Design Patterns: Observer Pattern

Design Patterns

• A pattern describes a problem with a tested solution suitable for reuse, differing from detailed specifications
• The purpose is to encapsulate design experience for reuse across different contexts
• Patterns significantly influence object-oriented software design, offering a shared vocabulary
• Applicable beyond object-oriented design, it extends to any software design, including configuration patterns
• Pattern descriptions commonly use object-oriented characteristics like inheritance and polymorphism

Pattern Elements

• Design patterns consist of four essential elements
• Name: Provides a meaningful reference to the identified pattern
• Problem Description: Explains the suitable application of the pattern
• Solution Description: Details the design solution's components, relationships, and responsibilities
• Consequences: Outlines the results and trade-offs of using the pattern

The Observer Pattern

• Name: Observer
• Description: Establishes a one-to-many dependency, where observers are automatically updated when the subject changes, decoupling the object and its display
• Problem Description: Effective when a component's state change needs to reflect to multiple components
• Solution Description: Two components
• Subject: Manages list of observers, providing methods to attach/detach
• Observers: Defines an interface for receiving updates from the subject

Observer Pattern Consequences

• Optimizations to enhance display performance are impractical
• Benefits:
• Loose Coupling: Observers are added or removed without modifying the subject
• Dynamic Updates: Real-time updates for multiple views are available
• Drawbacks:
• Performance Issues: Notification overhead may affect performance when many observers are active
• Management Complexity: Coordination of numerous observers and their lifecycles may prove challenging
• Optimization Limitations: Performance optimizations can be hindered with immediate update requirements

Design Problems and Patterns

• Observer Pattern: Informs multiple objeccts when a state of another object has changed
• Facade Pattern: Used to Streamline interfaces for related objects developed incrementally
• Iterator Pattern: Provides uniform access to a collection's elements, regardless of the internal implementation.
• Decorator Pattern: Runtime extension of class functionalities

Implementation Issues

• Extend beyond coding, encompassing reuse, configuration management, and host-target development
• Reuse: Emphasizes leveraging existing systems and components for efficiency and reduced redundancy
• Configuration Management: Involves managing software component versions, aided by a tracking system
• Host-Target Development: Requires managing software developed on one system but executed on another

Reuse in Software Development

• Evolved from 1960s where relying on reusable functions and objects within programming language libraries to today's existing software
• The focus now is on reusing existing software to improve efficiency
• Abstraction Level: Utilise knowledge to guide your software design
• Object Level: Reuse pre-existing objects from libraries
• Component Level: collections of objects and classes, known as components
• System Level: Application systems to leverage pre-built functionalities and systems

Reuse Costs

• Search and Evaluation: Encompasses time spent for finding and assessing reusable software
• Acquisition: Expenses to aquire reusable software
• Adaptation and Configuration: Costs involved in modifying reusable software to fit specific system needs
• Integration: Expenses for integrating reusable software with new code

Configuration Management

• Configuration management oversees software changes to support integration and controlled access
• Version Management: Tracks software component versions, coordinating development among programmers
• System Integration: Helps manage component versions for building system versions, enabling automatic system builds
• Problem Tracking: Allows bug reporting and tracks issue resolution

Host-Target Development

• Software is developed on a host computer but runs on target machine
• A development and an execution platform provides support software
• Key tools for the development platform include:
• Integrated Compiler and Editor: Tools to create, edit and compile code
• Language Debugging System: Tools to identify and fix debugging errors
• Graphical Editing Tools: To edit models, such as UML diagrams
• Testing Tools: Running automated tests, like JUnit
• Project Support Tools: To organize and manage code
• Development and execution platforms often differ in their installed software and architectures

Integrated Development Environments (IDEs)

• IDEs are sofware designs supporting software development within a unified framwork and user interface
• Tool Integration: IDEs streamline the development process
• Common Framework: Provides a cohesive environement where tools work together seamlessly
• Language-Specific Support: IDEs tailored to specific language , through custom development or adapting a general purpose IDE through specific tools

Component/System Deployment

• Platform Compatibility: Compatibility provides the necessary hardware and software
• High Availability: Systems deployed on multple platforms provide reduncancy
• Communication Efficiency: Minimize message delay

Open Source Development

• Is a software approach through which the source code is publicly available
• Public Access: Anyone can view, modify, and enhance
• Community Involvement: Volunteers participate in its process
• Historical Roots: The Free Software Foundation philosophy that source code should be open and not proprietary
• Internet Utilization: Recriuts a broad community of developers

Open Source Systems:

• Linux: Widely used open source operating system
• Java: Open source programming language
• Apache Web Server: Open source web server
• MySQL: Open Source Database Management System

Open Source Considerations:

• Use of Open Source Components: Whether to incoporate components into a product
• Development Approach: Evaluating methodology for software's development

Open Source Business

• Open source business model leverages open source software
• Emerging Model; Companies are adopting open source methodologies encouraging collaboration
• Revenue Focus: Companies generate revenue through offering services such as technical support, consulting, customization, and training

Open Source Community

• Cost-Effective Development: Enhancements through community without development costs
• Faster Development: Accelerates feature releases and fixes
• User Community: Encourages engagement through community

Open Source Licensing

• Open Source Licensing provides availabilty for source code and legal conditions through the developer
• Ownership and Restrictions: Licenses place conditons and restrictions
• Usage Conditions: Permits for proprietary systems
• License Models:
• GNU General Public License (GPL): Requires GPL licences to be open source
• GNU Lesser General Public License (LGPL): Allows open source code in components through licenses
• Berkeley Standard Distribution (BSD) License: Including in proprietary Software

License Management practices:

• Systematic Tracking: Maintaining open source code
• License Awareness: Understanding of licenses
• Evolution Pathways: Keeping informed of components
• Education: Education team members about practices and licensing
• Auditing: Compliance through audit systems
• Community Engagement: Participation to stay informed