Software Evolution. Software Engineering HS 16. Thomas Fritz & Martin Glinz

Transcription

1 Software Egieerig HS 16 Software Evolutio Thomas Fritz & Marti Gliz May thaks to H. Gall, K. Kevic, M. Alle, V. Razmov, M. Laza, D. Shepherd, M. Felici, G. Murphy

2 Learig Goals By the ed of this uit, you will be able to: Explai why evolutio is difficult but iheret Describe three categories of reasos why useful software must evolve ad idetify what kid of reaso motivates a give software chage Reaso about ad argue whether a give chage retais biary/cotract compatibility Describe the role of issue trackig systems i the software developmet process Discuss the life cycle of a bug report, criteria for writig a good oe ad geeral steps for workig o oe 2

3 Importace of Maiteace/Evolutio

4 Maiteace Examples Microsoft Widows XP: q Released 12/31/2001 q Service packs eded 8/30/2005 q q Support eded 4/14/2009 (7.5 years) Exteded support still possible Red Hat Eterprise Liux 3 q Released 10/23/2003 q Ed of life cycle 10/31/2010 q Ed of exteded support 01/30/2014

5 Software Maiteace/Evolutio Producig ew (versios of) software uder the costraits of existig software q Backwards compatibility is ofte assumed / required q aka Browfield developmet q Legacy Software: software which is vital to our orgaizatio, but we do t kow what to do with it (Beett ad Rajlich) Ca comprise all phases of the lifecycle, startig with requiremets gatherig q Aother tur of the spiral Similar to developmet, but HARDER!

6 Software chage Software chage is ievitable q New requiremets emerge whe the software is used q The busiess eviromet chages q Errors must be repaired q New computers ad equipmet is added to the system q The performace or reliability of the system may have to be improved A key problem for orgaisatios is implemetig ad maagig chage to their existig software systems. 6

7 Y2K Example Memory space used to be a problem, so, store 2 digit years q Rollover problem: ascedig umberig assumptio becomes ivalid Mitigatio efforts cost ~$300 billio worldwide Valuable surge i IT moderizatio q major issue for busiess: eterprise architecture Computerworld:

8 Software Evolutio Orgaizatios have huge ivestmets i their software systems - they are critical busiess assets. To maitai the value of these assets to the busiess, they must be chaged ad updated. The majority of the software budget i large compaies is devoted to evolvig existig software rather tha developig ew software. 8

9 Lehma s laws Observatios (~laws) o large systems developed by large orgaizatios Cotiuig chage A program that is used i a real-world eviromet ecessarily must chage or become progressively less useful i that eviromet Icreasig complexity As a evolvig program chages, its structure teds to become more complex. Extra resources must be devoted to preservig ad simplifyig structure. Decliig quality The quality of systems will appear to be decliig uless they are adapted to chages i their operatioal eviromet. 9

10 Evolutio is hard Systems ot robust uder chage. Lack of traceability (e.g. betwee requiremets ad code) Poor documetatio of code, of desig process ad ratioale ad of system evolutio. Stupid code features may ot be so stupid. q work-arouds of artificial costraits may o loger be documeted (e.g. OS bugs, memory limits, etc.) Poor maagemet attitudes ad culture: q q q Maiteace is ot high-profile. It is just patchig code. Easier/less importat tha desig.

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12 Discussio Questio If we build a game like Halo 5, do we ever eed to chage the applicatio s source code? Whe? Why? 12

13 Reasos for evolutioary chages Corrective q correct faults i system behaviour q caused by errors i codig, desig or requiremets Adaptive q due to chages i operatig eviromet q e.g., differet hardware or operatig system Perfective q due to chages i requiremets q ofte triggered by orgaizatioal, busiess or user learig

14 What is the reaso for this chage?

15 What is the reaso for this chage?

16 What is the reaso for this chage?

17 Evolutio ad Compatibility Cliet Applica'o 1 Cliet Applica'o 2 Applica'o Programmig Iterface (API) Applica'o A Imagie Applica'o A = Microso< Outlook What might the API provide access to? Why? Cliet Applica'o 3

