Changing Perspective From Structured to Object-oriented

Food for Thought A school play –As perceived by the producer / director –As perceived by Ms. Kenny (room 4) –As perceived by Johnny (who plays one of the three little ducks) An automated train signalling system –As perceived by the train –As perceived by the signal –As perceived by the track

… An examination –As perceived by a student –As perceived by the author(s) of the paper –As perceived by the external examiner –As perceived by the examinations office A lift –As perceived by the lift –As perceived by the lift controller –As perceived by the passenger

Structured Methodologies… Focus on the system as a whole. Incorporate end-users into their scheme. Engage with other systems when necessary. Consider the system to be bound.

Object-oriented Methodologies… Use a bottom-up approach. Consider the system as one of many possible combinations of objects. Consider the world, and the system within it, to be a set of interactions between objects. The system is scoped, rather than bound.

The Object-oriented View A system comprises: –A set of users or user roles. –A set of tasks that each user role performs. –A set of stored objects, which interact with each other to perform the tasks. –A set of user interface objects, that the user operates to enact the tasks.

Where Do We Begin? We are not using –Context Diagrams –Data Flow Diagrams –Entity Relationship Diagrams Q: How do we define the scope? A: We state what user roles we have, and what tasks they expect the system to perform for them. –i.e. with the Use Case diagram.

Model View User View Structural View Environment View Behavioural View Implementation View After Alhir,1998 ‘UML in a Nutshell’, O’Reilly

User view Problem and solution from the perspective of those individuals whose problem the solution addresses. Presents goals and objectives of problem owners. Presents solution requirements. Comprises Use Case Diagrams.

Structural View Encompasses static or structural aspects of the problem / solution. Also known as the static or Logical View. Contains –Class diagrams – specification of how the system is declared. –Object diagrams – static structure of a system at a particular time during its life.

Behavioural view definition Dynamic / behavioural aspects of a problem / solution. Also known as the dynamic / process / concurrent / collaborative view.

Behavioural view contents (1) Sequence diagrams –Describe the behaviour provided by a system to interactors, using classes that exchange messages within an interaction arranged in time sequence. Collaboration diagrams –realise components in the system. Convert sequence diagram information into a set of classes, associations and message exchanges.

Behavioural view contents (2) Statechart diagrams –Render states and responses of a class participating in behaviour –the life cycle of an object. Activity diagrams. –renders activities or actions of a class participating in behaviour. –Can describe behaviour of a class in response to internal processing –Can show the workflow through the system.

Implementation view Also known as the component or development view. Contains component diagrams. –Describe the organisation of and dependencies among software implementation components. –E.g. databases, database schemas and tables.

Environment view Also known as the deployment View Shows structure and behaviour of the domain in which the solution must be realised. Contains deployment diagrams. –describe the configuration of processing resource elements (e.g. hardware) and the mapping of software implementation components onto them.