--- title: "Why system modeling; weakness of structured analysis" subject: "Software Engineering" chapter: 2 key: "semester_5/software_engineering:system-modeling-importance" source: https://www.bctengineer.com/q/semester_5/software_engineering/system-modeling-importance site: BCT Engineering --- # Why system modeling; weakness of structured analysis Software Engineering · Chapter 2: System model - Asked in: 2068 Chaitra, 2+3 marks - Video: [Structured Analysis , process modelling , role and need of system analyst explained in hindi](https://www.youtube.com/watch?v=yuUnsuA8JK0) — Unbeaten Learning - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/software_engineering/system-modeling-importance - Whole chapter: https://www.bctengineer.com/md/semester_5/software_engineering/chapter-2 ## Question Why system modeling is important? Mention the weakness of structured analysis method? ## Short answer System modeling is important for understanding the problem, enabling communication, providing multiple perspectives, finding missing requirements, serving as design basis, and documenting the system. Structured analysis weaknesses include poor support for non-functional requirements, no suitability guidance, excessive documentation, models difficult for users, separation of data and process models, and difficulty maintaining consistency when requirements change. ## Answer **System modeling** is the process of building abstract models of a system, where each model shows the system from one perspective (context, interaction, structure or behaviour). Models are usually drawn using notations such as DFD, ER diagram, state diagram or UML. #### Why system modeling is important 1. **Understanding the problem** – a model removes unnecessary detail so the analyst can focus on the essential functions and data. 2. **Communication** – diagrams are easier for customers, analysts and developers to discuss than long text; misunderstandings are caught early. 3. **Different perspectives** – context models show the system boundary, behavioural models (DFD, state chart) show processing, and structural models (ER, class diagram) show data, so nothing important is missed. 4. **Finding missing or wrong requirements** – incomplete flows, unused data or impossible states show up in the model. 5. **Basis for design and implementation** – models evolve into architectural and detailed design; in model-driven engineering code can even be generated from them. 6. **Documentation** – models describe the existing system and the proposed system for later maintenance. #### Weaknesses of the structured analysis method Structured methods (DeMarco, Yourdon, SSADM) use DFDs, ER diagrams and data dictionaries. Their main weaknesses are: 1. **Poor support for non-functional requirements** – they model functions and data but cannot express performance, security, reliability or usability needs well. 2. **No guidance on suitability** – they do not tell the analyst whether the method suits a given kind of problem (e.g. real-time or interactive systems). 3. **Too much documentation** – they produce a large number of diagrams and dictionary entries, and the essential requirements can get hidden. 4. **Models are hard for users** – detailed, levelled models are difficult for customers to understand and validate. 5. **Separation of data and process** – functions (DFD) and data (ERD) are modelled separately, so a change in one is hard to trace to the other and the models do not map directly to object-oriented code. 6. **Difficult to maintain** – when requirements change, many levels of diagrams must be updated consistently. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is system modeling? A. Writing the final program code B. Building abstract models of a system, each showing it from one perspective C. Testing the system with real users D. Buying hardware for the system Answer: B. System modeling builds abstract models (context, interaction, structure, behaviour) that leave out unnecessary detail. (Key point: Meaning of system modeling) 2. How does modeling help find wrong or missing requirements? A. Incomplete flows, unused data or impossible states show up in the model B. It automatically rewrites the requirements C. It removes the need to talk to customers D. It guarantees that no change will ever be needed Answer: A. Gaps become visible in diagrams, such as missing inputs, unused data or impossible states. (Key point: Finding requirement errors) 3. Which is a weakness of structured analysis methods? A. They cannot model data at all B. They cannot express performance, security or usability needs well C. They only work for object-oriented programs D. They produce too few diagrams Answer: B. Structured methods model functions and data but give poor support for non-functional requirements. (Key point: Weakness: non-functional requirements) 4. Why does separating data (ERD) and process (DFD) cause problems in structured analysis? A. Changes in one model are hard to trace to the other, and they do not map directly to object-oriented code B. It makes the DFD unreadable by analysts C. The ERD cannot show entities D. It forces the use of UML Answer: A. Because functions and data are modelled separately, tracing changes between them is hard and they do not map to OO code. (Key point: Weakness: separate data and process) ## Related in other subjects - [Why risk analysis is important in planning](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Arisk-importance-analysis-planning) — Project Engineering, chapter 5 - [Challenges of modeling a physical system](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Amodeling-physical-system-challenges) — Embedded System, chapter 7 - [Structured I/O software; SCAN vs SSTF](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Astructured-io-software-scan-vs-sstf) — Operating System, chapter 6 - [Structured I/O software with diagram](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Astructured-io-software-diagram) — Operating System, chapter 6