 The structuralist conception of model-representation originated in the so-called semantic view of theories that came to prominence in the second half of the 20th century (see the SEP entry on the  structure of scientific theories  for further details). The semantic view was originally proposed as an account of theory structure rather than scientific representation. The driving idea behind the position is that scientific theories are best thought of as collections of models. This invites the questions: what are these models, and how do they represent their target systems? Most defenders of the semantic view of theories (with the notable exception of Giere, whose views on scientific representation were discussed in the previous section) take models to be structures, which represent their target systems in virtue of there being some kind of morphism (isomorphism, partial isomorphism, homomorphism, …) between the two.