Systems Analysis and Synthesis

3.5. Analysing States

Consider the states of a copy of a Book from the point of view of a librarian. The important states of a copy might be: On Order, Shelved, On Loan, Archived, and Scrapped. From this point of view, although much detail has been omitted, the states of the book are discrete and finite in number. In contrast, a book retailer might consider a different set of states to be important: On Order, In Stock, Sold, and Damaged. Let us focus first on the librarian’s view.

Libraries keep track of individual copies of books. The first action of the librarian would be to Order a copy from a supplier. After this, the copy would be On Order. Prior to this, the copy would be in its Null state, one that is of no particular interest to the library, ...