Tracking Objects to Detect
Feature Dependencies
Adrian Lienhard, Orla Greevy and Oscar Nierstrasz
Software Composition Group
University of Bern, Switzerland

Context
“A feature is an observable unit of behavior of a system
triggered by the user” [Eisenbarth’03]
Example: IRC client
Open, Setup, Connect, Join Channel,
Send Message, Receive Message, Disconnect
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

No feature is an island
We consider a runtime dependency to exist
between features if state-changes in one feature
impact the behavior of another feature.
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Why object aliasing
causes dependencies
Open Join Channel Receive Message
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Why object aliasing
causes dependencies
Open Join Channel Receive Message
window
connection
Snapshot 1
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Why object aliasing
causes dependencies
Open Join Channel Receive Message
window window
connection connection
channel
Snapshot 1 Snapshot 2
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Why object aliasing
causes dependencies
Open Join Channel Receive Message
window window
connection connection
channel
Snapshot 1 Snapshot 2
...
conn := channel.getConnection();
conn.nextMessage();
...
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Open Join Channel Receive Message
window window
connection connection
Snapshot
view
channel
Snapshot 1 Snapshot 2
Identify the creation of all references of an object
and how they are transferred
Open Join Channel Receive Message
Object
flow view
of connection
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Open Join Channel Receive Message
window window
connection connection
Snapshot
view
channel
Snapshot 1 Snapshot 2
Identify the creation of all references of an object
and how they are transferred
Open Join Channel Receive Message
Object
flow view <new> model
of connection
reference returned
store into field (of
from instantiating
window instance)
the connection
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Open Join Channel Receive Message
window window
connection connection
Snapshot
view
channel
Snapshot 1 Snapshot 2
Identify the creation of all references of an object
and how they are transferred
Open Join Channel Receive Message
Object
flow view <new> model model connection
of connection
store into field (of
read from field
channel instance)
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Open Join Channel Receive Message
window window
connection connection
Snapshot
view
channel
Snapshot 1 Snapshot 2
Identify the creation of all references of an object
and how they are transferred
Open Join Channel Receive Message
Object
flow view <new> model model connection connection conn
of connection
stored into local
read from field variable -- then
used as target of
message send
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Detecting dependencies
‣ Identify the reference through which a message is sent
to its target
‣ From this reference, follow the object flow backwards
‣ If a previous reference originates in different feature,
we found a dependency
Open Join Channel Receive Message
<new> model model connection connection conn
➾ the connection instance causes two
dependencies for the Receive Message feature
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Exploring dependencies
Object dependency graph of Receive Message
‣ nodes: objects
depended on
‣ edges: references
subject to a
dependency
Open Join Channel
Connect Send Message
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Exploring dependencies
Object dependency graph of Receive Message
‣ nodes: objects
depended on
‣ edges: references
subject to a
dependency
Open Join Channel
Connect Send Message
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Exploring dependencies
Object dependency graph of Receive Message
‣ nodes: objects
depended on
‣ edges: references
subject to a
dependency
Open Join Channel
Connect Send Message
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Exploring dependencies
Object dependency graph of Receive Message
‣ nodes: objects
depended on
‣ edges: references
subject to a
dependency
Open Join Channel
Connect Send Message
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

IRC client dependencies
Open
Setup
Connect
MOTD
Join Channel
Send Message
Receive Message
New Console
Disconnect
0 5 10 15 20 25 30 35
Our approach Salah et al.
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Pier CMS dependencies
Initialization
Start
Login
Add Page
Copy Page
Edit Page
Change Group
Change Other
Change Owner
Remove Page
Logout
0 100 200 300 400
Our approach Salah et al.
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch

Conclusions
‣ Analyzing where objects are created does not
reveal dependencies caused by object aliasing
‣ By tracking the flow of objects we can
accurately detect feature runtime dependencies
ICPC’07 : : Tracking Objects to Detect Feature Dependencies : : Adrian Lienhard : : lienhard@iam.unibe.ch