Slide 7 of 42
Notes:
Sequence charts in Catalysis show occurrences of use-cases. The vertical bars are objects, and the horizontal bars are interactions between them ó that is, use-case occurrences. (Messages between objects within a program are an elementary form of use-case
The objects in the diagram should be instances of the types in the type model; and the horizontal bars should be instances of use-cases. (This is one of the ways in which Catalysis interrelates UML models.)
Refinement can be thought of as expanding a vertical and/or horizonal bar: ëbuyí becomes a sequence of smaller interactions. We have also refined Vendor into different departments, and shown how the Purchaserís interactions are actually with each of them
Similarly, when I say ìthe ATM asked for my ID and I typed 4 at itî I could actually go into more detail: ìthe ATMís screen asked for my ID and I typed 4 at its keyboardî.
Itís worth emphasising that all these views are simultaneously true: itís just that some of them contain more detail about the truth than others.
The sequence charts show the two dimensions of decomposition fairly clearly. You can imagine continuing the process, breaking each department into people and support software, and including interactions between the people and the software; and also breaki
(However, we donít usually design software in this top-down fashion! Thatís just a convenient way of understanding the refinement relationship.)
