University of Toronto Department of Computer Science University of Toronto Department of Computer Science Outline An Introduction to ‹ Why do we need Formal Methods in RE? you are here! Formal Modeling ‹ What do formal methods have to offer? ‹ A survey of existing techniques in Requirements Engineering ‹ Example modeling language: SCR ƒ The language ƒ Case study Prof Steve Easterbrook ƒ Advantages and disadvantages Dept of Computer Science, ‹ Example analysis technique: Model Checking University of Toronto, Canada ƒ How it works ƒ Case Study
[email protected] ƒ Advantages and disadvantages http://www.cs.toronto.edu/~sme ‹ Where next? © 2001, Steve Easterbrook 1 © 2000-2002, Steve Easterbrook 2 University of Toronto Department of Computer Science University of Toronto Department of Computer Science What are Formal Methods? Example formal system: Propositional Logic ‹ First Order Propositional Logic provides: ‹ Broad View (Leveson) ƒ a set of primitives for building expressions: ƒ application of discrete mathematics to software engineering variables, numeric constants, brackets ƒ involves modeling and analysis ƒ a set of logical connectives: ƒ with an underlying mathematically-precise notation and (Ÿ), or (⁄), not (ÿ), implies (Æ), logical equality (≡) ƒ the quantifiers: ‹ Narrow View (Wing) " - “for all” $ - “there exists” ƒ Use of a formal language ƒ a set of deduction rules ÿ a set of strings over some well-defined alphabet, with rules for distinguishing which strings belong to the language ‹ ƒ Formal reasoning about formulae in the language Expressions in FOPL ÿ E.g. formal proofs: use axioms and proof rules to demonstrate that some formula ƒ expressions can be true or false is in the language (x>y Ÿ y>z) Æ x>z x+1 < x-1 x=y y=x ≡ "x ($y (y=x+z)) x,y,z ((x>y y>z)) x>z) ‹ For requirements modeling… " Ÿ Æ x>3 ⁄ x<-6 ƒ A notation is formal if: ‹ Open vs.