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Questions and Answers
Why is understanding the system's context important during design?
Why is understanding the system's context important during design?
What does a system context model demonstrate?
What does a system context model demonstrate?
What is the purpose of designing the architecture of a system?
What is the purpose of designing the architecture of a system?
What commonly complicates object class identification in object-oriented design?
What commonly complicates object class identification in object-oriented design?
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Which approach can be used to identify object classes based on tangible items?
Which approach can be used to identify object classes based on tangible items?
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What is a major characteristic of the interaction model?
What is a major characteristic of the interaction model?
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Which architectural pattern organizes system components for interactions?
Which architectural pattern organizes system components for interactions?
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What is the main focus of the implementation stage in software engineering?
What is the main focus of the implementation stage in software engineering?
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Which is a benefit of buying off-the-shelf systems (COTS)?
Which is a benefit of buying off-the-shelf systems (COTS)?
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What is a primary characteristic of structured object-oriented design processes?
What is a primary characteristic of structured object-oriented design processes?
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Which is not a common activity in object-oriented design processes?
Which is not a common activity in object-oriented design processes?
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What is the purpose of developing design models in large systems?
What is the purpose of developing design models in large systems?
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What are the tangible hardware objects in the weather station system?
What are the tangible hardware objects in the weather station system?
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Which model describes the dynamic interactions between objects in a system?
Which model describes the dynamic interactions between objects in a system?
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What do sequence models primarily represent?
What do sequence models primarily represent?
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What encapsulation construct is used in UML to show logically related groups of objects?
What encapsulation construct is used in UML to show logically related groups of objects?
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In a sequence model, how is time represented?
In a sequence model, how is time represented?
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Which type of model shows how individual objects change their state in response to events?
Which type of model shows how individual objects change their state in response to events?
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What type of model is used to show the logical grouping of objects within a system?
What type of model is used to show the logical grouping of objects within a system?
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Which of the following is NOT a model type mentioned?
Which of the following is NOT a model type mentioned?
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What is the main focus of dynamic models?
What is the main focus of dynamic models?
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What is the primary purpose of state diagrams?
What is the primary purpose of state diagrams?
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Why might you not need a state diagram for all objects in a system?
Why might you not need a state diagram for all objects in a system?
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How should object interfaces be specified?
How should object interfaces be specified?
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What is a key aspect of configuration management during software development?
What is a key aspect of configuration management during software development?
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What does the term 'host-target development' refer to?
What does the term 'host-target development' refer to?
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What major change occurred in software development practices from the 1960s to the 1990s?
What major change occurred in software development practices from the 1960s to the 1990s?
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What were common challenges faced in software development before the 1990s?
What were common challenges faced in software development before the 1990s?
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Which of the following best describes the use of UML in interface specification?
Which of the following best describes the use of UML in interface specification?
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Which statement is true regarding the reuse of software components?
Which statement is true regarding the reuse of software components?
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Study Notes
Software Design and Implementation
- Software design and implementation is the stage of software engineering where an executable software system is created.
- Design and implementation activities are often intertwined.
- Software design is a creative process. It involves identifying software components and their relationships, based on customer requirements.
- Implementation is the process of converting the design into a working program.
Build or Buy
- In many fields, ready-made systems (COTS) can be adapted to meet user needs.
- Using existing software can be faster and cheaper than developing from scratch (e.g., using pre-built medical records systems).
- When using COTS, the design process focuses on how to use the system's configuration features to achieve the desired functionality.
Object-Oriented Design Process
- Object-oriented design processes involve creating multiple system models.
- This approach requires significant effort for development and maintenance, sometimes making it cost-ineffective for smaller projects.
- For large projects with multiple teams, design models are vital for effective communication.
Process Stages
- Various object-oriented design processes exist, dependent on the organization implementing them.
- Common activities in these processes include: defining system context and usage, designing system architecture, identifying key system objects, creating design models, specifying object interfaces.
- An example illustrated is a design for a wilderness weather station.
System Context and Interactions
- Understanding the relationships between the software being designed and its external environment is critical for determining system functionality and structure.
- Defining system boundaries helps in determining the features implemented in the system and those in related systems.
Context and Interaction Models
- A system context model depicts the other systems within the environment of the system being developed (structural).
- An interaction model depicts how the system interacts with its environment during use (dynamic).
Architectural Design
- After understanding interactions with the system's environment, the system architecture can be designed.
- Major system components and their interactions are identified and organized using architectural patterns (e.g., layered or client-server).
