Software Engineering Ch 5

UML diagram types

Activity diagrams, which show the activities involved in a process or in data processing . Use case diagrams, which show the interactions between a system and its environment. Sequence diagrams, which show interactions between actors and the system and between system components. Class diagrams, which show the object classes in the system and the associations between these classes. State diagrams, which show how the system reacts to internal and external events.

System perspectives

An external perspective, where you model the context or environment of the system. An interaction perspective, where you model the interactions between a system and its environment, or between the components of a system. A structural perspective, where you model the organization of a system or the structure of the data that is processed by the system. A behavioral perspective, where you model the dynamic behavior of the system and how it responds to events.

Use of graphical models

As a means of facilitating discussion about an existing or proposed system Incomplete and incorrect models are OK as their role is to support discussion. As a way of documenting an existing system Models should be an accurate representation of the system but need not be complete. As a detailed system description that can be used to generate a system implementation Models have to be both correct and complete.

Behavioral models

Behavioral models are models of the dynamic behavior of a system as it is executing. They show what happens or what is supposed to happen when a system responds to a stimulus from its environment. You can think of these stimuli as being of two types: Data Some data arrives that has to be processed by the system. Events Some event happens that triggers system processing. Events may have associated data, although this is not always the case.

Process perspective

Context models simply show the other systems in the environment, not how the system being developed is used in that environment. Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries Process models reveal how the system being developed is used in broader business processes. UML activity diagrams may be used to define business process models.

Interaction models

Modeling user interaction is important as it helps to identify user requirements. Modeling system-to-system interaction highlights the communication problems that may arise. Modeling component interaction helps us understand if a proposed system structure is likely to deliver the required system performance and dependability. Use case diagrams and sequence diagrams may be used for interaction modelling.

Event-driven modeling

Real-time systems are often event-driven, with minimal data processing. For example, a landline phone switching system responds to events such as 'receiver off hook' by generating a dial tone. Event-driven modeling shows how a system responds to external and internal events. It is based on the assumption that a system has a finite number of states and that events (stimuli) may cause a transition from one state to another.

Sequence diagrams

Sequence diagrams are part of the UML and are used to model the interactions between the actors and the objects within a system. A sequence diagram shows the sequence of interactions that take place during a particular use case or use case instance. The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these. Interactions between objects are indicated by annotated arrows.

Structural models

Structural models of software display the organization of a system in terms of the components that make up that system and their relationships. Structural models may be static models, which show the structure of the system design, or dynamic models, which show the organization of the system when it is executing. You create structural models of a system when you are discussing and designing the system architecture.

System modeling

System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system. System modeling has now come to mean representing a system using some kind of graphical notation, which is now almost always based on notations in the Unified Modeling Language (UML). System modeling helps the analyst to understand the functionality of the system and models are used to communicate with customers.

State machine models

These model the behaviour of the system in response to external and internal events. They show the system's responses to stimuli so are often used for modelling real-time systems. State machine models show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one state to another. Statecharts are an integral part of the UML and are used to represent state machine models.

Use case modeling

Use cases were developed originally to support requirements elicitation and now incorporated into the UML. Each use case represents a discrete task that involves external interaction with a system. Actors in a use case may be people or other systems. Represented diagrammatically to provide an overview of the use case and in a more detailed textual form.