Overview to System Simulation Tools

System simulation tools provide the software engineer with the ability to predict the behavior of a real-time system prior to the time that it is built. In addition, these tools enable the software engineer to develop mock-ups of the real-time system, allowing the customer to gain insight into the function, operation, and response prior to actual implementation.
Tools in this category allow a team to define the elements of a computer-based system and then execute a variety of simulations to better understand the operating characteristics and overall performance of the system. Two broad categories of system simulation tools exist :
- General purpose tools that can model virtually any computer-based system.
- Special purpose tools that are designed to address a specific application domain.

REPRESENTATIVE TOOLS :
- CSIM : Developed by Lockheed Martin Advanced Technology labs, is a general purpose discrete-event simulator for block diagram-oriented systems.
- Simics : Developed by Virtutech, is a system simulation platform that can model and analyze both hardware and software-based systems.
- SIX : Developed by Wolverine Software, provides general purpose building blocks for modeling the performance of a wide variety of systems.

Introduction to System Simulation

Systems simulation is a set of techniques for using computers to imitate, or simulate, the operations of various kinds of real-world facilities or processes.The computer is used to generate a numerical model of reality for the purposes of describing complex interaction among components of a system. The complexity of the system surges from the stochastic (probabilistic) nature of the events, from the rules for the interactions of the elements, and the difficulty to perceive the behavior of the systems as a whole with the passing of time.

When to use simulations?
Systems that change with time, such as a gas station where cars come and go (called dynamic systems) and involve randomness.Modeling complex dynamic systems theoretically need too many simplifications and the emerging models may not be therefore valid. Simulation does not require that many simplifying assumptions, making it the only tool even in absence of randomness.

System terminology:
- State: A variable characterizing an attribute in the system.
- Event: An occurrence at a point in time which may change the state of the system.
- Entity: An object that passes through the system.
- Queue: It is a task list.
- Creating: Creating is causing an arrival of a new entity to the system at some point in time.
- Scheduling: Scheduling is the act of assigning a new future event to an existing entity.
- Random variable: A random variable is a quantity that is uncertain.
- Random variate: A random variate is an artificially generated random variable.
- Distribution: A distribution is the mathematical law which governs the probabilistic features of a random variable.

Introduction to System Modeling

A model is a simplified representation of a system at some particular point in time or space intended to promote understanding of the real system. A system is understood to be an entity which maintains its existence through the interaction of its parts. A model is a simplified representation of the actual system intended to promote understanding. Whether a model is a good model or not depends on the extent to which it promotes understanding. Since all models are simplifications of reality there is always a trade-off as to what level of detail is included in the model. If too little detail is included in the model one runs the risk of missing relevant interactions and the resultant model does not promote understanding. If too much detail is included in the model the model may become overly complicated and actually preclude the development of understanding.

System modeling shows how the system should be working. To construct a system model, the system engineer should consider the following factors :
- Assumptions : It reduces the number of possible permutations and variations, thus enabling a model to reflect the problem in a reasonable manner.
- Simplifications : It enable the model to be created in a timely manner.
- Limitations : It helps to bound the system.
- Constraints : It will guide the manner in which the model is created and the approach taken when the model is implemented.
- Preferences : It indicates the preferred architecture for all data, functions, and technology. The preferred solution sometimes comes into conflict with other restraining factors.yet, customer satisfaction is often predicated on the degree to which the preferred approach is realized.

Planning Practices - Type of Software Engineering Practice

The planning activity encompasses a set of management and technical practices that enable the software team to define a road maps it travels toward its strategic goal and tactical objectives. There are many different planning philosophies. Regardless of the rigor with which planning is conducted,the following principles always apply :

- Understand the scope of the project.
- Involve the customer in the planning activity.
- Recognize that planning is iterative.
- Estimate based on what you know.
- Consider risk as you define the plan.
- Be realistic.
- Adjust granularity as you define the plan.
- Define how you intend to ensure quality.
- Describe how you intend to accommodate change.
- Track the plan frequently and make adjustments as required.

What questions must be asked and answered to develop a realistic project plan ?
- Why is the system being developed ?
- What will be done ?
- When will it be accomplished ?
- Who is responsible for a function ?
- Where are they organizationally located ?
- How will the job be done technically and managerially ?
- How much of each resource is needed ?

Communication Practices - Type of Software Engineering Practice

Before customer requirements can be analyzed, modeled, or specified they must be gathered through a communication activity. Effective communication is among the most challenging activities that confront a software engineer. However, many of the principles apply equally to all forms of communication that occur within a software project.
Software engineers communicate with many stakeholders, but customers and end users
have the most significant impact on the technical work that follows. In some cases the customer and the end user are one in the same, but for many projects, the customer and the end user are different people, working for different managers in different business organizations.

- Listen : Try to focus on the speaker's words, rather than formulating your response to those words.
- Prepare before you communicate.
- Someone should facilitate the activity.
- Face-to-face communication is best.
- Take notes and document decisions.
- Strive for collaboration.
- Stay focused, modularize your discussion.
- If something is unclear, draw a picture.
- Once you agree to something, move on.
- If you can't agree to something, move on.
- If a feature or function is unclear and cannot be clarified at the moment, move on.
- Negotiation is not a contest or a game. It works best when both parties win.

Introduction to Software Engineering Practice Cont...

Construction incorporates a coding and testing cycle in which source code for a component is generated and tested to uncover errors. Integration combines individual components and involves a series of tests that focus on overall function and local interfacing issues.
Coding principles define generic actions that should occur before code is written, while it is being created, and after it has been completed. Although there are many testing principles, only one is dominant : testing is a process of executing a program with the intent of finding an error.
During evolutionary software development, deployment happens for each software increment that is presented to the customer. Key principles for delivery consider managing customer expectations and providing the customer with appropriate support information for the software. Support demands advance preparations. Feedback allows the customer to suggest changes that have business value and provide the developer with input for the next iterative software engineering cycle.

Introduction to Software Engineering Practice

Software engineering practice encompasses concepts, principles, methods, and tools that software engineers apply throughout the software process. Every software engineering project is different, yet a set of generic principles and tasks apply to each process framework activity regardless of the project or the product.
A set of technical and management essentials are necessary if good software engineering practice is to be conducted. Technical essentials include the need to understand requirements and prototype areas of uncertainty, and the need to explicitly define software architecture and plan component integration. Management essentials include the need to define priorities and define a realistic schedule that reflects them, the need to actively manage risk, and the need to define appropriate project control measures for quality and change.
Customer communication principles focus on the need to reduce noise and improve bandwidth as the conversation between developer and customer progresses. Both parties must collaborate for the best communication to occur.
Planning principles all focus on guidelines for constructing the best map for the journey to a completed system or product. The plan may be designed solely for a single software increment, or it may be defined for the entire project. Regardless, it must address what will be done, who will do it, and when the work will be completed.
Modeling encompasses both analysis and design, describing representations of the software that progressively become more detailed. The intent of the models is to solidify understanding of the work to be done and to provide technical guidance to those who will implement the software.