- The weather station example consists of independent subsystems communicating over a shared infrastructure.
Object Class Identification
- Identifying object classes is a crucial but often difficult part of object-oriented design.
- No single "magic formula" exists; it relies on the experience and domain knowledge of the designers.
- This process is iterative (it takes several attempts).
Approaches to Identification
- Methods for identifying object classes include: grammatical approaches (based on natural language descriptions), domain-based approaches (focused on tangible things in the application), behavioral approaches (identifying objects based on their actions), and scenario-based approaches (identifying objects based on use cases).
Weather Station Object Classes
- Object identification in the weather station system can be based on hardware (e.g., thermometer, anemometer) and data elements (e.g., weather data).
- Application-domain objects include weather station hardware.
- The weather station's interface reflects interactions detailed in use-case models.
- Weather data encapsulates summarized data from instruments.
Design Models
- Design models illustrate objects, object classes, and relationships between them.
- Two main types of design models exist: structural models (depicting static system structure) and dynamic models (depicting dynamic interactions between objects).
Examples of Design Models
- Subsystem models represent logical groupings of objects into subsystems.
- Sequence models depict the sequence of object interactions.
- State machine models illustrate how objects change state responding to events.
- Other models exist, including use case models, aggregation models, and generalizations.
Subsystem Models
- Subsystem models illustrate how a design is structured into logically related object groups.
- UML packages represent these groupings, providing a logical model.
- Actual object organization within the system may differ.
Sequence Models
- Sequence models graphically display object interactions.
- Objects are arranged horizontally, and time flows vertically.
- Interactions occur along connected arrows.
- A thin rectangle in an object lifeline represents actions of that object.
State Diagrams
- State diagrams show how objects respond to service requests (state transitions).
- State diagrams are high-level models of system run-time behavior, not necessarily detailing all objects (many can be simple).
Interface Specification
- Object and component interfaces must be specified for parallel design.
- Interface representations should be hidden within the object itself.
- Objects may have multiple interfaces that view different aspects of their methods.
Implementation Issues
- Implementation involves more than just programming (e.g., reuse, configuration management, host-target development); these are often not included in programming texts.
- Reuse involves reusing existing components or systems in new software. Configuration Management is necessary to track changes to the software over time. Host-target development ensures software can run on different environments (eg. development vs actual server).
Reuse
- Reuse was a less significant aspect of software development from the 1960s to the 1990s. Reusing functions and programming languages libraries was a limited form of reuse. Costs and time pressure made broader software reuse less viable.
- Reuse strategies/reuse levels include: abstraction level, object level, component level, and system level.
Reuse Costs
- Reusing software includes the costs associated with search, evaluation, and adaptation.
- Adapting existing software to meet specific needs can be expensive.
- Integrating software components from different sources adds further cost, particularly for large-scale projects.
Configuration Management
- Configuration management involves tracking changes to a software system over time.
- The goal is to allow developers to access related, and changing code in a controlled manner.
- Developers need to understand the changes. A configuration management system is needed to compile and link components correctly.
Configuration Management Activities
- Version management: tracking and maintaining different versions of software components.
- System integration: specifying the components and versions used to create each system version.
- Problem tracking: managing bug reports and other issues by assigning and tracking the relevant developers and details.
Development Platform Tools
- Integrated development environments (IDEs) combine tools to support different aspects of software development.
- IDEs provide a common framework and user interface for programming tools (e.g., compilers, debugging tools, and UML model creation).
- Testing tools are useful for running predefined sets of automated tests on a program's new versions.
Open Source Development
- Open source development is based on published software source code, enabling volunteer contributions to the development process.
- The Free Software Foundation (www.fsf.org), highlights principles of open source code.
- Open source models often attract a larger volunteer community, frequently enabling faster development.
Open Source Systems
- Linux is a widely used server and desktop operating system.
- Java, the Apache web server and the mySQL database management system are also notable open-source examples.
Open Source Issues
- Organizations evaluating a product for development should consider whether or not to utilize open-source components or processes.
- Evaluating the cost-benefit of using open source software.
Open Source Business
- Business models of some organizations increasingly rely on support services for open-source software rather than selling the software itself.
- Using open-source communities may allow developing software more quickly and less expensively.
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Description
Test your knowledge on the crucial stages of software design and implementation. This quiz covers the intricacies of creating executable software systems, the build or buy decision-making process, and the object-oriented design methodology. Enhance your understanding of how software components are designed and how pre-existing systems can be adapted to meet user needs.
