One of the novel features of CASL, the Common Algebraic
Specification Language, designed by the CoFI group (Common
Framework Initiative) is the provision of so-called architectural
specifications for describing the static modular structure of
software systems. In this talk, a brief presentation of CASL
specifications and discussion of their refinement provides a
setting for the rationale behind architectural specifications. I
follow with some details of the features provided in CASL for
architectural specifications, hints concerning their semantics,
and simple results justifying their usefulness in the development
process. I conclude with a list of technical issues recently
resolved, as well as those yet to be resolved to make CASL
architectural specifications fully usable.