1 / 9

Formal Methods in Software Engineering

Formal Methods in Software Engineering. “And they made their lives bitter with hard bondage … all their service … was with rigour.” Ex 1:14. A Spectrum of Methods. More Formal. OCL and Z. Cleanroom. Traditional Models: Waterfall, Spiral, Incremental. Agile Methods: FDD and SCRUM.

saber
Download Presentation

Formal Methods in Software Engineering

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Formal Methods in Software Engineering “And they made their lives bitter with hard bondage … all their service … was with rigour.” Ex 1:14

  2. A Spectrum of Methods More Formal OCL and Z Cleanroom Traditional Models: Waterfall, Spiral, Incremental Agile Methods: FDD and SCRUM Less Formal

  3. Characteristics of Formal Methods • Well-defined specification language • Typically based on set-theoretical concepts • Specifies by indicating operational conditions: • pre-conditions, post-conditions, and invariants • Composed of three components: • syntax, semantics, and relations (operational statements) • Emphasis on verification • Of program correctness • Of completeness of description • Of refinements to different abstractions • Testing De-emphasized

  4. Advantages of Formal Methods • Consistency (fewer contradictions) • Precision (less ambiguity) • Completeness (extent of definitions more clearly defined, so all cases handled) • Descriptive Uniformity (less mixture among levels of detail)

  5. Set Theoretical Foundation for Formal Methods • See Section 28.3 • Set Operators: , ∩, \, and x • Logic Operators: and, or, not, implication • Sequences: <a, b, c, d>, head, tail, front, last, concatenation • See Examples for Block Handler: pgs 775 and 788-790 (section 28.6.2) • OCL Notation Summary (Table28.1), pg 785 • Z Notation Summary (Table 28.2), pg 789

  6. Block Handler Example: Constraints • No block will be marked as both free and used • All the sets of blocks in the queue are subsets of currently used blocks • No elements of the queue contain the same block numbers • The collection of used and free blocks make up the total collection of all blocks • There are no duplicates among the free blocks • There are no duplicates among the used blocks

  7. OCL Example: Block Handler Free • Context BlockHandler inv: (used->intersection(free))-> isEmpty() • Context BlockHandler inv: blockQ->forAll(aBlockSet | used->includesAll(aBlockSet)) • Context BlockHandler inv: allBlocks = used->union(free) • Context BlockHandler::remove() pre: blockQ->size() > 0 post: used = used@pre – blockQ@pre->first() AND free = free@pre->union(blockQ@pre-> first()) AND blockQ = blockQ@pre-> excluding(blockQ@pre->first()) 1 3 4 6 9 Used 2 5 7 8 10 11 12 released 2 5 8 11 7 Block Queue

  8. Z Example: Block Handler Free • used, free: powerSet BLOCKS • blockQ: seq powerSet BLOCKS • used ∩ free = Ø • used U free = allBlocks • forAll i: dom blockQ : blockQ i subset used • forAll i, j: dom blockQ : i ≠ j → blockQ i ∩ blockQ j = Ø • removes(): • Pre: #blockQ > 0 • Post: used’=used–head blockQ AND free’=free U head blockQ AND blockQ’=tail blockQ 1 3 4 6 9 Used 2 5 7 8 10 11 12 released 2 5 8 11 7 Block Queue

  9. Additional Points of Emphasis • Why completeness is difficult to achieve (pg 771) • Controversy over formal methods (pg 771) • Areas in which formal methods may apply (pg 770 – “Why is it important”) • Area in which formal methods are difficult to apply (pg 792)

More Related