Archive for January, 2010

January 18, 2010

HOWTO: ArgoUML and archgenxml

ArgoUML and archgenxml are great utilities to have around while doing Plone development. However, if you go by the documentation (whatever little exists), be prepared for a long night and a pot of hot coffee handy. I hope to maintain this page with issues I encountered (and solutions wherever found).


File “Plone/Python-2.4/lib/python2.4/site-packages/xmiparser-1.4-py2.4.egg/xmiparser/”, line 697, in calcDatatype
raise ValueError, ‘datatype %s not defined’ % typeid
ValueError: datatype archgenxml_profile.xmi#16a8d020-4c0a-58ce-993f-e6306abf0bbf not defined


Save your project as “.zargo” file format and pass that to archgenxml instead – like “archgenxml test.zargo”.

Comment: You’d have expected that whoever thought of something like archgenxml would have enough sense to print out a warning – seems like an obvious trap to fall into (going by the documentation).

Problem: You want to override the default view of a custom content type. That is “content_type/view” should resolve to your defined view.


Setting up things in argouml to override the view is simple –

1. Select the class you want to set the default view. It is important that you click on the class name – selecting any other attribute or method will NOT work.

2. Click on the “Tagged Values” tab.

3. Select the default_view tag from the list of drop downs. Set the value of the tag to resolve to your defined view.

4. Save project and run archgenxml to setup the Plone product.

Comment: In case you cannot get this to work, just follow these simple steps to ensure that you haven’t been victimized by one of argouml’s quirks.

Step1. Open up the profiles/default/types/your_content_type.xml

Step2. Search for the line which contains the following declaration

<property name=”default_view”>your_default_view</property>

it should be set to your default view. If not, you need to go back to step 1 of the solution above and really ensure you click on the class name and start over again.

Next we will see how to actually provide the view.

January 9, 2010

Cloudy combo Google App Engine and Amazon S3 combo pack:

Google App Engine provides you a ready to use environment to build and host web applications. The hosting environment is secure and made highly available by the google’s cloud computing infrastructure.

While GAE provides you such a strong platform to build and host web applications, it has it’s own limitations as well. While Google’s infrastructure gives you abundant computing power but not the  case with storage which you would expect if you are developing web applications which require a large amount of flexible secondary storage as well, for that even the applications requiring moderate amount of secondary storage to store the files.

Coming to the actual point, GAE has a limitation of allowing applications to store not more than 10MB of a single large file on it’s server. This may not be a problem for some of the web applications. This is a serious issue for many web applications which assume sufficiently large underlying storage, given these days secondary storage is available in abundance at cheap rates. Some of the developers and users are shying away from using GAE as a platform for their web application development and hosting only because of this reason. And to make life hard google does not have a paid service either to work around this issue.

What are these web application developers supposed to do? Switch to something else which offers sufficient storage along with computing power. The other better options available are Amazon EC2 and VPS. Give me a break. Why do we want to run away from the problem? Well, look around. Amazing Amazon is there to help you out. We need to think creatively and be selective when making decisions about technology these days. There are a bunch of technologies lying around. It is just a matter of selecting and integrating the two technologies and using them to satisfy needs. I am not trying to promote any specific cloud here, but to highlight the fact that GAE and Amazon S3 work really well. And it turns out to be a cost effective solution.

GAE provides the development and hosting platform for you web applications at free of cost while Amazon S3 provides you reliable, powerful and abundant storage at cheaper rates. GAE and Amazon S3 together can do wonders.

Enough of theory, let me explain it to you with a practical example.
We, at BYGSoft, had a requirement to develop a web application for one of our clients. It was a simple web application which will work as a download portal for it’s customers. We chose GAE as a development and hosting platform for web application and Amazon S3 as the back end storage.
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