Part I:Introduction to Software Design
I.1 What is Design?
Design Definition:Design is the process of creating a plan or model for a potential product.It involves problem-solving and decision-making to meet specific needs and qualities.
Example:Building a house involves understanding requirements,creating a model,interacting with users for feedback,and modifying the design accordingly.
I.2 What is Software?
Software Components:Software consists of data and programs,often encapsulated as documentation,data,and programs.
Program Definition:A program is a combination of data structures and algorithms expressed in a specific programming language.
I.3 What is Software Design?
Software Design Definition:The activity of making a plan or creating a model for a software system.
Key Questions:How to create,represent,and use the plan for coding.
Design Phases:Requirements specification,abstract design,detailed design,coding.
I.4 Software Qualities
Important Qualities:Reliability,correctness,efficiency,usability,maintainability,reusability,robustness,and portability.
Examples:Reliable systems (e.g.,airplanes,sausage machines) ensure continuous,error-free operation.
I.5 Principles of Software Design
Abstraction and Decomposition:Abstraction simplifies by removing unnecessary details,while decomposition breaks down tasks into smaller components.
Encapsulation and Information Hiding:Encapsulation organizes data and operations in a unit,hiding implementation details from the outside.
Modularization:Separating functionality into independent,interchangeable modules.
I.6 Software Design Methods
Top-down Design:Starting from an abstract high-level operation and decomposing it into smaller,specific tasks.
Bottom-up Design:Building from low-level operations to construct higher-level operations and eventually the complete system.
Modular Design:Creating software systems as inter-related modules,each focusing on an independent task.
Structured Design:Combining top-down,modular,and hierarchical design for a well-organized software structure.
Object-oriented Design:Defining objects and their relationships to build the software system.
Component-based Design:Using pre-constructed software components with well-defined interfaces and functionalities.
This chapter provided us a solid foundation in understanding the concepts and processes involved in software design,emphasizing the importance of planning and creating models to ensure the development of high-quality software systems.
Part II:Structured Design and Design Representations
II.1 Dataflow Diagram (DFD)
Definition:A graphical representation focusing on data flow between operations in software.
Characteristics:It shows software design from the dataflow perspective,clearly indicates input and output for operations and suitable for abstract design.
Key Elements of DFDs:
| Key Element | Definition | Graphical Representation | Naming Rules | Use and Characteristics |
| Process (Operation) | Transformation from input to output. | Circles or rounded rectangles | Verb-object structure . Name of an organization/entity. | Synonyms:Bubble,Function,Transformation. |
| Data Flow | Movement of data from origin to destination. | Arrows indicating direction | Noun phrases indicating data type,using lowercase letters. | - |
| Data Store | Describes data at rest,such as files or databases. | Open-ended rectangles | Can use simple names or numbered references. | Connected to processes for reading or writing data. |
| Terminator | External entity interacting with the software system. | Rectangles | - | Can’t change content or behavior. Relations between terminators are not shown in the DFD. |
II.2 The Data Dictionary
What is a Data Dictionary?
A data dictionary is an organized list of definitions for all data items relevant to the program system,representing data flows and stores in DFDs.Its role is similar to an English dictionary for translating English texts into other languages.
Data Dictionary Notation
Definitions and Compositions:Data item A is defined as:A = E,where E is an expression describing the structure of A.Multiple components of a data item are listed,separated by the plus symbol(+).
Choice:Expressed with the symbol [ | ],indicating a choice among components.
Option:Expressed with round brackets (),indicating optional components (e.g.,student-name = first-name + (middle-name) + family-name).
Iteration:Represented by { },indicating zero or more occurrences of a component (e.g.,items-list = {item-d}).Limitations on iteration are expressed with specific notations,such as 1{b},{b}10,1{b}10.
Elementary Data Items:Not decomposed further and defined by their possible values.Types include natural numbers,integers,real numbers,strings,enumerations,etc.
Correctness of Data Dictionary
Must satisfy three conditions:All data items are defined;All definitions are consistent and all definitions meet data requirements.
Checks include ensuring all data flows and stores in the DFD are defined,components of composite data items are defined,no duplicate definitions,correct notation usage,and identifying any data items not in the DFD.
II.3 The Process Specification
What is Process Specification?
Problem:Processes in a DFD are not detailed,making it hard to understand the DFD accurately.
Definition:A document that specifies how a process transforms its inputs into outputs.