18 API (Java perspective) e.g., Moyosoft Java Outlook Coector public class SedMail { public static void mai(strig[] args) { try { // Outlook applicatio Outlook outlookapplicatio = ew Outlook(); // Get the Outbox folder OutlookFolder outbox = outlookapplicatio.getdefaultfolder( FolderType.OUTBOX); // Create a ew mail i the outbox folder OutlookMail mail = (OutlookMail) outbox.createitem(itemtype.mail); // Set the subject, destiatio ad cotets of the mail mail.setsubject("hello world!"); mail.setto("your_ @test.com"); mail.setbody("this is a test message."); // Sed the mail mail.sed();

19 Evolvig a Java-based API What kid of chages to the Java API code ca we make to maitai biary compatibility so that existig (already compiled) applicatios usig the API do ot break? Add a ew (Java) package to the API? Chage ame of a public method i a public class? Chage the ame of a parameter to a method?

20 Try these oes 1. Re-order methods i a class declaratio? 2. Add a uchecked exceptio throw to a API method? 3. Chage a API method from public access to protected access? 4. Add API field? See (do t memorize these ad just uderstad the very basic kids of chages)

21 API Cotract Compatibility API chages must ot ivalidate formerly legal Cliet code. Cosider the followig API method specificatio. /** Returs the list of childre of this widget. a o-empty list of widgets */ Widget[] getchildre();

22 API Cotract Compatibility What if that specificatio was chaged i a revised API to allow a empty list of widgets to be retured? /** Returs the list of childre of this widget. a list of widgets */ Widget[] getchildre(); Would this chage break a cliet who calls getchildre()? Why or why ot?

23 API Cotract Compatibility What about this oe? /** Removes the give widgets from this widget s * list of childre. widgets a o-empty list of widgets */ void remove(widget[] widgets); chages to /** Removes the give widgets from this widget s * list of childre. widgets a list of widgets */ void remove(widget[] widgets);

24 API Cotract Compatibility.. Method pre-coditios Method post-coditios Stregthe Weake Stregthe Weake Breaks compatibility for callers Cotract compatible for callers Cotract compatible for callers Breaks compatibility for callers For more, see: This is just part of the story of cotract compatibility as the compatibility depeds o the role of the cliet code.

25 Copig with API evolutio What if you eed to upgrade part of a API ad it breaks compatibility? a) add ew API elemets alogside the old e.g., search() ad search2() b) deprecate the old versio of the API

26 What if the API is to a web service? Cliet Applica'o 1 Cliet Applica'o 2 Applica'o Programmig Iterface (API) Applica'o A A tough problem. Ca versio the URLs (REST iterface) used to access the service. Basically o great solu'o yet to my kowledge. Cliet Applica'o 3

27 Issue Trackers Are critical to teams for trackig ad maagig bugs ad feature requests Some examples Bugzilla Jazz/RTC (work items) Jira

28 Issue Trackig Systems Maage developmet requests (also called bug reports, work items, chage requests, chage tasks) q q q Defects, e.g. Usig Ctrl-+ to elarge display fails to add scroll bars whe cotet exceeds widow size Ehacemets (ew features), e.g. Add a optio to reder page immediately without waitig CSS to load boudary betwee defects ad ehacemets ca be fuzzy Maitai a list of bugs i the software q I a database called the bug repository Assig resposibility for each bug, feature, or task Orgaize the work to be doe q Life cycle of a bug report Break up the work ito releases or other deadlies

29 Issues / Bug Reports / Work Items Are ofte the major piece of iformatio i software developmet teams Cotai the ratioale for chages (provide documetatio) Cotai the liks to related documets Cotai iformatio o the people who are ivolved. 29

30 Aatomy of a bug report A bug report has the followig fields: Title (also called Summary) Descriptio Status Assigee Priority Target Milestoe Commets

31 Summary (Title) Descriptio 31

32 Filig ad triagig a bug report Who ca file a bug report? q q Ope bug repository: Ay user (usual case i OSS) Closed bug repository: Developers, Testers, QA (usual case i proprietary software) Triagig: go through a ewly filed bug report to validate ad assig the bug to a developer. q q Over the first six moths of 2010, reports were filed for Eclipse: 110 reports/day; ~5 mi per bug report: ~9 persohours/day spet o triagig Validate: cofirm it is a o-duplicate bug report; of 20K bug reports for Eclipse, 3.4K (17%) were marked ivalid, duplicate, could ot be replicated or wo t fix

