This document discusses building a software ecosystem for Java-Prolog interoperability. It introduces JPC, a portable Java library for Java-Prolog connectivity that facilitates object-to-term mappings. It also introduces LogicObjects, a Java-Prolog linguistic symbiosis framework built on JPC that uses annotations to specify mappings. The document then presents a case study of modeling the London underground in Prolog with a Java interface using these libraries to achieve linguistic symbiosis between the languages.

1. Towards a Software Ecosystem
for Java-Prolog Interoperability
Sergio Castro Kim Mens
RELEASeD LAB
Université catholique de Louvain
Belgium
Paulo Moura
Center for Research in Advanced Computing Systems
INESC TEC
Portugal
1
Tuesday 9 July 13

2. 2
LogicObjects
Future work/
Conclusions
Content
JPC
Hydra
(or how to build reusable hybrid components)
Tuesday 9 July 13

3. 2
LogicObjects
Future work/
Conclusions
Content
JPC
Hydra
(or how to build reusable hybrid components)
Tuesday 9 July 13

4. 2
LogicObjects
Future work/
Conclusions
Content
JPC
Hydra
(or how to build reusable hybrid components)
Tuesday 9 July 13

5. 2
LogicObjects
Future work/
Conclusions
Content
JPC
Hydra
(or how to build reusable hybrid components)
Tuesday 9 July 13

6. 3
OO
programming
Logic
programming
Appropriate for modelling
real-world concepts
Often enjoy rich software
ecosystems
Declarative reasoning
Tuesday 9 July 13

7. 3
OO
programming
Logic
programming
Appropriate for modelling
real-world concepts
Often enjoy rich software
ecosystems
Declarative reasoning
Tuesday 9 July 13

8. 3
OO
programming
Logic
programming
Appropriate for modelling
real-world concepts
Often enjoy rich software
ecosystems
Declarative reasoning
Tuesday 9 July 13

9. 3
OO
programming
Logic
programming
Appropriate for modelling
real-world concepts
Often enjoy rich software
ecosystems
Declarative reasoning
Tuesday 9 July 13

10. Integration difficult to achieve
• The Prolog community is fragmented.
• Existing Java-Prolog libraries also suffer the symptoms of such
fragmentation.
4
Tuesday 9 July 13

11. An ecosystem for Java-Prolog
development
• Providing a portable general-purpose library for building Java-
Prolog systems (JPC).
• Providing a framework for linguistic symbiosis between Java &
Prolog (LogicObjects).
• Providing a set of reusable hybrid components.
5
Tuesday 9 July 13

12. Why Java ?
• None of the authors is a big fan of the Java language itself.
• But we recognise the advantages of the huge Java ecosystem.
• And the emerging languages running on the JVM
• (e.g., Scala, Clojure, JRuby, etc...).
6
Tuesday 9 July 13

13. • Facilitates the creation of hybrid Java-Prolog applications and
frameworks.
• Not constrained to a specific execution environment (e.g. an
Eclipse plugin).
• Compatible with some of the most popular open source
Prolog engines (XSB,YAP, SWI) and more coming soon.
• Available at the Maven central snapshot repository and
GitHub1 (currently) under the LGPL license.
7
1https://github.com/sergio-castro/
JPC: Java-Prolog Connectivity
Tuesday 9 July 13

14. Lessons learned when building
libraries without JPC
• Applications are strongly coupled to a concrete Java-Prolog
library.
• Conversion concerns tangled with other concerns.
• Complex routines dealing with conversion heuristics (high
cyclomatic complexity).
• Ugly ad-hoc implementation of context-dependent
conversions.
8
Tuesday 9 July 13

15. JPC features
• A portable abstraction of a Prolog virtual machine.
• A set of utilities for dealing with Java-Prolog inter-language
conversions.
9
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16. JPC as a portable layer
10
Prolog engines
Bridge libraries
JPC drivers
JPC library
Java-Prolog
applications
Java-Prolog
frameworks
(layer coupling denoted by the
direction of the arrows)
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17. 11
A Prolog query
browser based on
JPC
Tuesday 9 July 13