Processes Needing Specification
Only the lowest-level processes without decompositions in a DFD hierarchy need specification since they have no definitions.Decomposed processes in lower-level DFDs do not need specification as they are defined by their decompositions.
Notations for Process Specification
Pre- and Post-condition Notation:Pre-condition describes input constraints before execution,and post-condition describes output constraints after execution.
Structured English:A structured form of English balancing precision and readability,including basic and compound sentences.
Basic Sentences:Algebraic equations,simple imperative sentences,or a mix.
Compound Sentences:Sequences,blocks,conditionals,multiple choices,and iterations.
Decision Table:Describes actions based on combinations of conditions or values,effective for processes with complex conditions.
II.4 Control-flow Design Representations
Structure Chart
Supports top-down design,with high-level processes decomposed into collections of low-level processes they invoke.Does not show the order of invoking low-level processes and can be inconvenient for modeling complex invocations.
Jackson Structure Diagram
Used in Jackson Structured Programming (JSP),describes the sequence,selection,and iteration of procedure invocations.Basic forms include sequence,selection,and iteration constructs.
Flowchart
Graphical notation describing control flows among functions,suitable for detailed design.Hierarchical flowcharts decompose high-level functions into lower-level ones.
Nassi-Shneiderman Diagram (N-S Diagram)
Similar to flowcharts but without arrows,emphasizing structured programs with single-entry and single-exit constructs.Takes less space and ensures structured program design.
Production Rule Notation (PRN)
Textual notation for defining operations in a top-down manner,suitable for both abstract and detailed design.Can be easily transformed into programming language code,taking less space than graphical notations.
Java-based Pseudocode
Similar to Java code but allows natural language for abstraction of complex functions.Suitable for detailed design,emphasizing programming language constructs with enhanced readability
II.5 Data Structure Design
Data structure design is fundamental to programming,encapsulated by the equation:Program = Data Structure + Algorithm.
Types and Variables
Variables represent memory units with names and values.Each variable is declared with a type that defines its range of values and set of operations.
Types include basic types (e.g.,integers,real numbers,strings) and composite types (e.g.,a composite type can include multiple basic types).
Defining Types
A type is a set of values plus operations.Examples include integers (with operations like addition and subtraction) and custom types like "WeekDays" or composite types such as "Item" and "Date".
Variable Usage
Variables can be global or local.Global variables can be accessed from anywhere in the program,while local variables are confined to specific operations.
Representation of internal (temporary during execution) versus external (persistent beyond execution) data.
II.6 Modular Design
Modular design is a critical technique for creating high-quality software.It includes:
Definition of a Module:
A module is a program unit that provides functional services and can be replaced by another module with the same functionality without affecting the entire program.Modules can be functions,procedures,operations,methods,or classes.
Module Strength or Cohesion:
Measures how closely related the functions within a module are.Strong cohesion within a module implies that its components work towards a single task or closely related tasks.
Module Coupling:
Refers to the interdependence between modules.Strong coupling,often through global variables,means changes in one module can heavily affect another,while weak coupling,through parameters,enhances module independence.
Inter-module Communication:
Modules can communicate via arguments or global variables.Argument-based communication reduces coupling but may be less efficient,while global variables increase coupling but can be more efficient.
Information Hiding:
Ensures that the internal workings of a module are hidden from other modules.Only the module's interface is exposed,enhancing modularity and reducing the risk of unintended interactions.
II.7.Transformation from designs into programs
Transformation of DFDs (Data Flow Diagrams)
Transformation Strategy:Define a class for each DFD,then declare all data stores as instance variables.After that,define each process as a method within the class.Finally,implement data flow connections as method calls.
There are three types of DFD:Simple DFDs with No Stores,Complex DFDs with No Stores and DFDs with Stores.
Transformation of Hierarchical DFDs
General Strategy:Transform each DFD following previous guidelines.If a process is decomposed into a DFD,implement it by calling methods corresponding to the decomposed processes.
Transformation of Data Definitions
Elementary Data Items:Guidelines for transforming simple data types.
Composite Data Items:Strategies for transforming compositions,options,choices,and iterations of data items into classes.
Part III:Object-Oriented Design and UML (Unified Modeling Language)
III.1 Object-Oriented Design (OOD)
Definition:OOD involves creating software by defining objects and their interactions.It's contrasted with structured design,which is more function or model-oriented.
