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Showing posts from 2013

YUI Cross-Domain transactions without Flash

Recently I've worked on the application making cross-domain ajax calls with YUI. While YUI offers io-xdr module for making cross-domain requests via Flash transport, it seems to me quite unnatural as it leads to unnecessary complexity. Moreover, io-xdr was marked deprecated several months ago without explicit mentioning the preferred way. An obvious alternative is using XMLHttpRequest as a transport for cross-domain requests. However, it has some limitations and undocumented pitfalls that I'd like to review in this post. Cross-Domain request using XMLHttpRequest.YUI IO Utility.YUI Datasource IO.Cross-Domain request using XMLHttpRequest
Cross-domain requests can be sent using a common XMLHttpRequest object. The only requirement is that the server must be configured to properly handle those requests. Specifically, it should set the Access-Control-Allow-Origin response header according to Cross-Origin Resource Sharing specification. For more details and good tutorials you can ref…

Analysis of network issues with tcpdump and wireshark

I've recently had to deal with the application connectivity issue (details on stackoverflow) that appeared after the migration of the application to a new server. It resulted in "Connection timed out" Java exceptions in certain cases. The answer was on the surface but I didn't know where to look at exactly. So I had to investigate and apply network sniffing tools such as tcpdump and Wireshark. Here I'd like to share my experience with the network analysis. The issue and the cause.Wireshark.Tcpdump.The issue and the cause
The following exception was thrown by Saxon XSLT processor when the document function was invoked: Caused by: org.apache.commons.lang.exception.NestableRuntimeException: net.sf.saxon.trans.DynamicError: net.sf.saxon.trans.DynamicError: java.net.ConnectException: Connection timed out at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSoc…

My first Play Framework application

My first Play Framework application has recently gone live. This time it was the Java version of the framework, next time I may move on to Scala finally. Nevertheless, I've learned a lot and will try to share some knowledge here. The application is meant for managing the data stored in the Dydra graph database (RDF & SPARQL). It's a thick client application meaning that the data loading happens in the client JavaScript layer via JSON requests, while routing and user authentication is done by means of Play Framework. Also I've made use of the RequireJS support in Play Framework for dynamic JS module loading. For the UI I've chosen a well-known YUI library. More details are following below. Application architecture.User model and authentication.Dydra database layer and SPARQL client.JavaScript logic and YUI.RequireJS module loading.Application architecture
As any web application, this one can be described in terms of MVC pattern. Play Framework encourages following …

Cocoon refactorings

I've been maintaining a complex Cocoon application for a couple of years now. Unfortunately, as the code gets older, it requires more and more time for maintenance unless you keep it clean and neat from the beginning. Finally I've found time to refactor the project gradually and I'll try to keep it this way. In this article I'm going to review the steps I've taken to improve the code and build quality.
Remove duplicated resources
I've started with removing duplicated and unused resources (mostly images and icons). Many of them were duplicated across the application in several Cocoon blocks. So I had to keep common resources in a single shared block and modify references from other blocks accordingly. For this I've added the following sitemap rule into all blocks: <map:match pattern="shared/resource/external/**"> <map:read src="servlet:shared:/resource/external/{1}"/> </map:match> This single improvement decreased th…

Handling data issues with XQuery

This post is about the good practice on how to handle the data issues with XQuery. We store a huge amount of xml data in Sedna XML database, and there happen to be synchronization issues with external systems resulting in xml data issues. One of possible consequences is that an XQuery function may receive an input parameter of an unexpected type. The limitation of the problem is that Sedna supports only XQuery 1.0 and not XQuery 3.0. As a result, try/catch expressions are not yet available for Sedna that makes handling issues harder and nastier. BTW, a while ago I created a feature request for Sedna to add support of XQuery 3.0 - you're welcome to upvote it!
Issue description
Here is the initial XQuery that simply returns the subtitle tag value. declare function vp:getMapSubtitle($vp as element(value-proposition)?) as xs:string? { data($vp/topicmeta/subtitle) }; We faced a data issue when there appeared two value propositions as an input parameter $vp. It resulted in the fo…

Extracting XML comments with XQuery

I've just discovered that it's possible to process comment nodes using XQuery. Ideally it should not be the case if you take part in designing your data formats, then you should simply store valuable data in plain xml. But I have to deal with OntoML data source that uses a bit peculiar format while export to XML, i.e. some data fields are stored inside XML comments. So here is an example how to solve this problem.
XML example
This is an example stub of one real xml with irrelevant data omitted. There are several thousands of xmls like this stored in Sedna XML DB collection. Finally, I need to extract the list of pairs for the complete collection: identifier (i.e. SOT1209) and saved timestamp (i.e. 2012-12-12 23:58:13.118 GMT). <?xml version="1.0" standalone="yes"?> <!--EXPORT_PROGRAM:=eptos-iso29002-10-Export-V10--> <!--File saved on: 2012-12-12 23:58:13.118 GMT--> <!--XML Schema used: V099--> <cat:catalogue xmlns:cat="u…