16. dialogue notations and design


Develop the JSD diagram in Figure 16.14, expanding the various nodes until you get to basic operations such as 'prompt "login"' or 'user types in password'. Expand the 'delete employee' node using the dialog style as described in Figure 16.13, and use your imagination for the rest.


This is a fairly simple exercise, and some of the nodes are expanded here. In Figure Ex16.3.1, the login subdialog is expanded, but it assumes that the user types the correct password during the login process. To change it to accommodate incorrect passwords would be inordinately complex for two reasons. Firstly, the JSD diagram does not distinguish between user choice (whether to add or delete a record) and system choice.

JSD diagram for logging in to personnel system

Ex16.3.1 - JSD diagram for logging in to personnel system

This is evident in both the change and delete subdialogs (Figures Ex16.3.2 and Ex16.3.3).

JSD diagram for updating a record.

Ex16.3.2 - JSD diagram for updating a record

JSD diagram for record deletion subdialog

Ex16.3.3 - JSD diagram for record deletion subdialog

In each of these the actual updating of the file is put in an 'optional' box as the user may have answered 'N' (no) when asked to confirm the update. Secondly, making the dialog dependent on the password would mean that the rest of the dialog would sit under an 'option' box with another box to abort. This was acceptable in the delete and change subdialogs, but if this were applied to the login sequence, the resulting dialog would become degenerate and hide the normal hierarchical structure. This problem of whether or not to include exceptional cases and error behaviour is extremely complex. In the early stages of design it is the normal cases that one wants to consider. Later on one might refine the dialog descriptions, or alternatively annotate the normal description.

Other exercises in this chapter

ex.16.1 (ans), ex.16.2 (ans), ex.16.3 (ans), ex.16.4 (ans), ex.16.5 (tut), ex.16.6 (tut)

all exercises for this chapter