Key Concepts:
Encapsulation:Packaging data and methods within objects and restricting access to some components.
Information Hiding:Concealing internal object details and exposing only necessary parts.
Classes and Objects:Classes define the attributes and methods,while objects are instances of classes.
State Retention:Objects maintain state across method calls until they are destroyed.
Object Identity:Each object has a unique identity,often implemented as an object reference or handle.
Messages:Objects interact by sending messages to request actions or data.
III.2 UML (Unified Modeling Language)
Representation:UML is a standardized way to visualize system design.It includes notations for classes,objects,and their interactions.
Basic Notations:
Classes and Objects:Graphical representations to show attributes and methods.
Associations:Relations between classes,like inheritance,aggregation,and composition.
Inheritance:Mechanism for defining new classes based on existing ones.
Polymorphism:Ability of different classes to be treated as instances of the same class through a common interface.
Genericity:Creating classes that can operate with any data type.
Part IV:Graphical User Interface (GUI) Design
IV.1 Elements of a GUI
A GUI (Graphical User Interface) consists of various elements categorized based on their roles:
Message Elements:Provide useful information to users,like welcome messages or error notifications.
Data Elements:Allow users to input necessary information,such as text fields for names and passwords.
Functional Elements:Represent system operations,like buttons for submitting forms or menu items for saving files.
Control Elements:Enable navigation and control within the GUI,such as buttons to proceed to the next screen or to delete input.
IV.2 Principles for GUI Design
Focus on Users and Their Tasks:Prioritize user needs and tasks over the technology behind the design.This involves understanding user preferences and tasks thoroughly.
Function First,Presentation Later:Determine the necessary functions and interactions before deciding on the visual presentation.
Conform to the User's View:Design should align with how users perceive their tasks.Avoid imposing unnecessary restrictions and use user-friendly terminology.
Design for the Common Case:Features used frequently should be easily accessible and require minimal effort to use.
Facilitate Learning:Make the GUI intuitive so users can quickly learn how to use the system.Avoid ambiguities and ensure icons and text are clear.
Deliver Information,Not Just Data:Provide context and meaning along with raw data to make information useful.
Design for Responsiveness:Ensure the system provides quick feedback and appropriate messages to keep users informed about ongoing operations.
Iterate with User Feedback:Continuously test the design with users and make necessary adjustments based on their feedback.
IV.3 GUI Design Representation
GUI designs can be represented using tools like Microsoft PowerPoint for creating mockups,and Finite State Machines (FSM) for modeling the control flow between different GUI states.FSMs help define how user actions transition the interface from one state to another,ensuring clear and predictable navigation.
In essence,the principles and methods outlined help enhance the usability and effectiveness of software interfaces,ensuring they meet user needs and provide a seamless experience.
Part V:Structured Object-Oriented Formal Design (SOFD)
V.1 Introduction to SOFL
It's a method used in software engineering to ensure that the software development process is both structured and formalized.SOFL combines structured design,object-oriented design,and formal specifications to create a reliable and understandable system for software development.
V.2 SOFD (Structured Object-Oriented Formal Design)
SOFD is a methodology within SOFL that emphasizes using design functions to identify and define objects within a system.It ensures that the system's functionality is clearly defined through a formal model,making it easier to manage and verify.
V.3 Modules and Abstraction
Modules are a key concept in SOFL.They act as functional abstractions,representing behaviors with condition data flow diagrams (CDFDs).Each module defines data items and processes formally,which helps in understanding the system's function through abstraction and decomposition.Abstraction extracts the most important information while ignoring the less critical details,making complex systems easier to comprehend.
V.4 Formal Specifications
We learned about specifying functions both explicitly and implicitly.Explicit specifications detail the step-by-step process,while implicit specifications focus on the final outcome conditions.For instance,the factorial function and the Fibonacci sequence were used as examples to illustrate these specifications.
V.5 Class Structure in SOFL
In SOFL,classes and modules are structured with constants,types,variables,invariants,methods,and processes.This structured approach ensures every aspect of the system is defined and maintained consistently.
Overall,SOFL provides a comprehensive framework for developing industrial software systems.It helps in making sure the systems are not only functionally correct but also easier to verify and transform into actual programs.
Part Ⅵ:Hoare Logic for Formal Verification of Program Correctness
This last part covers the principles of Hoare Logic and its application in the formal verification of program correctness.We learned concepts such as partial and total correctness,the axioms for program proving,and the use of pre- and post-conditions (Hoare triples).
