Unified Modeling Language (UML)

The Unified Modeling Language was build on the bases of object oriented analysis and drafting methods. It is used to model the structure and sequence of processes.

Use case diagram

A use case diagram represents the relation between actors and use cases.

This type of diagram does not care about the implementation, it just represents the interaction with a system; hence it is not a design document (strictly speaking).

The use case describes a certain activity that is supported by the system and gets denoted by a ellipse which includes the name of the activity ("order item" for example).

Actors can "use" these use cases to interact with a system; these relations get represented by a line between actor and use case.

State diagram

A state diagram describes a set of states which are connected by a set of actions. Each state holds it's own variables. If a certain condition is met we transition from one state to another.

States are represented by rounded rectangles which have a name, variables and actions.

Transitions are arrows that point from one state to another.

Class diagram

A class diagram represents the relation between individual classes (objects) and the system as a whole.

This relation could look something like business customer and private customer are both customers (inheritance). One customer can have many orders. Each order can have exactly one status.

A class gets represented by a rectangle wich can have multiple attributes and functions. The relation between these classes are denoted by a line. At each end of the line can be arrow heads or other quantitative information like 1 x n.

Sequence diagram

A sequence diagram models the exchange of information between objects; this happens in a set sequence.

The order of elements is important, since we want to describe in which order something happens.

Each object is surrounded by a dotted line which extends downwards. In the middle of each dotted line is a bar which represents some sort of activity.

The directed connections between these bars denote the exchange of information. Such information could be "message ->" "<- response".