A shape-pattern schema is an organized body of knowledge about spatial relationships between shapes which describes the patterns, syntactic structure, and the characteristics of shape patterns. In this paper we show how such schema can be represented by means of chain models. We also show the advantage of this approach (relative to the previously suggested tree representations) for patterns with certain natural symmetries. To do this, we describe an example, and discuss its implementation by means of the application procedural interface of our system. Because the chain-model formulation subsumes the tree representation as a special case, the chain-model approach can also be used wherever the tree representation would be appropriate.