Modelling of Complex Information Systems

IAB201
Modelling Techniques
for Information Systems
School of Information Systems
Faculty of Science
Assignment 2 Guide
Task 1 – Petri/WF-net Modelling
• Create your model step by step
– Focus on the flow of main activities (e.g. a job carried out from start to end)
– Add in other flows capturing alternative scenarios (e.g. no job / cancel job)
– Add in constraints (e.g. capacity and/or availability of resources)
– Control flow vs. resource constraints
• Pay attention to decision/choice (XOR), parallelism/concurrency
(AND), iteration/loop
– A model of only sequential flow will unlikely result in behavioural issue (from
model verification point of view)
• About making assumptions
Task 2 – Behavioural Analysis
• Construct reachability graph (using WoPeD)
– This can be generated as “Coverability Graph” of a model created in the tool
– Make sure that the graph is presented in a suitable format (e.g. tree or hierarchy) and
readable (often post-editing is necessary)
– WoPeD Tips: Always save your model in ‘Edit’ mode before switching to ‘Analyze’ mode
• Model validation
– Token game, structural correctness, occurrence sequence, or reachability analysis
• System verification
– Check behavioural correctness via reachability analysis (see next slide for details)
• Task 2 b) Your reflection on Petri net modelling task
Task 2 – Behavioural Analysis (cont’d)
Check behavioural correctness via reachability analysis
• WF-net system soundness refers to every single execution of the model, i.e., one
instance of aeromedical service.
• The number of available helicopters imposes a resource constraint to the system,
i.e., it restricts the maximum number of aeromedical service instances that can be
deployed at the same time.
• System Verification
– Approach 1: (i) Check the soundness of the WF-net system without considering the resource
constraints; (ii) Check the fact that helicopter availability impacts on the maximum number of service
instances that can run in parallel
– Approach 2: Define the notion of desired terminal markings to capture the resource capacity (e.g.,
the number of helicopters in the system) modelled in the WF-net.
WoPeD Installation
On WoPeD website, check last Q&A at https://woped.dhbw-karlsruhe.de/?page_id=275
• Q: How to fix problems with launching the WoPeD installer on Windows (error
message “This application was configured to use a bundled Java Runtime
Environment but the runtime is missing or corrupted”)?
• A: The Windows WoPeD installer consist of a JAR file wrapped into an EXE file. In order to
run this EXE, an existing Java Runtime is required with an environment variable
JAVA_HOME pointing to the folder where Java was installed. Some Java distributions (in
particular recent Oracle Java versions) do not set JAVA_HOME automatically. Lookup here
how to fix this manually.
– Click here, it will direct you to https://confluence.atlassian.com/doc/setting-the-java_homevariable-in-windows-8895.html, and then follow the instructions provided.
– The version of JAVA to install: https://www.oracle.com/java/technologies/javase-jdk16-
downloads.htm