Shinpei Hayashi, Katsuyuki Sekine,

and Motoshi Saeki

Department of Computer Science,

Tokyo Institute of Technology, Japan

iFL: An Interactive

Environment for Understanding

Feature Implementations

ICSM 2010 ERA

14 Sep., 2010 TOKYO INSTITUTE OF TECHNOLOGY

DEPARTMENT OF COMPUTER SCIENCE

We have developed iFL− An environment for program understanding

− Interactively supports the understanding of feature

implementation using a feature location technique

− Can reduce understanding costs

Abstract

2

Program understanding is costly− Extending/fixing existing features

Understanding the implementation of target

feature is necessary

− Dominant of maintenance costs [Vestdam 04]

Our focus: feature/concept location (FL)

− Locating/extracting code fragments which

implement the given feature/concept

Background

[Vestdam 04]: “Maintaining Program Understanding – Issues, Tools, and Future Directions”,

Nordic Journal of Computing, 2004.3

FL Example (Search-based)

……

public Time(String hour, …) {

......

}

…

public void createSchedule() {

......

}

public void updateSchedule(…) {

……

scheduler

Source Code

schedule time Search

Feature Location

(Search-based approach)

FL

I want to understand

the feature

converting input time

strings to schedule

objects…

Reading these methods

for understanding 4

A new

maintainer

Constructing appropriate queries

requires rich knowledge for the

implementation − Times: time, date, hour/minute/second

− Images: image, picture, figure

Developers in practice use several

keywords for FL through trial and error

Problem 1:

How to Find Appropriate Queries?

Search

FL How??

5

Complete (Optimum) FL results are rare− Accuracy of used FL techniques

− Individual difference in appropriate code

Problem 2:

How to Fix FL Results?

schedule time Search

FL

An FL result(code fragments)

Optimum result(Code fragments that should be understood)

Unnecessary code

(false positives)

Necessary code

(false negatives)

6

Selection and understanding of code fragments

Query Input

Feature location(calculating scores)

schedule Search

1st: ScheduleManager.addSchedule()

2nd: EditSchedule.inputCheck()

…

Updating

queriesRelevance

feedback(addition of hints)

Added two feedback processes

Our Solution: Feedbacks

Finish if the user judges that he/she

has read all the necessary code fragments 7

Wide query for initial FL− By expanding queries to its synonyms

Narrow query for subsequent FLs− By using concrete identifies in source code

Query Expansion

Expand

• schedule

• agenda

• plan

schedule* date* Search

1st FL

public void createSchedule() {…String hour = …Time time = new Time(hour, …);…

}

schedule time Search

2nd FL

• list

• time

• date

A code fragment in a FL resultThesaurus

8

Dependency

Code fragmentwith its score

Improving FL results by users feedback− Adding a hint when the selected code fragments

is relevant or irrelevant to the feature

− Feedbacks are propagated into other fragments

using dependencies

Relevance Feedback

i th result of FL

1 2 9 6

: relevant

1 8 11 6

(i+1) th result of FL

propagation

by dependencies9

Supporting Tool: iFL

Implemented as an Eclipse plug-in− For static analysis: Eclipse JDT

− For dynamic analysis: Reticella [Noda 09]

− For a thesaurus: WordNet

JDT

Reticella iFL-core

Eclipse

WordNet

Exec. Traces /dependencies

Syntacticinformation

SynonymInfo.

Implemented!

10

Supporting Tool: iFL

11

How iFL Works

Inputting

Query

12

How iFL Works

Calculating

scoresEvaluated code fragments

with their scores

13

How iFL Works

Associated method will be shown

in the code editor

when user selects a code fragment

14

How iFL Works

Calculating

scores again

15

Adding

hints

How iFL Works

Scores

updated

16

How iFL Works

Codereading

FL

17

A user (familiar with Java and iFL) actually

understood feature implementations

Preliminary Evaluation

# Correct

Events

# FL

execution

Interactive

costs

Non-

interactive

costs

Δ Costs Overheads# Query

updating

S1 19 5 20 31 0.92 1 2S2 7 5 8 10 0.67 1 1S3 1 2 2 2 0.00 1 0S4 10 6 10 13 1.00 0 2S5 3 6 6 15 0.75 3 2J1 10 4 20 156 0.93 10 2J2 4 6 18 173 0.92 14 3

5 change requirements and related features

from Sched

(home-grown, small-sized)

2 change requirements and related features

from JDraw

(open-source, medium-sized)18

Evaluation Criteria

# Correct

Events

# FL

execution

Interactive

costs

Non-

interactive

costs

Δ Costs Overheads# Query

updating

S1 19 5 20 31 0.92 1 2S2 7 5 8 10 0.67 1 1S3 1 2 2 2 0.00 1 0S4 10 6 10 13 1.00 0 2S5 3 6 6 15 0.75 3 2J1 10 4 20 156 0.93 10 2J2 4 6 18 173 0.92 14 3

