ACS2913 Software Requirements Analysis and Design Instructor: Victor Balogun

OBJECT BEHAVIOR

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Object Behavior –State Machine Diagram

Each class has objects that may have status conditions or “states”

Object behavior consists of the various states and the movement between these states

State – a condition during an object’s life when it satisfies some criterion, performs an action, or waits for an event

Transition – the movement of an object from one state to another

A “State machine” is an abstract concept (a model) to identify objects behaving like a “Machine” that can be in one of many finite states.

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State Machine Diagram

A state machine is anything that can have different states. ◦ In our case we will refer to the different states of an object

◦ The states are the different combinations of information that an object can hold and not how they behave

Applications of a State machine Diagram◦ Depicting event-driven objects in a reactive system.

◦ Illustrating use case scenarios in a business context.

◦ Describing how an object moves through various states within its lifetime.

◦ Showing the overall behavior of a state machine or the behavior of a related set of state machines.

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State Machine DiagramState Machine Diagram – a diagram which shows the life of an object in states and transitions

Origin state – the original state of an object before it begins a transition

Destination state – the state to which an object moves after completing a transition

pseudostate – the starting point in a state machine diagram. Noted by a black circle.

action-expression – some activity that must be completed as part of a transition

guard-condition – a true/false test to see whether a transition can fire

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State Machine for a Printer

Syntax of transition statement

◦ transition-name (parameters, …) [guard-condition] / action-expression5SYSTEMS ANALYSIS AND DESIGN IN A CHANGING WORLD, 7TH EDITION – CHAPTER 4 ©2016. CENGAGE LEARNING. ALL

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Concurrency in a State Machine Diagram

Concurrent states – when an object is in one or more states at the same time

Path – a sequential set of connected states and transitions

Concurrent paths – when multiple paths are being followed concurrently, i.e. when one or more states in one path are parallel to states in another path

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Composite States

State containing other states and transitions

Printer can be On and either Idle or Working

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Concurrent Paths

Multiple paths in composite state◦ Printer On paths are independent

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Printer with Concurrent Paths

Concurrent paths often shown by synchronization bars (same as Activity Diagram)

Multiple exits from a state is an “OR” condition.

Multiple exits from a synchronization bar is an “AND” condition.

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Creating a State Machine DiagramSteps

1. Review the class diagram and select classes that might require state machine diagrams

2. For each class, make a list of status conditions (states) you can identify

3. Begin building diagram fragments by identifying transitions that cause an object to leave the identified state

4. Sequence these states in the correct order and aggregate combinations into larger fragments

5. Review paths and look for independent, concurrent paths

6. Look for additional transitions and test both directions

7. Expand each transition with appropriate message event, guard condition, and action expression

8. Review and test the state machine diagram for the class

◦ Make sure state are really state for the object in the class

◦ Follow the life cycle of an object coming into existence and being deleted

◦ Be sure the diagram covers all exception condition

◦ Look again for concurrent paths and composite states

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RMO – Creating a State Machine DiagramSteps -- SaleItem

1. Choose SaleItem. It has status conditions that need to be tracked

2. List the states and exit transitions

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RMO – Creating a State Machine DiagramSteps -- SaleItem

3. Build fragments – see figure below

4. Sequence in correct order – see figure below

5. Look for concurrent paths – none

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RMO – Creating a State Machine DiagramSteps -- SaleItem

6. Add other required transitions

7. Expand with guard, action-expressions etc.

8. Review and test

Below is the final State Machine Diagram

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RMO – Creating a State Machine DiagramSteps -- InventoryItem

1. Choose InventoryItem. It has status conditions that need to be tracked

2. List the states and exit transitions

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RMO – Creating a State Machine DiagramSteps -- InventoryItem

3. Build fragments – see figure below

4. Sequence in correct order – see figure below

5. Look for concurrent paths – see figure below

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RMO – Creating a State Machine DiagramSteps -- InventoryItem

6. Add other required transitions

7. Expand with guard, action-expressions etc.

8. Review and test

Below is the final State Machine Diagram

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Use Case to Process a Sale

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We can construct a State Machne Diagram showing states for this use case

Process Sale

Waiting For Sale; Entering Items; Waiting For Payment are System states that arise in the Process Sale use case.

Transitions are system events … the diagram clearly shows when events, such as makeNewSale, are legal.

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Bank Account Example

We’ll develop the example by considering each state, and the transitions that can occur when an account is in that state.

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Four States:

active

overdrawn

closed

deleted

Bank Account Example An account begins by being Active. Once in the Active state, the account can remain active, become overdrawn, or be closed.

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Bank Account Example

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Bank Account Example

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Bank Account Example

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