18. 12
Tuesday 9 July 13

19. JPC as a tool for inter-language
conversions
• JPC implements a “new” mechanism for passing artefacts
between Java and Prolog.
• Mechanism based on the specification of mappings of such
artefacts.
13
Tuesday 9 July 13

20. Common integration techniques
• Shared memory approach (e.g. SOUL).
• Passing object references to Prolog (e.g. JPL).
• Serializing objects (e.g. InterProlog).
• Mapping objects to terms (e.g. JPC, LogicObjects).
14
Tuesday 9 July 13

21. Shared memory approach
• Tight integration/control between Java and Prolog.
• Difficult to implement an efficient Prolog embedded in Java.
• Often no access to well-proven Prolog libraries.
• But easy access to libraries in the host language.
15
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22. Passing object references
• The original object reference is preserved.
• Garbage collection may be an issue.
• No control on the term representation of an object on the
Prolog side.
16
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23. Serializing objects
• Object reference is not preserved.
• No configuration required.
• Only works with serializable objects.
• Support for circular relations.
• No control on the term representation of an object on the
Prolog side.
17
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24. Mapping objects to terms
• Object reference is difficult to preserve.
• Difficult to support circular relations.
• Requires explicit mappings (where they cannot be inferred).
• Fine control on the (context dependent) term representation
of an object.
18
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25. JPC mapping features
• Helps to modularize context dependent conversions.
• Converters can receive hints on the expected conversion to
apply.
• Custom conversions can be added at any moment.
• Catalog of useful Prolog-Java converters.
19
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26. JPC architecture
• Abstraction of a PrologVM.
• Reification of Prolog data types (e.g.Atom, Compound, etc).
• The conversion context.
20
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27. Conversion context components
• The converter manager.
• The type solver.
• The instantiation manager.
21
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28. The converter manager
• Converts between Java-Prolog artefacts.
• Composition of specialized converters (primitive types
converters, exception converters, multi-valued converters,
etc).
• Interprets and refines hints from the user.
22
Tuesday 9 July 13

29. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
Tuesday 9 July 13

30. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
Java type
Tuesday 9 July 13

31. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
Prolog type
Tuesday 9 July 13

32. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
term to convert
Tuesday 9 July 13

33. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
type guiding conversion
Tuesday 9 July 13

34. public class CollectionConverter<E> extends JpcConverter<Collection<E>, Term> {
@Override
public Collection<E> fromTerm(Term listTerm, Type type, Jpc context) {
...
}
...
}
23
A pre-defined converter example
the conversion context
Tuesday 9 July 13

35. A default conversion example
Jpc jpc = ... //the conversion context
Term listTerm = listTerm(new Atom("1"), new Atom("2")); //[‘1’, ‘2’]
List<String> list = jpc.fromTerm(listTerm);
assertEquals("1", list.get(0));
assertEquals("2", list.get(1));
24
Tuesday 9 July 13

36. A default conversion example
Jpc jpc = ... //the conversion context
Term listTerm = listTerm(new Atom("1"), new Atom("2")); //[‘1’, ‘2’]
List<String> list = jpc.fromTerm(listTerm);
assertEquals("1", list.get(0));
assertEquals("2", list.get(1));
24
Prolog list of
atoms
Tuesday 9 July 13

37. A default conversion example
Jpc jpc = ... //the conversion context
Term listTerm = listTerm(new Atom("1"), new Atom("2")); //[‘1’, ‘2’]
List<String> list = jpc.fromTerm(listTerm);
assertEquals("1", list.get(0));
assertEquals("2", list.get(1));
24
Java list of
Strings
Tuesday 9 July 13

38. A typed conversion example
Term listTerm = listTerm(new Atom("1"), new Atom("2"));
Type type = new TypeToken<ArrayList<Integer>>(){}.getType();
List<Integer> list = jpc.fromTerm(listTerm, type);
assertEquals(1, list.get(0));
assertEquals(2, list.get(1));
25
Tuesday 9 July 13

39. A typed conversion example
Term listTerm = listTerm(new Atom("1"), new Atom("2"));
Type type = new TypeToken<ArrayList<Integer>>(){}.getType();
List<Integer> list = jpc.fromTerm(listTerm, type);
assertEquals(1, list.get(0));
assertEquals(2, list.get(1));
25
type guiding conversion
Tuesday 9 July 13