# selected, but unnecessary code fragments

Reduced ratio of overheads

between interactive and non-interactive approaches

19

# Correct

Events

# FL

execution

Interactive

costs

Non-

interactive

costs

Δ Costs Overheads# Query

updating

S1 19 5 20 31 0.92 1 2S2 7 5 8 10 0.67 1 1S3 1 2 2 2 0.00 1 0S4 10 6 10 13 1.00 0 2S5 3 6 6 15 0.75 3 2J1 10 4 20 156 0.93 10 2J2 4 6 18 173 0.92 14 3

Reduced costs for 6 out of 7 cases− Especially, reduced 90% of costs for 4 cases

Evaluation Results

20

# Correct

Events

# FL

execution

Interactive

costs

Non-

interactive

costs

Δ Costs Overheads# Query

updating

S1 19 5 20 31 0.92 1 2S2 7 5 8 10 0.67 1 1S3 1 2 2 2 0.00 1 0S4 10 6 10 13 1.00 0 2S5 3 6 6 15 0.75 3 2J1 10 4 20 156 0.93 10 2J2 4 6 18 173 0.92 14 3

Small overheads− Sched: 1.2, JDraw: 12 in average

Evaluation Results

21

# Correct

Events

# FL

execution

Interactive

costs

Non-

interactive

costs

Δ Costs Overheads# Query

updating

S1 19 5 20 31 0.92 1 2S2 7 5 8 10 0.67 1 1S3 1 2 2 2 0.00 1 0S4 10 6 10 13 1.00 0 2S5 3 6 6 15 0.75 3 2J1 10 4 20 156 0.93 10 2J2 4 6 18 173 0.92 14 3

No effect in S3− Because non-interactive approach is sufficient for understanding

− Not because of the fault in interactive approach

Evaluation Results

22

Summary− We developed iFL: interactively supporting the

understanding of feature implementation using FL

− iFL can reduce understanding costs in 6 out of 7

cases

Future Work− Evaluation++: on larger-scale projects

− Feedback++: for more efficient relevance feedback

• Observing code browsing activities on IDE

Conclusion

23

additional slides

Source

code

Execution trace

/ dependencies

Dynamic analysis

Methods with

their scores

Static analysis

Evaluating

eventsTestcase

Queryschedule

Based on search-based FL

Use of static + dynamic analyses

The FL Approach

Events with

their scores

(FL result)

Hints

25

Static Analysis: eval. methods

Matching queries to identifiers

public void createSchedule() {

…

String hour = …

Time time = new Time(hour, …);

…

}

20 for method names

1 for local variables

• schedule

• agenda

• time

• date

Schedule time Search

Thesaurus

The basic score (BS) of

createSchedule: 21Expand

Expanded queries26

Dynamic Analysis Extracting execution traces and their

dependencies by executing source code with

a test case

e1: loadSchedule()

e2: initWindow()

e3: createSchedule()

e4: Time()

e5: ScheduleModel()

e6: updateList()

e1

e3 e6e2

e4

e5

Dependencies

(Method invocation relations)Execution trace

27

Evaluating Methods

Highly scored events are:− executing methods having high basic scores

− Close to highly scored events

Events Methods BS Score

e1 loadSchedule() 20 52.2

e2 initWindow() 0 18.7

e3 createSchedule() 21 38.7

e4 Time() 20 66.0

e5 ScheduleModel() 31 42.6

e6 updateList() 2 19.0

e1

e3 e6e2

e4

e5

52.2(20)

18.7(0)

19.0(2)

42.6(31)

66.0(20)

38.7(21)

28

Selection and Understanding

Selecting highly ranked events− Extracting associated code fragment (method

body) and reading it to understand

public Time(String hour, …) {

…

String hour = …

String minute = … …

}

Events Methods Scores Rank

e1 loadSchedule() 52.2 2

e2 initWindow() 18.7 6

e3 createSchedule() 38.7 4

e4 Time() 66.0 1

e5 ScheduleModel() 42.6 3

e6 updateList() 19.0 5

Extracted code fragments

29

Relevance Feedback

User reads the selected code

fragments, and adds hints− Relevant (): maximum basic score

− Irrelevant to the feature (): score becomes 0

Events Methods HintsBasic

scoresScores Ranks

e1 loadSchedule() 20 52.2 77.6 2

e2 initWindow() 0 18.7 6

e3 createSchedule() 21 38.7 96.4 4 1

e4 Time() 20 46.5 66.0 70.2 1 3

e5 ScheduleModel() 31 42.6 51.0 3 4

e6 updateList() 2 19.0 530