flexibility with which you can modify your data schema and the ease with which you can access your data via queries.
Good design will ensure that you keep your data access layer relatively isolated (because of separation of concerns) so it should be a fairly straightforward (if tedious) matter to rework to a database later should it be worthwhile. Or, of course, if you use a database to develop your structures you may subsequently take the app back to flat/indexed files once those structures are crystallized in order to gain performance.
Use whatever persistence technology you're most comfortable with, and scales sufficiently.
YAGNI at least means "Don't add a new technology to your personal stack unless you can't be productive with whatever is already there."
For many (most?) of us, our comfort zone for data persistence is SQL. For some, it might be XML. Just don't write your own until (see paragraph 2).
As someone also doing research in Bioinformatics, I would suggest NOT using a database for these kinds of prototype projects unless you are sure it needs it. If you are on the fence, go with the databaseless solution and stick with flat files. It is also important to note that traditionally Bioinformatics researchers have go the flat file route, which means there are well defined file formats for most types of data in the feild. If you decide to go with a database solution, it may hurt your compatibility with existing research projects.
Our company has a point of sale system with many extras, such as ordering and receiving functionality, sales and order history etc. Our main issue is that the system was not designed properly from the ground up, so it takes too long to make fixes and handle requests from our customers. Also, the current technology we are using (Progress database, Progress 4GL for the language) incurs quite a bit of licensing expenses on our customers due to mutli-user license fees for database connections etc.
After a lot of discussion it is looking like we will probably start over from scratch (while maintaining the current product at least for the time being). We are looking for a couple of things:
Create the system with a nice GUI front end (it is currently CHUI and the application was not built in a way that allows us to redesign the front end... no layering or separation of business logic and gui...shudder).
Create the system with the ability to modularize different functionality so the product doesn't have to include all features. This would keep the cost down for our current customers that want basic functionality and a lower price tag. The bells and whistles would be available for those that would want them.
Use proper design patterns to make the product easy to add or change any part at any time (i.e. change the database or change the front end without needing to rewrite the application or most of it). This is a problem today because the Progress 4GL code is directly compiled against the database. Small changes in the database requires lots of code recompiling.
Our new system will be Linux based, with a possibility of a client application providing functionality from one or more windows boxes.
So what I'm looking for is any suggestions on which database and/or framework or programming language(s) someone might recommend for this sort of product. Anyone that has experience in this field might be able to point us in the right direction or even have some ideas of what to avoid. We have considered .NET and SQL Express (we don't need an enterprise level DB), but that would limit us to windows (as far as I know anyway). I have heard of Mono for writing .NET code in a Linux environment, but I don't know much about it yet. We've also considered a Java and MySql based implementation.
To summarize we are looking to do the following:
Keep licensing costs down on the technology we will use to develop the product (Oracle, yikes! MySQL, nice.)
Deliver a solution that is easily maintainable and supportable.
A solution that has a component capable of running on "old" hardware through a CHUI front end. (some of our customers have 40+ terminals which would be a ton of cash in order to convert over to a PC).
Suggestions would be appreciated.
Thanks
[UPDATE]
I should note that we are currently performing a total cost analysis. This question is intended to give us a couple of "educated" options to look into to include in or analysis. Anyone who could share experiences/suggestions about client/server setups would be appreciated (not just those who have experience with point of sale systems... that would just be a bonus).
[UPDATE]
For anyone who is interested, we ended up going with Microsoft Dynamics NAV, LS Retail (a plugin for the point of sale and various other things) and then did some (and are currently working on) customization work on top of that. This setup gave us the added benefit of having a fully integrated g/l system, which our current system lacked.
Java for language (or Scala if you want to be "bleeding edge", depending on how you plan to support it and what your developers are like it might be better, but also worse)
H2 for database
Swing for GUI
Reason: Free, portable and pretty standard.
Update: Missed the part where the system should be a client-server setup. My assumption was that the database and client should run on the same machine.
I suggest you first research your constraints a bit more - you made a passing reference to a client using a particular type of terminal - this may limit your options, unless the client agrees to upgrade.
You need to do a lot more legwork on this. It's great to get opinions from web forums, but we can't possibly know your environment as well as you do.
My broad strokes advice would be to aim for technology that is widely used. This way, expertise on the platform is cheaper than "niche" technologies, and it will be easier to get help if you hit a brick wall. Of course, following this advice may not be possible if you have non-negotiable technology already in place at customers.
My second suggestion would be to complete a full project plan, with detailed specs and proper cost estimates, before going with the "rewrite from scratch" option. Right now, you're saying that it would be cheaper to rewrite the system than maintain it, and you don't really know how much it would cost to re-write.
I suggest you use browser for the UI.
Organize your application as a web application.
There are tons of options for the back-end. You can use Java + MySQL. Java backend will save you from windows/linux debate as it will run on both platforms. You won't have any licensing cost for both Java and MySQL. (Edit: Definitely there are a lot of others languages that have run-times for both linux & windows including PHP, Ruby, Python etc)
If you go this route, you may also want to consider Google Web Toolkit (GWT) for creating the browser based front-end in a modular fashion.
One word of caution though. Browsers can be pesky when it comes to memory management. In our experience, this was the most significant challenge in doing browser based POS You may want to checkout Adobe Flex that runs in browser but might be more civil in its memory management.
What is CHUI? Character-UI, as in VT terminals? Or even 3270 style?
It sounds like you need a 3-tier system - the database backend, a middle-layer that runs the bulk of the back-end business processes, and a front-end layer for the CHUI / GUI / data-gateway.
All three layers can reside on one machine; or you can distribute the tiers out to various servers. The front-end layer would control the actual terminals, whether they are VT-terminals, or a web-browser, or a custom-written 'client' application.
Make sure you have considered the hardware needs here -- are you going to have barcode scanners, cash drawers, POS debit/credit terminals, et cetra? If you are using a standard browser, it might be hard to reliably integrate those items. (At the very least, you're likely going to have to write special applets to handle them.)
Finally, consider the possibility of a thin-client technology on Windows. It greatly simplifies system management, since you only have to upgrade the software centrally. Thin-client PC's are cheap -- sub $200.
Golden Code Development (see www.goldencode.com) has a technology that does automated conversion of Progress 4GL (the schema and code... the entire application) to a Java application with a relational database backend (e.g. PostgreSQL). They currently support a very complete CHUI environment and they do refactor the code. For example, the conversion separates the UI, the data model and the business logic into separate Java classes. The entire result is a drop-in replacement that is compatible with the original (users don't need retraining, processes don't need to be modified, the data is migrated too). This is possible because they provide an application server and a set of runtime classes that provide that compatibility. The result of the automated conversion is not something that needs further editing before you can compile and run it. True terminal support is included so hardware terminals still work (it requires a small JNI library to access NCURSES from Java). All the rest of the code in the runtime is pure Java. No Progress Software Corp technology is used in the resulting system and it runs on Linux.
At least one converted system is already in production, running a 24 by 7 mission critical environment. It is a converted ERP system that their mid-sized pilot customer uses to run their entire business.