Posts Tagged ‘MDA’

The future of MDA

April 15, 2009

I have discovered MDA, through the AndroMDA project, about 4 years ago. The idea of automatically generating some repeated patterns, the amaizing power of generating a database structure, Entity Beans or Hibernate linkage files by only providing an UML diagram model, the capability of keeping a minimal description (the UML document) have all convinced me not only to learn how AndroMDA works, but also to start using it in production.

As for today, I have used AndroMDA in at least 6 distinct projects. I didn’t use the clasical path shown by AndroMDA. I have chosen atomic Maven projects either 100% UML generated or 100% manual. No file was manually changed after generation, this pattern proved to be desastruous in practice.

I am wondering what is the today future of the MDA. As I was warning 5 month ago a developer of ArgoUML about a minor issue, they exclamated “wow, you are still using AndroMDA!”. So what is the next MDA product? Any answers from the community?


Ajax and J2EE or how simple things became complicated

April 15, 2008

Last days I have started a new project. It’s about finance, budgeting and management. The UML class diagrams have already dozen of entities, which translate in dozen of tables.

As a big fan of MDA, after designing the model I have immediately generated the database structure, Hibernate POJOs and EJB (at that moment, still undecided which direction should be followed). The whole work took about 30 minutes, with Apache Maven and AndroMDA.

But what about the user interface? AndroMDA offers something similar to “scaffolding” of Ruby on Rails. My problem with this scaffolding is that a number of files are only generated once, subsequent changes will not reflect them self on the existing generated sources. With other words, it sucks, since I am sure my model is not final, customers will perform lots of changes until it goes into production.

Following the speculation path (yes, I do use Agile PM), I have taken the simplest entity, which only has three columns (2 strings and a boolean) and attempted to see how easy is to have an AJAX based table to perform CRUD (create read update delete) on this table.

The first choice would be ZK, an open source AJAX library. Because of their GPL license, which forces me either to publish my sources or to acquire their commercial license, I have considered another AJAX engine, RichFaces.

RichFaces has a nice comprehensive demo and a bad written manual; as a beginner in RichFace, I find it unreadable because of cyclical definitions (such as: “bypassUpdates attribute allows to bypass the Update Model phase” and no definition of Update Model is given) and employment of too many undefined concepts. Maybe my further contacts with RichFaces will allow me to read their manual with other eyes. I have found a nice sample explaining tables with editable cells. It looks nice, but, it doesn’t store the changed data! The inquiry on the RichFaces forum had was immediately answered by some more advanced user, which acknowledged the issue and provided a solution. I was just one step away of abandoning the RichFaces track and moving to other AJAX engine, but their vibrant community convinced me indirectly not to switch.

After successfully building and running the web application within Maven, my approach is to connect the table to a list of EJB3 entities. The plan is to build a transaction on each change since it is not usual that users will perform a lot of changes here, and this avoids the usage of a “Commit” button people can forget to press while jumping to another page.
I also plan to have a “New Item” and “Delete Item” button. Delete seems to be easy to implement, while adding a new item can be a pain – since the table has a paged scroller and after adding the new item, the scroller should jump at its page. Also, the newly inserted item has an “uncommitted” state until all of its items are filled with data.

Well, after reviewing the findings in this loop, I remember 18 years old technology named “FoxPro”. This technology powered my first business. It didn’t have funny programming features such objects, no enterprise capabilities (they were added afterwards). It doesn’t run through a web interface or even within a windowing system (but on a 80×25 character screen). This tool could easily handle an editor with millions of entries on an Intel 80286 processor based machine, and this with a simple BROWSE command. Now, I read blogs of ajaxians complaining about performance of Ajax tables containing 500 entries! If FoxPro would be hypothetically transformed in a client server engine, considering an average refresh rate of the screen to one second, it would use only a 32kbit bandwidth to run through a terminal. An ajax application uses much more bandwidth, even in the context Ajax reduces the amount of data transacted (and if properly coded, the number of transactions) between server and client.

So, what is the direction our technology evolution follows? Do we sacrifice the simplicity of design and implied simplicity of deployment and usability to acquire some obscure targets such as “transactionability” or “service oriented architecture”? I see now more than ever web sites crashing with errors like “Invalid Transactional State” or “Session Expired” (although I didn’t time it out). I try to imagine what platform did the developers of these sites use and what mistake they done and the answer is from day to day harder to find.