What is the difference between Graph Transformation and Graph Grammars ?

We generally speak of graph grammars in analogy with Chomsky grammars, i.e., if we are interested in the set of graphs generated from a given start graph by means of a set of rules. If we are interested in the transformations themselves, as a computational process, we speak of graph transformations.

What does the raven have to do with it? 

The raven has been officially introduced as a logo of a workshop in Bremen in 1990 (or so the author was told). It has been choosen for its sound of gra gra, an abbreviation for Graph Grammars, of which it seems to be an ancient fan.