Formal specification facts for kids

Formal specifications are special ways to describe how computer systems and software should work. They use ideas from mathematics to be very clear and exact. Think of them as a super detailed blueprint for a computer program.

These specifications help people:

• Understand what a system needs to do.
• Check if the system will behave correctly.
• Design the system in a way that avoids mistakes.

They are called formal because they follow strict rules, like a special language. This helps computer scientists make sure everything is just right.

Why We Need Them

Computers and software are becoming more and more important in our lives. They control everything from our phones to power grids. Because of this, it's super important that they work perfectly and don't have errors.

Engineers who build bridges or airplanes use math to make sure their designs are safe. Formal specifications do something similar for software. They help make sure computer programs are reliable and do what they are supposed to do. Other ways, like testing software, are also used to make programs better.

How They Are Used

Once you have a formal specification, you can use special methods called formal verification. These methods help you prove that a computer system's design is correct. It's like checking your math homework step-by-step to be sure you got the right answer.

This is very helpful because it lets people find and fix mistakes in a design before they spend a lot of time and money building the actual software. It's much cheaper to fix a mistake on paper than after you've already built the whole thing!

Another way is to build the software step-by-step, making sure each step is correct. This way, the final program is "correct by design."

It's important to remember that a formal specification is not the actual computer program. Instead, it's a guide that explains what the program should do, not how it should do it.

A good specification should be:

• Clear and easy to understand.
• Consistent (doesn't contradict itself).
• Complete (covers everything needed).
• Easy to build from and change later.
• Useful for checking the program's behavior.

One main reason for using formal specifications is that they allow computer scientists to prove things about software. These proofs can show that a design is correct or that a program works as expected.

Things to Consider

Even though formal specifications are powerful, they have some challenges:

• Not always "perfect": A design can only be correct if it matches its specification. But what if the specification itself doesn't perfectly describe the real-world problem? It's hard to formally prove that the specification itself is exactly right.
• Not widely used: Many companies don't use formal methods for all their software. This is because:

* Time: They can take a lot of time and effort to create at the beginning of a project. * Flexibility: Some software teams use agile methods that focus on changing things quickly. Formal specifications can seem less flexible. * Complexity: They often need people with strong math skills to understand and use them. * Cost: Companies sometimes think they are too expensive. However, for very important systems (like those in airplanes or medical devices), they can actually save money by preventing costly errors.

• Limited scope: They might not cover everything that everyone involved in a project cares about. For example, they aren't great at describing how a user interface (what you see on the screen) should look or feel.

Different Types of Specifications

Formal specifications have been used in different ways for a long time. The way they are built can depend on the type of system they are describing. Here are some common types:

• History-based specification: Focuses on how a system behaves over time.
• State-based specification: Looks at the different "states" a system can be in. For example, how a financial transaction moves from "pending" to "completed." Languages like Z and VDM use this.
• Transition-based specification: Describes how a system moves from one state to another. This is good for systems that react to things, like a traffic light changing colors.
• Functional specification: Describes a system using mathematical functions.
• Operational specification: Focuses on how a system works step-by-step.

Tools for Formal Specifications

There are special languages and tools that help people create and work with formal specifications.

Some well-known specification languages include:

• Z
• Specification Language (VDM-SL) from the Vienna Development Method
• Abstract Machine Notation (AMN) from the B-Method

Some tools that help with formal specifications are:

• Algebraic tools:

* Larch * OBJ * Lotos

• Model-based tools:

* Z * B * VDM * CSP * Petri Nets * TLA+

See also

In Spanish: Especificación formal para niños

• Algebraic specification
• Formal methods
• Model-based specification
• Software engineering
• Specification language
• Specification (technical standard)