The University of Melbourne
School of Computing and Information Systems SWEN90004 Modelling Complex Software Systems
Assignment 1b, 2022
Released: Monday 21 March. Deadline: 23:59, Thursday 14 April. Ob jective
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To use a higher-level modelling language to specify and reason about a concurrent system.
Background and context
Assignment 1 has two parts. The first part, 1a, was worth 10% of your final mark; this part, 1b, is worth 10%. In the first part (which you should complete before attempting this part) you designed and implemented (in Java) a concurrent simulation of tour groups visiting the Museum of Parallel Art (MoPA). Now your task is to model that system using FSP, to use LTSA to check your model, and to identify and mitigate any problems that you discover through modelling.
1. Model: The first task is to model your implementation from Assignment 1a in FSP. That is, reverse engineer an FSP model from your Java implementation. Your model should contain comments that explain the design and its components. NB: If your implementation in Assignment 1a was incomplete, or too incorrect to form the basis of an FSP model, you may wish to construct your model based on the system description in the Assignment 1a specification.
2. Check: Specify what you believe are the relevant safety and liveness properties for your FSP model. Note: for liveness, it may be the case that only a small number of properties are required. Use LTSA to check these properties.
3. Modify: You will most likely have discovered, either while completing Assignment 1a, or while completing Tasks 1 and 2 of this Assignment, that there is a potential issue with the operation of the system.)
Propose at least one modification to the design of the system that mitigates this problem and update your FSP model.
Be sure to create a copy of the file containing your original FSP model. You are re- quired to submit both the original model from Task 1 and the modified model from Task 3. If you discover any additional problems with your original Java implementation, you should also correct these in your FSP model. You may optionally also update your Java implementation to match the modified model (for practice, this is not assessed).
4. Discuss: Discuss your original and modified models. Points you may wish to address include:
• What (if any) problems did you find in your original model as a result of using LTSA?
• Were these problems also in the implementation?
• If so, why do you think you picked these up now and not before submitting As- signment 1a? What was the reasoning behind the changes you suggested in your modified model? Are there any trade-offs in system performance associated with your suggestion?
• If you did not find problems with your original implementation, were you convinced when you submitted Assignment 1a that no problems existed? Why did you believe this? Do you still believe there are no problems?
Keep your discussion to no more than 500 words
Procedure and assessment
The assignment should be completed by students individually. A late submission will attract a penalty of 1 mark for every calendar day it is late. If you have a reason that you require an extension, email Nic well before the due date to discuss this.
To tackle the assignment, first work through (and understand) the examples from lectures, and do the workshop exercises. FSP is not difficult—it is simpler than most programming languages, and much simpler than languages like Java. However, as with other languages, the way to master it is to use it, and to learn by doing. Trying to do the assignment straight up means you may struggle. Work through some easier examples first.
Submit a single zip file via the LMS. The file should include
• A file called model.lts with your initial FSP model, including the safety and liveness properties from Task 2.
• A file called model_modified.lts with your modified/corrected model, including the safety and liveness properties from Task 2.
• A plain text file called discussion.txt, containing the discussion of issues. Please ensure that this is a plain text file; ie, not a doc, docx, rtf, or other file type that requires specific software to read.
All model files and your discussion file should contain, near the top of the file, your name and student number.
We encourage the use of the subject discussion board for discussions about the project. However, all submitted work is to be your own individual work.
This project counts for 10 of the 50 marks allocated to project work in this subject. Marks will be awarded according to the following guidelines:
Clarity, abstraction
Completeness
Correctness
Formatting
Discussion Total
Description Marks
FSP models are at a suitable level of abstraction. All be- haviours relevant to interaction are specified, and there is sufficient detail to implement the system from the model. Descriptions of all actions and processes are clear and con- cise.
The model is complete. All components have been modelled and all expected behaviour is present. Suitable safety and liveness properties have been described.
The original model accurately reflects the original imple- mentation (or specification). The modified model behaves “correctly” (ie, is free of problems identified in the original model), does not violate any safety properties, and demon- strates all liveness properties.
The FSP source adheres to the code format rules from As- signment 1a where this makes sense, including the use of comments to document model components and properties. The discussion shows understanding of the subject material.
2 marks 10 marks
Why backwards?
A valid question: Why are we modelling the system after implementing it? Should it not be done the other way? Well, yes and no. Many people use modelling to understand an existing code base (just look at the number of tools for reverse engineering UML models from code bases). Reverse engineering is a great way to understand problems with an existing system. It is true, however, that in many cases, it would be cheaper and easier to do the modelling first.
The other reason why the assignment is “backwards” is that trying to model a new system using a new type of notation, such as FSP, will often end in disaster. We hope that, having gone through the Java programming stage, you feel familiar with the system to be modelled and thus can concentrate on the use of FSP. The exercise should be one of applying abstraction—a skill that is of utmost importance in any engineering discipline.
March 2022
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