How do we measure product and project progress?? Why is software incomparable to traditional quality of manufactured goods?

Transcription

1 Metrics How do we measure product and project progress?? 1 Why is software incomparable to traditional quality of manufactured goods? Software is intangible and has no physical presence Software is a recent thing only since the 50 s No one cares about software quality It is difficult to write complete, unambiguous specification No one has come up with software metrics yet 425/

2 Metrics What can we measure? Process Man hours Bugs reported Stories implemented Product Measures of the product are called technical metrics 425/426 3 Non-technical metrics Number of people on project Time taken, money spent Bugs found/reported By testers/developers By users Bugs fixed, features added 425/

3 Technical metrics Size of code? 425/426 5 Technical metrics Size of code Number of files Number of classes Number of processes Lines of code 425/

4 Technical metrics Size of code Number of files Number of classes Number of processes Lines of code Complexity of code? 425/426 7 Technical metrics Size of code Number of files Number of classes Number of processes Lines of code Complexity of code Dependencies / Coupling / Cohesion Depth of nesting Cyclomatic complexity 425/

5 Technical or non-technical? Number of tests Number of failing tests Number of classes in design model Number of relations per class Size of user manual Time taken by average transaction 425/426 9 Measuring size of system Function Points Lines of code (Source Lines of Code - SLOC) Number of classes, functions, files, etc. Are they repeatable? Do they work on analysis model, design model, or code? 425/

6 Function points Way of measuring functionality of system Measure of how big a system ought to be Used to predict size Several methods of computing function points, all complicated Most are proprietary 425/ Function points Count number of inputs, number of outputs, number of algorithms, number of tables in database Function points is function of above, plus fudge factor for complexity and developer expertise You need training to measure function points 425/

7 Lines of code Easy to measure All projects produce it Correlates to time to build Not a very good standard 425/ Lines of code Easy to measure All projects produce it Correlates to time to build Not a very good standard Measuring software productivity by lines of code is like measuring progress on an airplane by how much it weighs. --Bill Gates 425/

8 Lines of code copy(char *p,*q) {while(*p) *q++ = *p++;} copy(char *p,*q) { while(p) { *q++ = *p++; } } Should we include blanks? Comments? 425/ Lines of code: language matters DIGITAL-LIBRARY/Renaissance/ConsultancyReports/ D33_Planning.pdf SLOC per function point Assembly 320 C 150 Fortran 106 Pascal 91 Lisp 64 Smalltalk /

9 Lines of code: language matters Assembly code may be 2-3X longer than C code C code may be 2-3X longer than Java code Java code may be 2-3X longer than 425/ Lines of code: Validity? Lines of code is valid metric when Same language Standard formatting Code has been reviewed!! 425/

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11 Complexity Complex systems are Hard to understand Hard to change Hard to reuse Cyclomatic complexity Cohesion and coupling Software science 425/ Cyclomatic Complexity A measure of logical complexity Tells how many tests are needed to execute every statement of program Number of branches (if, while, for) /

12 Cyclomatic Complexity void processinterest() { for (acc : accounts) { if (hasinterest(acc)) { acc.balance = acc.balance + acc.balance * acc.interest } } 425/ Cyclomatic Complexity processinterest for if acc.balance =... done 425/

13 Cyclomatic complexity Number of predicates + 1 Number of edges - number of nodes + 2 Number of regions of the flow graph 425/ Testing view Cyclomatic complexity is the number of independent paths through the procedure Gives an upper bound on the number of tests necessary to execute every edge of control graph 425/

14 Metrics view McCabe found that modules with a cyclomatic complexity greater than 10 were hard to test and error prone Look for procedures with high cyclomatic complexity and rewrite them, focus testing on them, or focus reviewing on them 425/ Function points Way of measuring functionality of system Measure of how big a system ought to be Used to predict size Several methods of computing function points, all complicated Most are proprietary 425/

15 Function points Count number of inputs, number of outputs, number of algorithms, number of tables in database Function points is function of above, plus fudge factor for complexity and developer expertise You need training to measure function points 425/ One way to use metrics?? Measure the amount of code produced each month by each programmer Give high producers big raise 425/

16 Another way to use metrics Measure complexity of modules Pick the most complex and rewrite it 425/ And another way Use function points to determine how many lines of code a system will require When you write that many lines of code, stop and deliver the system 425/

17 How to use metrics Track progress Manager review Information radiator Dashboard metrics Code reviews Planning 425/ Manager review Manager periodically makes a report Growth in SLOC Bugs reported and fixed SLOC per function point (user story), SLOC per programmer (user stories per programmer) 425/

18 Information radiator Way of letting entire group know the state of the project Green/red test runner (Green/red lava lamp) Wall chart of predicted/actual stories Wall chart of predicted/actual SLOC Web page showing daily change in metrics (computed by daily build) Also see dashboard metrics 425/ Code reviews Look at metrics before a code review Coverage - untested code usually has bugs Large methods/classes Code with many reported bugs 425/

19 Planning Need to predict amount of effort Make sure you want to do it Hit delivery dates Hire enough people Predict components and SLOC Predict stories & months (XP) Opinion of developers/tech lead/manager 425/ Next time: OO metrics Reading for next time: Martin on OO Design Quality Metrics Notes on Chidamber and Kemerer s OO metrics Remember that readings are fair game for exams 425/