Lecture 28: Essentials of Structure Chart (Hierarchical System Architecture)
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Introduction to Structure Charts and Their Purpose
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Welcome, everyone! Today, we are diving into Structure Charts. These are graphical representations of how modules in a software system interrelate. Can anyone tell me why we might want to use Structure Charts in software development?
To visualize the relationships between different parts of the system?
Exactly! They help us see how the components interact, but they also define how we can organize functions systematically. This leads to clearer coding practices and easier maintenance. Now, what's the focus of Structure Charts?
I think they focus on the control hierarchy and module interfaces!
Spot on! This control hierarchy shows which modules call others and how data flows between them. Remember, the acronym **MIM**βModules, Invocation, and Modulesβcaptures the essence of what we need to focus on. What's the significance of this organization?
It helps in understanding which parts are independent and which are not?
Yes! It highlights dependencies, guiding our design choices toward low coupling and high cohesion. Summarizing our discussion, Structure Charts visualize module interaction and foster better software architecture.
Understanding Symbols and Notation in Structure Charts
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Letβs now discuss the standard symbols used in Structure Charts. Can someone describe what a module looks like in this context?
It's a rectangle, right? It represents a functional unit.
Thatβs correct! Each rectangle is labeled with a crucial verb-noun phrase to clarify its purpose, like '**Compute Tax**'. What about the lines that connect these modules?
Those are the invocation lines, and they show which module calls another.
Exactly! But there are more types, like data couples and control couples. Who can tell me their differences?
Data couples show information passed between modules, while control couples indicate flags that direct internal logic.
Well said! Hereβs a memory aid: **D**irect **C**ontrol shows flag flow β 'D' for Data, 'C' for Control. Itβs crucial to minimize control couples for cleaner designs. Can anyone think of why this is significant?
Fewer control flags lead to less coupling, making our modules easier to manage.
Absolutely! High cohesion and low coupling are the key metrics in our analyses. Thus, understanding these symbols enables us to design better software. Letβs sum up today's focus on symbols, emphasizing the make-up of each connection type.
Applying Coupling and Cohesion Principles
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Today, weβll focus on coupling and cohesion in Structure Charts. Why do you all think high cohesion within modules is essential?
Because it ensures each module has a single, clear responsibility?
Exactly, Student_4! High cohesion is vital for maintainability. Conversely, why is low coupling important?
It reduces interdependencies, so changes in one module wonβt affect others much.
Well put! Can someone explain what types of coupling are less desirable?
Control coupling is weaker because it shows modules are too dependent on each other's internal logic.
Right! The acronym **CC**: **C**ontrol is **C**lutterβnot what we want! Remember, always aim for high cohesion and low coupling. In summary, we discussed the importance of strong module identities for effective design.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
This section explores Structure Charts as essential tools in software design, detailing their notation, the importance of high cohesion and low coupling, and how to interpret and construct these charts to depict module interaction and control flow.
Detailed
Essentials of Structure Charts: A Detailed Overview
Structure Charts are vital components in the Structured Design phase, providing a graphical representation of a software system's modules and their interrelationships. They serve as a hierarchical blueprint that illustrates how functionalities are organized systematically.
Key Topics Covered:
- Purpose and Focus: Structure Charts focus on the control hierarchy, demonstrating which modules call others and the interfaces between them, making it clear how individual components interact within the system.
- Standard Symbols and Notation: Understanding the symbols used is critical for creating and interpreting Structure Charts. Key symbols include:
- Modules (Rectangles): Represent functional units. They are labeled with active verb-noun phrases indicating their purpose (e.g., "Process Order").
- Invocation Connections (Lines with Arrows): Denote which module calls another.
- Data Couples (Small Arrows with Open Circles): Indicate data flow between modules.
- Control Couples (Small Arrows with Filled Circles): Show control indicators passed between modules.
- Conditional Calls and Loops: Indicated by diamonds and arcs respectively, showing conditional and iterative execution.
- Library Modules and Off-Page Connectors: Represent reusable modules and indicate continuity of the chart on another page.
- Coupling and Cohesion: Two critical metrics for assessing module quality. High cohesion means each module performs a distinct task, while low coupling indicates minimal dependencies between modules.
- Hierarchy and Structure: Structure Charts should be logically organized, with clear readability and balance in the hierarchy to avoid confusion. The tree-like structure enables top-down understanding.
- Types of Module Connections: Sequential, conditional, and iterative executions are represented, with definitions provided for terms like fan-out and fan-in, which help understand module complexity and reusability.
- Benefits and Limitations: Structure Charts clarify system design and support parallel development; however, they also have limitations, such as not depicting internal logic or timing.
Through these concepts, students will learn how to effectively create and analyze Structure Charts to ensure well-organized, maintainable software designs.
Key Concepts
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Structure Chart: A visual blueprint of the software architecture.
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Cohesion: The importance of each module having a defined purpose.
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Coupling: Minimizing dependencies to enhance modularity.
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Invocation: Understanding how modules call one another.
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Data and Control Couples: Key connectors showing module interactions.
Examples & Applications
A banking applicationβs Structure Chart showing modules for transaction processing, account management, and reporting.
An online shopβs Structure Chart depicting product management, order processing, and customer service modules.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Cohesion high, keep modules tight, low coupling's key for future sight.
Stories
Once upon a code, a module was lost. High coupling made it hard to adjust. Cohesion held strong, it took a stand, organizing tasks across the land.
Memory Tools
Remember D.C.C: Data Couples connect, Control Couples control!
Acronyms
MIM
Modules
Invocation
Modules β to remember Structure Chart focus.
Flash Cards
Glossary
- Structure Chart
A hierarchical representation of a software system's modules and their interrelationships.
- Cohesion
The degree to which components within a module belong together, indicating a single, well-defined purpose.
- Coupling
The degree of interdependence between modules, where low coupling is preferable to minimize dependencies.
- Data Couple
An arrow representing the data passed between modules.
- Control Couple
An arrow representing a control flag passed between modules.
- Invocation
The process of a module calling upon another module to execute.
- Fanin
The number of modules calling a specific module, indicating its reusability.
- Fanout
The number of modules that a specific module calls, which can indicate complexity.
Reference links
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