For all of you working with Informix in combination with IBM Websphere, the following IBM RedPaper might be interesting and helpful. It covers the definition of data sources and contains a good description for performing those tasks in Websphere with IBM Informix as database backend:

When an application or WebSphere® component requires access to a database, 
that database must be defined to WebSphere as a data source. Two basic 
definitions are required. First, a JDBC™ provider definition defines an 
existing database provider, including the type of database access that it 
provides and the location of the database vendor code that provides the 
implementation. The second requirement is a data source definition that 
defines which JDBC provider is to be used, the name and location of the 
database, and other connection properties. This paper shows how to create 
these definitions.

IBM RedPaper: Accessing Databases from WebSphere