Workshop 1a: Software Measurement. Dietmar Pfahl

Transcription

1 Software Economics Fall 2015 Workshop 1a: Software Measurement Dietmar Pfahl (based on slides by Marlon Dumas & Anton Litvinenko)

2 Main Message Software measures can be misleading, so Either you don t use them Or you better know what they mean and how to use them.

3 Definitions: Measurement and Measure Scale & Unit Measurement: Measurement is the process through which values (e.g., numbers) are assigned to attributes of entities of the real world. Measure: A measure is the mathematical function that defines how an attribute of an entity (or rather object = instance of an entity) is mapped to a value. Source: Sandro Morasca, Software Measurement, in Handbook of Software Engineering and Knowledge Engineering - Volume 1: Fundamentals (refereed book), pp , Knowledge Systems Institute, Skokie, IL, USA, 2001, ISBN: X. MTAT / Lecture 07 / Dietmar Pfahl 2015 A Size Measure Entity: Program Attribute: Size B 4 e * 3 d * 2 c * 1 b * 0 a * LOC (lines of code) oduction/levels_of_measurement.html

4 Software Measure is a measure of anything directly related to software or its production Often, Software Metric is used as synonym for Software Measure, although metric has a specific meaning in Maths (e.g. triangle inequality) 4

5 Software Metrics in Context Software Product Size Complexity Design quality (External) product quality Software Project Quality Activity Size (effort, cost) 5

6 Lines Of Code (LOC) Product Size ???? 6

7 Lines Of Code 7

8 Lines Of Code Summary Accurate, easy to measure How to interpret... Empty lines Comments Several statements on one line Language dependent Doesn't take into account complexity Useful? 8

9 McCabe's Cyclomatic Complexity Complexity of a program Number of linearly independent paths through a function Usually calculated using the flow graph V(G) = e n + 2p e num of edges, n num of vertices, p num of connected components of the flow graph V(G) = d + 1 d num of decision (branching) points Works only for single component analysis (not several connected components; i.e. p = 1 above) 9

10 McCabe's Cyclomatic Complexity 10

11 McCabe's Cyclomatic Complexity 2: System.out.println(" "); for (Client c : clients) 4-5: System.out.println(c.getId() + " " + c.getfirstname()); e = 7 n = 6 p = 1 V(G) = 3 if (clients.size() == 0) 8: System.out.println("\tNothing"); 10: System.out.println(" "); 11

12 Cyclomatic Complexity Summary Automated (available in any modern IDE) Related to testing notions V(G) is an upper bound for the branch coverage Each control structure was evaluated both to true and false V(G) is a lower bound for the path coverage All linearly independent paths were executed Related to maintainability and defects V(G) > 10 Probability of defects rises But to be used with care: N. Nagappan, T. Ball, A. Zeller, Mining metrics to Predict Component Failures. ICSE'

13 Exercise Calculate McCabe's cyclomatic complexity of the following code snippet: 13

14 private void drawselectclientdialog() { List<Client> allclients = domaincontroller.loadallclients(); List<String> clients = new ArrayList<String>(); for (Client client: allclients) { clients.add(client.getid() + ". " + client.getfirstname()); } String selectedclient = (String)JOptionPane.showInputDialog( this, Translations.getString("main.chooseCustomer"), Translations.getString("main.chooseCustomer"), JOptionPane.OK_CANCEL_OPTION, null, clients.toarray(), 0); Client currentclient = null; try { if (selectedclient!= null) { currentclient = domaincontroller.getclientbyid( Long.parseLong(selectedClient. split(" ")[0].replaceAll("\\.",""))); } } catch(numberformatexception e) { log.error("failed to parse client id," + " probably no client was selected"); } if (currentclient!= null) { log.info("client " + currentclient.getfirstname() + " with ID=" + currentclient.getid() + " got selected."); } else { log.info("no client selected"); } model.setcurrentclient(currentclient); } MC = d + 1 = = 5 14

15 Software Metrics Software Product Size Complexity Design quality (External) product quality Software Project Quality Activity Size (effort, cost) 15

16 Coupling Coupling between object classes (CBO) Number of classes referenced by a given class (FanOut) Lack of cohesion in methods (LCOM) Number of method pairs that do not share instance variables minus number of methods that share at least one instance variable By convention, LCOM is said to be zero if the above definition gives a negative number 16

17 Coupling Example... CBO =? 17

18 Coupling Example... CBO = 1 (one other class referenced) 18

19 (Lack of) Cohesion Example LCOM = 1 2 =

20 public PersonDetails { private String _firstname; private String _surname; private String _street; private String _city; (Lack of) Cohesion Example } public PersonDetails() {} public setname(string f, String s) { _firstname = f; _surname = s; } public setaddress(string st, String c) { _street = st; _city = c; } public void printaddress() { System.out.println(_street); System.out.println(_city); } public void printname() { System.out.println(_firstname + " " + _surname); } LCOM =? 20

21 (Lack of) Cohesion Example 6 2 = 8 2 =

22 public PersonDetails { private String _firstname; private String _surname; private String _street; private String _city; (Lack of) Cohesion Example } public PersonDetails() {} public setname(string f, String s) { _firstname = f; _surname = s; } public setaddress(string st, String c) { _street = st; _city = c; } public void printaddress() { System.out.println(_street); System.out.println(_city); } public void printname() { System.out.println(_firstname + " " + _surname); } LCOM =? 22

23 Product Quality Metrics Not just about number of bugs/defects Many different models and checklists McCall's Quality Model, FRUPS, ISO 9126 Functionality, reliability, usability, portability, Cannot be measured directly must be measured via other metrics (indirect metrics) Cf. course Software Quality & Standards 23

24 Software Metrics Software Product Size Complexity Design quality (External) product quality Software Project Quality Activity Size (effort, cost) 24

25 Project Quality Metric: Defect Efficiency Ratio Efficiency of quality assurance procedures How many defects were delivered to customer DER = D before / (D before + D after ) D before defects found before delivery D after defects found after delivery What would be an ideal situation? 25

26 Observation "as the number of detected errors in a piece of software increases the probability of the existing of more undetected errors also increases" Glenford Myers, 1976 Bugs tend to cluster as you find a bug you should stop and write more tests for components where you have found a bug 28

27 Project Activity Metrics: Code Churn Amount of code changed in the software during the period of time Churned LOC number of added, modified and deleted lines of code Churn Count number of changes made to a file Files Churned number of changed files 29

28 Applications of Code Churn Metrics Overview of activity and productivity Increase in relative code churn metrics increase in defect density Number of defects per line of code Vulnerable files have higher code churn metrics Vulnerability instance of violation of the security policy Question: Is Productivity additive? (Hint: The Mythical Man Month) 30

29 Time & Effort: (Person-)Hours One (person-)hour of ideal engineering Team specific How many perfect (person-)hours in a work day? Relative measure of time and effort How many ideal engineering (person-)hours required to complete the feature Applied early Manual and subjective 31

30 Story Points Generalization of a perfect person-hour Relative measure of effort required to complete the feature Used to calculate Velocity (Productivity): Changes over time Team specific Applied early Manual and subjective 32

31 Function Points Will be covered during next week s workshop Length Size Complexity Functionality 33

32 Acknowledgments Some material inspired by or extracted from: C. Lange, Metrics in software architecting M. Gökmen, Software process and project metrics C. Martin, OO Quality design metrics E. Tempero, E. Mendes, COMPSCI 702: Software Measurement - The CK Metrics

33 Homework: Assignment 3 Details can be found here (course wiki):

34 Home Reading David Longstreet Function Point Manual 36