Ⅵ.1 Hoare Logic for Program Correctness
Partial Correctness:Ensures that if a precondition PPP holds before execution,the postcondition RRR will hold after execution,assuming the program terminates.
Total Correctness:Includes partial correctness and guarantees the program's termination.
Hoare Triple:Represented as {P}S{R},indicating that if P is true before executing S,R will be true after S completes.
Ⅵ.2 Program Execution and Functional Properties
The functional property of a program determines whether it performs its intended function.This can be expressed by listing initial and final states or by using pre- and post-conditions.
Ⅵ.3 Axioms for Program Proving
Assignment:x:=f
Sequence:S1;S2
Alternation:if B then S1 else S2
Iteration:while B do S
Block:begin...end
Ⅵ.4 Program Proving Techniques
Establishing necessary axioms to define the semantics of program constructs.Using formal proofs to validate Hoare triples and ensure program correctness.
Understanding and applying Hoare Logic is crucial for formally verifying the correctness of software programs.It provides a mathematical foundation to ensure programs meet their specifications and function correctly under all conditions.
二、Practical Exploration on Software Design
三、Summary
Having completed the course on Software Design,I reflect on the topics covered.The course was structured into six main sections:Introduction to Software Design,Structured Design and Design Representations,Object-Oriented Design and UML,Graphical User Interface (GUI) Design,Structured Object-Oriented Formal Design (SOFD),and Hoare Logic for Formal Verification of Program Correctness.Each of these sections provided valuable insights into different aspects of software engineering,shaping a comprehensive understanding of software design principles.
This course delved into structured design with a focus on Dataflow Diagrams (DFDs) and control-flow representations,which are crucial for creating clear,implementable designs.The course highlighted Object-Oriented Design (OOD) and the use of UML for visualizing software structures,which was both challenging and rewarding.GUI design was also emphasized,teaching us how to create intuitive and appealing user interfaces.A new concept,Structured Object-Oriented Formal Design (SOFD),combined structured and object-oriented approaches with formal specifications,ensuring reliable software development.Finally,the course covered Hoare Logic for formally verifying program correctness,which is essential for ensuring software meets its specifications.
As a student majoring in Intelligent Science and Technology,the integration of artificial intelligence and machine learning into software design processes is a trend that I am particularly interested in.These technologies have the potential to automate and enhance various design aspects,making software development more efficient and effective.
Currently AI and software are well integrated,In terms of Automated Design Assistance,AI can assist in automating repetitive design tasks.Tools like DeepCoder and Sketch2Code use AI to convert sketches or high-level descriptions into code,significantly speeding up the prototyping phase;Integrated Development Environments (IDEs) enhanced with AI can provide real-time suggestions,detect potential bugs,and even generate boilerplate code,improving productivity and code quality.
In terms of Predictive Analytics and Decision Making,By analyzing historical data and user feedback,AI can predict user behavior and preferences,guiding designers to make informed decisions.This approach ensures the software meets user needs more effectively;Machine learning algorithms can optimize various aspects of software design,such as performance tuning,resource allocation,and feature prioritization,leading to more efficient and responsive systems.
In terms of User Experience,AI algorithms can personalize the user experience by adapting interfaces and functionalities based on individual user behavior and preferences.This leads to more engaging and user-friendly software;NLP enables the creation of intuitive interfaces,such as chatbots and voice-activated assistants,which provide seamless interaction between users and software systems.
The intersection of artificial intelligence (AI),machine learning (ML),and software design is an area of immense potential and growing interest.Integrating AI and ML into software design not only enhances the capabilities of software but also transforms the design process itself,making it more efficient,adaptive,and intelligent.
In future,As AI systems become more complex,ensuring their transparency and explainability is crucial.Explainable AI techniques will help designers understand and trust AI decisions,leading to more reliable and ethical software.The development of frameworks that seamlessly integrate AI and ML capabilities into software design processes will further simplify and accelerate the creation of intelligent software and combining human creativity with AI’s analytical power can lead to innovative solutions that neither could achieve alone.Collaborative design platforms will enable this synergy,fostering creativity and innovation.
Overall,this course has provided me with a solid foundation in software design principles and techniques.Each section offered valuable insights and practical skills that I can apply in my future.I am excited to continue learning and exploring the ever-evolving field of software design.
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