LECTURE 5 4/2/16 1

Functional decomposition 2

A few words on “assumptions” Assumptions arise when there is uncertainty about interpreting observations There are different ways of interpretation There are options For example, in case of a system dealing with books, should the “author” be an object on its own or an attribute of the book object (i.e. author’s name)? It depends: for a library system that might suffice, for a publisher they might need to know a lot about each author having contract with them

A few more words on “assumptions” Do not confuse it with Facts, that may be observed – even if it is the result of analysis Design decisions – which you make (and record) as you progress

More on Activity Diagrams A good tool for illustrating the logical flow of activities that take place between the system and the outside world and the outside world or within the system among its components Activity diagram has two unique tools i.e. swimlanes and synchronisation bar 5

Activity Diagrams - Swimlanes This is a vertical partition that organises responsibilities for actions. Not limited to objects in a systems Swimlanes can also represent divisions within an organisation E.g. Inventory Shipping Sales Accounting 6

Swimlane Diagrams Allows the modeler to represent the flow of activities described and at the same time indicate which actor (if there are multiple actors involved in a specific use-case) or class has responsibility for the action described by an activity rectangle

Example Activity Diagram Commuter use a vending machine to buy train tickets. The ticket vending machine will request trip information from a Commuter. Based on the this information, the machine will calculate payment due and request payment options, these include payment by cash or by debit/credit card. After payment is complete, the ticket is dispensed to the Commuter. 8

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Summary Activity Diagrams Popular form of dynamic modelling Good at representing the complexities of logical flow Swimlanes and synchronisation help to add a level of complexity to the diagram beyond flowcharts and sequence diagrams 10