Explain What is Iterative & Evolutionary System Sequence Diagram (SSD) in Details

System Sequence Diagram (SSD) is a graphical representation of the interactions between actors and the system under consideration. It is one of the most fundamental diagrams in the Unified Modeling Language (UML) and is used to capture high-level requirements and design of a system. SSDs are an essential part of the requirements analysis phase and are used to capture use cases and user stories. In this article, we will explore two types of SSDs, Iterative SSDs and Evolutionary SSDs, their advantages, disadvantages, and differences.

Types of SSDs

A. Iterative SSDs 

Iterative SSDs are used to model systems that undergo frequent and incremental changes. These changes are usually driven by user feedback, changing requirements, and market needs.

Iterative SSDs are used to capture the interactions between actors and the system at different stages of the development cycle. These interactions are usually represented as a sequence of messages exchanged between the actor and the system.

Advantages of Iterative SSDs

The advantages of using Iterative SSDs are as follows:

1. They provide a clear and concise representation of the system's interactions with its users.
2. They can be easily updated and modified to reflect changes in the system's requirements.
3. They facilitate communication between stakeholders and help to identify potential design flaws early in the development cycle.
4. They are an effective tool for managing project scope and prioritizing development tasks.
5. They can be used to identify and prioritize test cases and scenarios.

Disadvantages of Iterative SSDs

The disadvantages of using Iterative SSDs are as follows:

1. They can become complex and difficult to manage when the system undergoes multiple iterations.
2. They may not provide a complete picture of the system's behavior, as they only capture a subset of the system's interactions with its users.
3. They require a high level of collaboration between stakeholders, which can be difficult to achieve in large projects.
4. They may not be suitable for systems that require a high degree of precision or formal verification.

B. Evolutionary SSDs 

Evolutionary SSDs are used to model systems that undergo gradual and continuous changes. These changes are usually driven by the system's ability to adapt to changing environments, user needs, and emerging technologies.

Evolutionary SSDs are used to capture the system's interactions with its users over time. These interactions are usually represented as a series of snapshots, each capturing the system's behavior at a particular point in time.

Advantages of Evolutionary SSDs

The advantages of using Evolutionary SSDs are as follows:

1. They provide a historical record of the system's interactions with its users, allowing developers to trace the evolution of the system's requirements and design over time.
2. They facilitate communication between stakeholders by providing a shared understanding of the system's behavior and evolution.
3. They are an effective tool for managing the system's long-term evolution and ensuring its continued relevance and usefulness.
4. They can be used to identify and prioritize maintenance and upgrade tasks.

Disadvantages of Evolutionary SSDs

The disadvantages of using Evolutionary SSDs are as follows:

1. They can become complex and difficult to manage when the system undergoes significant changes or when the number of snapshots becomes too large.
2. They may not provide a complete picture of the system's behavior, as they only capture a subset of the system's interactions with its users.
3. They require a high level of collaboration between stakeholders, which can be difficult to achieve in large projects.
4. They may not be suitable for systems that require a high degree of precision or formal verification.

Comparison between Iterative SSDs and Evolutionary SSDs

The following table summarizes the differences between Iterative SSDs and Evolutionary SSDs:

Feature	Iterative SSDs	Evolutionary SSDs
Development Approach	Incremental	Continuous
System Changes	Frequent and incremental	Gradual and slow
Representation	Sequence of interactions	Series of snapshots
Focus	Short-term development	Long-term evolution
Advantages	Easy to update	Historical record
	Prioritize development	Identify maintenance tasks
	Identify test cases	Facilitate communication between stakeholders
Disadvantages	Can become complex	Can become complex
	May not provide complete	May not provide complete
	Requires high	Requires high
	level of collaboration	level of collaboration
	May not be suitable for	May not be suitable for
	systems requiring	systems requiring
	precision or formal	precision or formal
	verification	verification

Iterative SSDs are designed to model systems that undergo frequent and incremental changes. The development approach is incremental, which means that the system changes frequently and in small increments. The representation of the system's behavior is a sequence of interactions, which captures the system's behavior at different stages of the development cycle. Iterative SSDs focus on short-term development and are useful for prioritizing development tasks, identifying test cases, and managing project scope.

Evolutionary SSDs, on the other hand, are designed to model systems that undergo gradual and continuous changes. The development approach is continuous, which means that the system changes gradually over time. The representation of the system's behavior is a series of snapshots, which captures the system's behavior at different points in time. Evolutionary SSDs focus on the long-term evolution of the system and are useful for identifying maintenance and upgrade tasks, facilitating communication between stakeholders, and ensuring the system's continued relevance and usefulness.

Both Iterative SSDs and Evolutionary SSDs have their advantages and disadvantages. Iterative SSDs are easy to update, prioritize development tasks, and identify test cases. However, they can become complex, may not provide a complete picture of the system's behavior, and require a high level of collaboration between stakeholders. Evolutionary SSDs provide a historical record of the system's behavior, facilitate communication between stakeholders, and identify maintenance tasks. However, they can also become complex, may not provide a complete picture of the system's behavior, and require a high level of collaboration between stakeholders.

Conclusion

System Sequence Diagrams (SSDs) are essential tools for capturing high-level requirements and design of a system. There are two types of SSDs, Iterative SSDs, and Evolutionary SSDs. Iterative SSDs are designed to model systems that undergo frequent and incremental changes, while Evolutionary SSDs are designed to model systems that undergo gradual and continuous changes. Both types of SSDs have their advantages and disadvantages, and the choice of which one to use depends on the nature of the system being modeled and the project's goals.