Systems Analysis and Synthesis

9.2. Rule-based Systems

Consider the kernel specification of the Enrol event:

$\begin{matrix} Enrol (c, s) \Leftarrow & Candidate State (c) = Admitted; \\ Subject State (s) = Offered; \\ Filled (s) < Quota (s); \\ p = Programme (c); \\ Component State (p, s) = Offered; \\ e = (Current Semester, c, s); \\ Enrolment State (e) = Null; \\ Enrolment State {(e)}^{'} = Enrolled; \\ Mark {(e)}^{'} = null; \\ Filled {(s)}^{'} = Filled (s) + 1; \\ Balance Owing {(c)}^{'} = Balance Owing (c) + Fee (s) . \end{matrix}$

Now consider some further rules concerning possible errors. First, Candidate State might also be Graduated or Null:

$\begin{matrix} Enrol (c, s) \Leftarrow & Candidate State (c) = Null; \\ Error.No Such Admission (c) . \\ Enrol (c, s) \Leftarrow & Candidate State (c) = Graduated; \\ Error.Graduated (c) . \end{matrix}$

where Error is a program object that reports errors, ...

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Systems Analysis and Synthesis by Barry Dwyer

9.2. Rule-based Systems

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