33 Life Cycle of a Bug The bug report is filed UNCONFIRMED Possible resolutios: Fixed Duplicate Wo t Fix Works for Me Ivalid Owership is chaged REOPENED NEW ASSIGNED RESOLVED QA ot satisfied with solutio Developer takes possessio VERIFIED Developmet is fiished with bug QA verifies solutio worked Based o: docs/2.16/html/how.html#lifecycleimage CLOSED

34 Role of bug report commets Discussio amog reporters ad developers Might be the oly way of commuicatio for a distributed developmet team (differet locatios, time zoes) Eve whe the developers have a mea of commuicatig face-to-face, it provides a way of documetig the history of the developmet process ad the ratioale. q e.g. why it was decided to fix a bug i a certai way.

35 Summary of Bug Report Writig Guidelies (Mozilla) Be precise Be clear - explai it so others ca reproduce the bug Oe bug per report No bug is too trivial to report - small bugs may hide big bugs Clearly separate fact from speculatio Based o:

36 Guidelies cot d A good summary (title) should quickly ad uiquely idetify a bug report explai the problem, ot your suggested solutio Good: "Cacellig a File Copy dialog crashes File Maager Bad: "Software crashes Bad: "Browser should work with my web site A good descriptio should iclude Provide eough cotext Overview, steps to reproduce, actual results, expected results Survey study foud most helpful iformatio to be:steps to reproduce, stack traces, test cases T.Zimmerma et al., What makes a good bug report, IEEE Trasactios o Software Egieerig, vol. 36, No. 5, Sep./Oct. 2010

37 Oe bug

38 May bugs

39 May issues/bugs

40 Questio: How do you perform a chage task? Summary: Applicatio crash o clickig the SAVE butto while creatig a ew user. Descriptio: Applicatio crash o clickig the SAVE butto while creatig a ew user, hece uable to create a ew user i the applicatio Steps to reproduce: 1) Logo ito the applicatio 2) Navigate to the Users Meu > New User 3) Filled all the user iformatio fields 4) Clicked o Save Butto 5) See a error page ORA1090 Exceptio: Isert values Error 6) See attached logs for more iformatio ad also attached screeshot 40

41 Time sped durig chage tasks Adrew J. Ko, Htet Aug, ad Brad A. Myers. Elicitig desig requiremets for maiteace-orieted ides: a detailed study of corrective ad perfective maiteace tasks. ICSE

42 Workig o a chage task search " terms" code search" avigatio" chage task" (Jira/Bugzilla/...)" Itegrated Developmet Eviromet (IDE)" evetually editig

43 Workig o a chage task Problems/Difficulties: Too much code to uderstad/read all Laguage mismatch: bug reports (NL) source code Crosscuttig cocers: code is ofte tagled ad scattered To localize ad edit relevat code Idetify good search terms Take advatage of tool support, e.g. code search, structural avigatio support, breakpoits (debuggig) Take advatage of iformatio provided i bug reports, such as stack traces, ad also o ews forums, such as stackoverflow 43

44 Summary Evolutio is tough but a iheret ad importat part of software developmet Evolutioary chages ca be corrective, adaptive ad perfective API cotract compatibility esures that cliet code still rus as expected after API evolves Issue Trackig Systems are a itegral part of most software developmet ad writig good bug reports is importat Much time o a chage task is sped avigatig ad searchig

45 Evolutio i actio

46 What kid of task? Corrective / adaptive / perfective 46

47 Evolutio i actio 1. Dowload jhotdraw from ifi.uzh.ch/seal/people/kevic/tools/jhotdraw_labstudy_2.zip 2. Ope Eclipse 3. Import JHotDraw Package Explorer > Import > Projects from Folder or Archive > Archive 4. Ru JHotDraw 1. Ru As > Java Applicatio 2. Select Mai class org.jhotdraw.samples.draw 47

48 Fix the bug: first steps? 48