WEEK 7 CS2002 Software Development and Management: Activity Diagrams

Brunel University of London

• Course: CS2002 Software Development and Management

• Instructor: Dr. Yani Xue

The Activity Diagram

• Focus on visualizing the flow of activities in a system, particularly in software processes.

Reference Material

• Textbook:

  • "UML @ Classroom: An Introduction to Object-Oriented Modeling"

  • Authors: Martina Seidl, Marion Scholz, Christian Huemer, Gerti Kappel

  • Publisher: Springer Publishing, 2015

  • ISBN: 3319127411

Content Overview

• Key components of the discussion include:

  • Introduction and purpose of Activity Diagrams

  • Basic elements and their functions

  • Object nodes and their roles

  • Central buffers and data stores for information management

  • Connectors to enhance diagram readability

  • Event-based actions and call behavior actions

  • Use of partitions in diagrams

  • Exception handling strategies

Introduction to Activity Diagrams

• Purpose: Model the processes within a system, focusing on procedural aspects.

• Related concepts:

  • Business process languages

  • Petri net token concept for describing concurrent processes

• Broad application across object-oriented and non-object-oriented system modeling.

Levels of Granularity

• User-defined behavior can be specified at multiple levels:

  • Business process functions

  • Use case action flows

  • Detailed instruction behaviors for operations

Understanding Activities

• Definition:

  • Directed graph where:

    • Nodes represent actions

    • Edges indicate control and object flow necessary for execution

• Optional elements:

  • Parameters

  • Pre- and postconditions

Action Specifications

• Fundamental unit for defining user behavior:

  • Actions are atomic but can be aborted.

  • Can be described using natural language or programming languages.

  • Notation for predefined action types includes event-based actions and call behavior actions.

Edges: Connecting Components

• Functionality:

  • Connect activities and define execution order.

• Types of edges:

  • Control flow edges: Specify order of execution between nodes.

  • Object flow edges: Facilitate data/object exchange between nodes, showing dependencies.

Control and Object Flow

• Control flow connects actions sequentially, while object flow illustrates data dependencies.

Conditions and Guards

• Guards (conditions) determine flow continuity; execution continues if conditions in brackets evaluate to true.

Tokens

• Managing execution:

  • Tokens regulate execution permission for actions.

• Process: Action receiving a token can execute, then transfers token to subsequent actions, contingent upon guard evaluations.

• Types of tokens:

  • Control tokens (execution permissions)

  • Object tokens (carry data)

Activity Initialization

• Initial Node:

  • Commences activity execution, generating tokens for outflow.

  • Supports multiple nodes for modeling concurrent activities.

Activity Termination

• Final Nodes:

  • Activity Final Node: Terminates all execution paths upon receiving first token.

  • Flow Final Node: Ends specific execution paths without affecting others.

Decision Nodes

• Define alternative paths with guard conditions facilitating flow selections based on evaluations.

Merge Nodes

• Consolidate alternative paths into a single flow, capable of modeling loop structures.

Parallelization Nodes

• Split execution paths into concurrent subpaths, duplicating tokens for distribution.

Synchronization Nodes

• Merge concurrent paths, waiting for tokens at all inflows before processing and passing on control tokens.

Example Flow

• Illustrative examples demonstrate complex interactions, decision-making and parallel workflows within the context of attending lectures and registering for assignments.

Object Nodes

• Contain data eligible for flow, referencing data exchange, with additional typological information as needed.

Central Buffers and Data Stores

• Central Buffer:

  • Temporary storage for object tokens, Read operations delete token from memory.

• Data Store:

  • Permanent memory for saving object tokens, allowing copies for distribution.

Weight of Edges

• Minimum token requirement for action execution; defaults and variations signify token consumption logic.

Connectors

• Used to connect actions spread apart, enhancing diagram readability.

Event-Based Actions

• Different actions, such as sending signals or accepting events, include specific notations and illustrate varied interaction triggers within the system.

Call Behavior Actions

• Allows for the hierarchical structuring of actions, promoting clarity and reusability of modeling components.

Partitions

• Organizational units in diagrams, grouping nodes and edges for clarity reflecting responsible roles or units.

Exception Handling

• Defined responses to error situations, employing exception handlers that replace actions, ensuring continuity of process.

• Interruptible Activity Region:

  • Categorizes actions that terminate upon specific event occurrences, triggering alternative behaviors.

Notation Elements for Diagramming

Basic Symbols

• Action Node: Represents an entity executing an action.

• Activity Node: Depicts broader processes that can be subdivided.

• Final Nodes: Marks the end of execution flows.

Advanced Symbols

• Decision/Merge Nodes: Shapes indicating branching and merging of execution paths.

• Parallelization/Synchronization Nodes: Nodes for concurrent execution path management.

Additional Symbols

• Object Nodes: Represent data exchange points within the flow.

• Exception Handlers: Depict responses to faults in execution.