I need to create some relationship and data flow diagrams for the project I am working on, but I hate using software such as Visio and Dia, since the diagrams never look the way I want them to, the controls never behave in an intuitive way etc. Is there a software package, that would allow me to define relationships between entities in script of some sort and than render it into an image file or a PDF or something?
You can look into the DOT language. It's technically for graphs, but might suit your purposes.