Formal specification is a technique for describing the behavior of a system in a precise and unambiguous way. This can be done using a variety of formalisms, such as mathematical logic, state machines, and Petri nets. Modeling is an important part of formal specification. It allows you to visualize the system and its components, and it helps you to understand how the system works. Modeling can also be used to verify the correctness of the system. In this summary, the following topics were summarized: - Concurrent Systems - Complex Behavior - Formal Specification through Modelling - Why Formal Specification through Modelling? -- Gain insight -- Completeness -- Correctness

1. Formal Specification
through Modeling
Summarized by Mohammed Assiri
Based on: Coloured Petri Nets: Modelling and Validation of Concurrent Systems

2. Concurrent Systems
• The vast majority of software systems today can be characterized as concurrent systems
• Structured as a collection of concurrently executing software components and applications (parallelism)
• Operation relies on communication, synchronization, and resource sharing
• It is difficult to formally specify them as the execution may proceed in many different ways depending on:
• Whether messages are lost during transmission.
• The scheduling of processes.
• The time at which input is received from the environment.
• Formal specification of concurrent systems have an astronomical number of possible executions.
• It is easy for the designer to miss important interaction patterns.
• This may lead to gaps or malfunctions in the system design.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

3. Concurrent Systems (cont.)
• Formal specification for concurrent systems are often critical.
• For many concurrent systems it is essential that they work correctly from the very
beginning:
• Nuclear power-plants.
• Aircraft control systems.
• Hospital life support equipment.
• Computer networks.
• Bank system.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

4. Complex Behavior
• The formal specification of concurrent systems is challenging due to their complex
behaviors, such as:
• Concurrently executing and independently scheduled components
• Non-deterministic and asynchronous behavior (e.g., timeouts, message loss, external events, …)
• Therefore, it is almost impossible for software developers to have a complete
understanding of the system behavior without formal specification.
• Software testing is not enough alone as it is challenging and reproducing errors is
often difficult.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

5. Formal Specification through Modelling
• One way to approach the challenge of developing concurrent systems is to
formally specify the system through modelling.
• Modelling is a universal technique that can be used across many of the activities
in system development.
• A model is an abstract representation which can be manipulated by a computer
software tool
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

6. Why Formal Specification through Modelling?
• Benefits of constructing executable models
• Insight into the design and operation of the system
• Completeness results in a more complete design
• Correctness reveals errors and ambiguities in the design phase
• Abstraction validation using high-level and domain-specific concepts in development.
• Reliability testing and verification prior to implementation and deployment
• It becomes possible to investigate how the system will behave and its existence properties.
• Functional properties (e.g., deadlocks, timing requirements,…)
• Performance properties (e.g., delay, scalability,…)
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

7. Gain insight
• Formally specifying a system through modelling and simulation usually leads to
significant new insights into the design and operation of the system.
• Formally specifying a system through modelling results in an elaborate and more
complete understanding of the system compared to reading system documents.
• The new insight can result in the following:
• A simpler and more streamlined design.
• Similarities can be identified, which can be exploited to unify and generalize the design and
make it more logical.
• We may also get ideas to improve the usability of the system.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

8. Completeness
• Formally specifying a system through an executable model usually leads to a more complete
specification of the design.
• Gaps in the specification of the system become explicit:
• They will prohibit the model from being executed because certain parts are missing.
• During simulation the designers and users will discover that certain expected events are impossible in the
current state.
• Formally specifying a system through modelling leads to a more complete identification and
understanding of the requirements to the system.
• Formally specifying a system through modelling can be used to mediate discussions among
designers and users of the system.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/

9. Correctness
• Formally specifying a system through modelling often reveals a number of design errors and
flaws.
• It is possible to control the execution of a model (unlike the real system). This means that:
• Problematic scenarios can be reproduced.
• It is possible to check whether a proposed modification of the design works as intended.
• To only simulate a number of different scenarios, without formally specifying the system, such
simulation does not necessarily lead to correct designs:
• There may be too many scenarios to investigate.
• The simulation may fail to identify some important scenarios.
• However, formal specification through modelling often decreases the number of design errors
significantly.
Summarized by Mohammed Assiri -
https://www.linkedin.com/in/mohammed-assiri/