1. Distributed Object-Oriented Programming with
RFID Technology
Andoni Lombide Carreton, Kevin Pinte and Wolfgang De Meuter
Department of Computer Science
Vrije Universiteit Brussel
10th IFIP International Conference on Distributed Applications and Interoperable Systems
June 7-10 2010
Amsterdam, the Netherlands 1
Monday 7 June 2010

2. Mobile RFID-enabled Applications
2
Monday 7 June 2010

3. Mobile RFID-enabled Applications
Mobile devices
2
Monday 7 June 2010

4. Mobile RFID-enabled Applications
Mobile devices
2
Monday 7 June 2010

5. Mobile RFID-enabled Applications
Mobile devices
Intermittent connectivity
2
Monday 7 June 2010

6. Mobile RFID-enabled Applications
Mobile devices
Spontaneous interactions
Intermittent connectivity
2
Monday 7 June 2010

7. Mobile RFID-enabled Applications
Scarce infrastructure
Mobile devices
Spontaneous interactions
Intermittent connectivity
2
Monday 7 June 2010

8. Mobile RFID-enabled Applications
Scarce infrastructure
Mobile devices
Representation of physical objects
Spontaneous interactions
Intermittent connectivity
2
Monday 7 June 2010

9. 5 Requirements
• Addressing physical objects (“things”)
• Storing application objects on RFID tags
• Reactivity to appearing and disappearing “things”
• Asynchronous communication with “things”
• Fault-tolerant communication
3
Monday 7 June 2010

10. 5 Requirements
• Addressing physical objects (“things”)
• Storing application objects on RFID tags
• Reactivity to appearing and disappearing “things”
• Asynchronous communication with “things”
• Fault-tolerant communication
3
Monday 7 June 2010

11. 5 Requirements
• Addressing physical objects (“things”)
• Storing application objects on RFID tags
• Reactivity to appearing and disappearing “things”
• Asynchronous communication with “things”
• Fault-tolerant communication
3
Monday 7 June 2010

12. Assumes no Non-blocking
infrastructure communication
Classless Dynamic object
object model discovery
4
Monday 7 June 2010

13. Event Loop Concurrency in AmbientTalk
5
Monday 7 June 2010

14. Event Loop Concurrency in AmbientTalk
5
Event Loop
Message queue
Monday 7 June 2010

15. Event Loop Concurrency in AmbientTalk
5
‘local’ object
Monday 7 June 2010

16. Event Loop Concurrency in AmbientTalk
5
‘remote’ object
Monday 7 June 2010

17. Event Loop Concurrency in AmbientTalk
6
Monday 7 June 2010

18. Event Loop Concurrency in AmbientTalk
6
“do m immediately”
obj.m()
obj
Monday 7 June 2010

19. Event Loop Concurrency in AmbientTalk
6
“do m eventually”
obj<-m()
Monday 7 June 2010

20. Event Loop Concurrency in AmbientTalk
6
“do m eventually”
obj<-m()
Monday 7 June 2010

21. Event Loop Concurrency in AmbientTalk
6
?
future
Monday 7 June 2010

22. Event Loop Concurrency in AmbientTalk
6
?
future
when: future becomes: { |value|
// process reply
}
Monday 7 June 2010

23. Event Loop Concurrency in AmbientTalk
6
?
future
when: future becomes: { |value|
// process reply
}
Monday 7 June 2010

24. Exporting & discovering objects
7
mplayer
Monday 7 June 2010

25. Exporting & discovering objects
7
mplayer
deftype MusicPlayer deftype MusicPlayer
Monday 7 June 2010

26. Exporting & discovering objects
7
mplayer
deftype MusicPlayer deftype MusicPlayer
export: mplayer as: MusicPlayer
Monday 7 June 2010

27. Exporting & discovering objects
7
mplayer
deftype MusicPlayer deftype MusicPlayer
export: mplayer as: MusicPlayer
whenever: MusicPlayer discovered: { |mplayer|
// open a session
}
Monday 7 June 2010

28. Exporting & discovering objects
7
mplayer
deftype MusicPlayer deftype MusicPlayer
export: mplayer as: MusicPlayer
whenever: MusicPlayer discovered: { |mplayer|
// open a session
}
Monday 7 June 2010

29. Far References
8
uploadSong
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

30. Far References
8
uploadSong
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

31. Far References
8
uploadSong
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

32. Far References
8
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

33. Far References
8
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

34. Far References
8
session
when: session<-uploadSong(s)@Due(timeout) becomes: { |ack|
// continue exchange
} catch: TimeoutException using: { |e|
// stop exchange
}
Monday 7 June 2010

35. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

36. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

37. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

38. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

39. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

40. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

41. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

42. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

43. RFID and AmbientTalk
RFID event loop
Hardware Abstraction Layer
9
Monday 7 June 2010

44. Addressing physical objects as software objects
deftype Book;
def aBook := object: {
def isbn := 123;
def title := “My book”;
def reviews := Vector.new();
RFID event loop
def setTitle(newTitle)@Mutator {
title := newTitle;
};
Hardware Abstraction Layer
def addReview(review)@Mutator {
reviews.add(review);
};
} taggedAs: Book;
10
Monday 7 June 2010

45. Addressing physical objects as software objects
deftype Book;
def aBook := object: {
def isbn := 123;
def title := “My book”;
def reviews := Vector.new();
RFID event loop
def setTitle(newTitle)@Mutator {
title := newTitle;
};
Hardware Abstraction Layer
def addReview(review)@Mutator {
reviews.add(review);
};
} taggedAs: Book;
10
Monday 7 June 2010

46. Storing objects on RFID tags
tag
aBook
RFID event loop
def aBook := object: { ... };
Hardware Abstraction Layer
when: BlankTag discovered: { |tag|
when: tag<-initialize(aBook)
becomes: { |bookReference|
// ...
}
} 11
Monday 7 June 2010

47. Storing objects on RFID tags
tag
aBook
RFID event loop
def aBook := object: { ... };
Hardware Abstraction Layer
when: BlankTag discovered: { |tag|
when: tag<-initialize(aBook)
becomes: { |bookReference|
// ...
}
} 11
Monday 7 June 2010

48. Storing objects on RFID tags
tag
aBook
RFID event loop
def aBook := object: { ... };
Hardware Abstraction Layer
when: BlankTag discovered: { |tag|
when: tag<-initialize(aBook)
becomes: { |bookReference|
// ...
}
} 11
Monday 7 June 2010

49. Storing objects on RFID tags
tag
aBook
bookRe
ference
RFID event loop
def aBook := object: { ... };
Hardware Abstraction Layer
when: BlankTag discovered: { |tag|
when: tag<-initialize(aBook)
becomes: { |bookReference|
// ...
}
} 11
Monday 7 June 2010

50. Reactivity to appearing and disappearing objects
RFID event loop
whenever: Book discovered: { |book|
// React on appearance
whenever: book disconnected: { Hardware Abstraction Layer
// React on disappearance
}
whenever: book reconnected: {
// React on reappearance
}
12
}
Monday 7 June 2010

51. Reactivity to appearing and disappearing objects
RFID event loop
whenever: Book discovered: { |book|
// React on appearance
whenever: book disconnected: { Hardware Abstraction Layer
// React on disappearance
}
whenever: book reconnected: {
// React on reappearance
}
12
}
Monday 7 June 2010

52. Reactivity to appearing and disappearing objects
RFID event loop
whenever: Book discovered: { |book|
// React on appearance
whenever: book disconnected: { Hardware Abstraction Layer
// React on disappearance
}
whenever: book reconnected: {
// React on reappearance
}
12
}
Monday 7 June 2010

53. Reactivity to appearing and disappearing objects
RFID event loop
whenever: Book discovered: { |book|
// React on appearance
whenever: book disconnected: { Hardware Abstraction Layer
// React on disappearance
}
whenever: book reconnected: {
// React on reappearance
}
12
}
Monday 7 June 2010

54. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

55. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

56. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

57. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

58. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

59. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

60. Asynchronous communication
RFID event loop
when: book<-getTitle() Hardware Abstraction Layer
becomes: { |title|
system.println(“TITLE: “ + title)
};
system.println(“Here first!”);
13
Monday 7 June 2010

61. Fault-tolerant communication
RFID event loop
def myReview := “Not for beginners”;
Hardware Abstraction Layer
when: book<-addReview(myReview)@Due(10.seconds)
becomes: { |ack|
// Message processed successfully
} catch: TimeoutException using: { |exc|
// Message timed out
} 14
Monday 7 June 2010

62. Fault-tolerant communication
RFID event loop
def myReview := “Not for beginners”;
Hardware Abstraction Layer
when: book<-addReview(myReview)@Due(10.seconds)
becomes: { |ack|
// Message processed successfully
} catch: TimeoutException using: { |exc|
// Message timed out
} 14
Monday 7 June 2010

