Software Design and Implementation Overview

Design and Implementation

• Software design and implementation is an activity in software engineering where an executable software system is developed.
• Software design and implementation activities are usually interleaved.
• Software design is a creative process where software components and their relationships are identified based on customer requirements.
• Implementation is the process of creating the program based on the design.
• UML (Unified Modeling Language) is suitable when using object-oriented languages; less so with Python, and not suitable for use with configuration and COTS (Commercial Off-The-Shelf) systems.

Objectives

• The objectives are to demonstrate system modeling and architectural design in object-oriented software design.
• Understand important object-oriented design activities.
• Learn common object-oriented design models.
• Understand the concept of design patterns and their use in reusing design knowledge.
• Introduction to implementation issues like software reuse and open-source development.

Object Oriented Design

• Object-oriented systems consist of interacting objects.
• Each object maintains private local state and has operations to manipulate this state.
• Object-oriented design processes involve designing object classes and relationships between them.
• Object-oriented systems are more modifiable than those developed using functional approaches.
• Objects contain both data and operations.
• System changes to an object or adding functionalities should not affect other system objects.
• A better understanding and therefore easier maintainability of the design is achieved through a mapping between real-world entities and their objects.

Process Stages

• Diverse object-oriented design processes exist, depending on the organisation.
• System design development activities common to concepts including detailed, object-oriented design include defining system context and usage, designing system architecture, identifying key system objects, developing design models, and specifying object interfaces.

System Context and Interactions

• Understanding how a software system relates to its external environment is crucial to system functionality and structure definition.
• Defining system boundaries helps determine the implemented features, which are distinguished from other associated systems.
• Example of Context: Deciding the distribution of functionality between a control system for all weather stations versus embedded station software.

Context and Interaction Models

• System context models and interaction models provide complementary perspectives on system-environment relationships.
• A system context model is a structural representation demonstrating other systems in the environment.
• An interaction model displays how a system interacts with its environment during operation.

Weather Station Use Cases

• Weather stations interact with weather information systems to report weather data and station hardware status.
• Communication with the control system follows control commands to weather stations.

Use Case Descriptions

• Several use cases like "Report Weather," "Report Status," and "Shutdown" are described. They outline interactions between weather stations and weather information systems, including data exchange, status reporting, and shutdown procedures.

Architectural Design

• System architecture, considering major components and interactions, is designed based on system-environment understanding.
• Architectural models include common architectural patterns like layered or client-server.
• Example: Weather stations are composed of independent subsystems communicating over a shared infrastructure (communication link).

Architecture of Data Collection Subsystem

• This emphasizes components like Transmitters, Receivers, and WeatherData Objects for data collection.
• The arrangement follows a producer-consumer pattern.

Object Class Identification

• Identifying object classes is crucial in object-oriented design but complex due to a lack of straightforward methods.
• Skill, experience, and domain knowledge of the designer are key factors.
• It involves repeated reviews until accurate class identification is achieved.

Weather Station Object Classes

• Identifying objects and operations within weather station systems is aided by use-case descriptions.
• Key objects, such as those representing instruments or summaries of weather information, are identified and encapsulated in use cases.

Design Models

• Design models represent objects, object classes, and relationships.
• They highlight static system structures (structural models) in terms of object classes and interactions.
• Models also delineate dynamic object interactions like sequence and state changes.

Subsystem Models

• Visualising system structuring, organizing components into logical groups using packages, provides subsystem models.

Sequence Models

• Graphical representations illustrate object interactions in sequence models that are read top-to-bottom.
• They document interactions like service requests initiating state transitions in an object's runtime behaviors.

State Diagrams

• State diagrams showcase how system objects respond to various service requests and display transitions.

Interface Specification

• Object interfaces, for parallel component design, need specification.
• Designers should avoid interface representation, but instead focus on internal object details.

Design Patterns

• Design patterns present recurring solutions for common design problems.
• They offer a way to leverage past experience in a generalized form using object-oriented features such as inheritance and polymorphism.

The Observer Pattern

• The Observer pattern separates displays of object state from the object itself.
• This is crucial when multiple displays of an object's state are required.

Implementation Issues

• The focus shifts from programming to other crucial implementation details, like reusability and configuration management.

Reuse

• Software reusability is an approach to modern software development where significant portions of existing software are employed in new systems.
• Reusing software components and systems can accelerate development, reduce costs, and enhance reliability.
• Reuse is possible at multiple levels, from abstract design patterns to reusable objects, parts, and entire systems.

Software Reuse

• Modern software design often leverages reusable components or systems.
• Configurations are managed concerning versioning and updating through configuration management.
• Host-target development is common; software development is performed on a computer (host) different from that on which it runs. (target).

Configuration Management

• Configuration management encompasses managing software and its changes during development.
• Tools streamline the process by tracking different versions, handling updates, and enabling system integration.

Open Source Development

• Open-source software development involves publicly accessible source code, allowing community contributions.
• Licensing models grant permissions to use and adapt software, often based on the GNU General Public License (GPL) or others.

This quiz delves into the critical activities involved in software design and implementation within software engineering. It explores the relationship between design and implementation, fundamental object-oriented design concepts, and the use of design patterns. Additionally, it discusses system modeling and architectural design ideas relevant to creating effective software systems.