63. Fault-tolerant communication
RFID event loop
def myReview := “Not for beginners”;
Hardware Abstraction Layer
when: book<-addReview(myReview)@Due(10.seconds)
becomes: { |ack|
// Message processed successfully
} catch: TimeoutException using: { |exc|
// Message timed out
} 14
Monday 7 June 2010

64. Addressing groups of RFID-tagged objects
def books := ambient: Book;
def computerScienceBooks := ambient: Book where: { |b|
b.category == “Computer Science”
};
def shelfFuture := computerScienceBooks<-getShelf()@Any;
when: shelfFuture becomes: { |shelf|
system.println(“Place the book in shelf: “ + shelf);
};
computerScienceBook<-setShelf(“5D”)@[ All, Sustain ]; 15
Monday 7 June 2010

65. Addressing groups of RFID-tagged objects
def books := ambient: Book;
def computerScienceBooks := ambient: Book where: { |b|
b.category == “Computer Science”
};
def shelfFuture := computerScienceBooks<-getShelf()@Any;
when: shelfFuture becomes: { |shelf|
system.println(“Place the book in shelf: “ + shelf);
};
computerScienceBook<-setShelf(“5D”)@[ All, Sustain ]; 15
Monday 7 June 2010

66. Addressing groups of RFID-tagged objects
def books := ambient: Book;
def computerScienceBooks := ambient: Book where: { |b|
b.category == “Computer Science”
};
def shelfFuture := computerScienceBooks<-getShelf()@Any;
when: shelfFuture becomes: { |shelf|
system.println(“Place the book in shelf: “ + shelf);
};
computerScienceBook<-setShelf(“5D”)@[ All, Sustain ]; 15
Monday 7 June 2010

67. Addressing groups of RFID-tagged objects
def books := ambient: Book;
def computerScienceBooks := ambient: Book where: { |b|
b.category == “Computer Science”
};
def shelfFuture := computerScienceBooks<-getShelf()@Any;
when: shelfFuture becomes: { |shelf|
system.println(“Place the book in shelf: “ + shelf);
};
computerScienceBook<-setShelf(“5D”)@[ All, Sustain ]; 15
Monday 7 June 2010

68. Addressing groups of RFID-tagged objects
def books := ambient: Book;
def computerScienceBooks := ambient: Book where: { |b|
b.category == “Computer Science”
};
def shelfFuture := computerScienceBooks<-getShelf()@Any;
when: shelfFuture becomes: { |shelf|
system.println(“Place the book in shelf: “ + shelf);
};
computerScienceBook<-setShelf(“5D”)@[ All, Sustain ]; 15
Monday 7 June 2010

69. 16
Monday 7 June 2010

70. 17
Monday 7 June 2010

71. Implementation
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

72. Implementation
Java RFID library level
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

73. Implementation
public class Transponder {
Java RFID library level }
...
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

74. Implementation
AT RFID Event Loop
Symbiosis
public class Transponder {
Java RFID library level }
...
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

75. Implementation
when: tag<-getSerial() becomes: { |nr|
AT RFID Event Loop }
...
Symbiosis
public class Transponder {
Java RFID library level }
...
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

76. Implementation
Thing level
Object serialization/backend connection
when: tag<-getSerial() becomes: { |nr|
AT RFID Event Loop }
...
Symbiosis
public class Transponder {
Java RFID library level }
...
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

77. Implementation
Thing level book<-setTitle(“Title”);
Object serialization/backend connection
when: tag<-getSerial() becomes: { |nr|
AT RFID Event Loop }
...
Symbiosis
public class Transponder {
Java RFID library level }
...
JNI
RFID hardware level
RFID Hardware Abstraction Layer
18
Monday 7 June 2010

78. Limitations and Future Work
• Processing RFID events happens sequentially within one event loop. May
lead to performance problems in very large systems?
• No data protection when multiple RFID devices write to tags concurrently.
• Efficient serialization of proxy objects is work in progress. For cheap passive
tags, we need to fit the data on ~8K of memory.
• New generation of active RFID hardware may provide solutions.
19
Monday 7 June 2010

79. Conclusion
• Represent RFID-tagged things as true mutable proxy objects in an object-
oriented system.
• Reactivity to appearing and disappearing things.
• Asynchronous and fault-tolerant communication.
• Addressing and communicating with groups of intensionally described things.
http://soft.vub.ac.be/soft/research/amopcop 20
Monday 7 June 2010