40. A custom converter
public class StationConverter extends JpcConverter<Station, Compound> {
public static final String STATION_FUNCTOR = "station";
@Override public Compound toTerm(Station station, Jpc context) {
return new Compound(STATION_FUNCTOR, asList(new Atom(station.getName())));
}
@Override public Station fromTerm(Compound term, Jpc context) {
String stationName = ((Atom)term.arg(1)).getName();
return new StationJpc(stationName);
}
}
26
Tuesday 9 July 13

41. The type solver
• Attempts to infer the best Java type of a Prolog term if no
hint is available.
• Question:What does this term look like ?
[A-x,B-y,C-z]
• Answer: It may be a map.
27
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42. The instantiation manager
• A customizable mechanism for instantiating abstract classes/
interfaces if required.
• E.g. a Prolog list term may be mapped to a Java List or a Map.
• This manager knows which instance of List and Map to use (if
the given hint does not contain such information).
28
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43. LogicObjects
• A portable Java-Prolog linguistic symbiosis framework.
• Currently being migrated to JPC.
• Based on annotations for specifying mappings between Java-
Prolog artefacts.
• Support for context dependent mappings.
29
Tuesday 9 July 13

44. Symbiosis
30
“The intimate living together of two dissimilar organisms in a
mutually beneficial relationship.” (Merriam-Webster dictionary)
Tuesday 9 July 13

45. Linguistic symbiosis
• Objects from different worlds must understand each other.
• Invoking routines from another language as if they were defined
in their own language.
31
• Easier to achieve if the
languages belong to the
same paradigm.
Tuesday 9 July 13

46. A paradigm leak
“The event of concepts leaking from one programming paradigm
to another”
32
* Gybels, K.
SOUL and Smalltalk - Just Married: Evolution of the Interaction Between
a Logic and an Object-Oriented Language Towards Symbiosis.
In Proceedings of the Workshop on Declarative Programming in the Context
of Object-Oriented Languages. (2003)
*
Tuesday 9 July 13

47. The inhabitants of our two
worlds
33
The OO
world
The logic
world
Tuesday 9 July 13

48. The inhabitants of our two
worlds
33
Packages
Classes
Objects
Methods
Method invocations
Return values
The OO
world
The logic
world
Libraries
Modules
Terms
Clauses
Queries
Query solutions
Tuesday 9 July 13

49. Reducing the gap with Logtalk
34
The OO
world
The logic
world
Tuesday 9 July 13

50. Reducing the gap with Logtalk
34
The OO
world
The logic
world
Logtalk
An object-oriented layer
Tuesday 9 July 13

51. Case Study
35
The London underground
from:
Tuesday 9 July 13

52. Relevant concepts
36
The London underground
Tuesday 9 July 13

53. Relevant concepts
36
The London underground
stations
Tuesday 9 July 13

54. Relevant concepts
36
The London underground
stations
lines
Tuesday 9 July 13

55. Relevant concepts
36
The London underground
stations
linesmetro
Tuesday 9 July 13

56. Interesting relations
37
line1A C
line2
D
F
B
Tuesday 9 July 13

57. Interesting relations
37
line1A C
line2
D
F
B
Connected: Directly connected
(e.g., A with B).
connected
Tuesday 9 July 13

58. Interesting relations
37
line1A C
line2
D
F
B
Connected: Directly connected
(e.g., A with B).
Nearby: At most one intermediate
station, in the same line (e.g., A with C).
nearby
Tuesday 9 July 13

59. Interesting relations
37
line1A C
line2
D
F
B
Connected: Directly connected
(e.g., A with B).
Nearby: At most one intermediate
station, in the same line (e.g., A with C).
Reachable: Transitively connected
(e.g., A with F).
reachable
Tuesday 9 July 13

60. Interesting relations
38
Connected: Directly connected
(e.g., A with B).
Nearby: At most one intermediate
station, in the same line (e.g., A with C).
Reachable: Transitively connected
(e.g., A with F).
Easily expressed with
logic facts and rules
Tuesday 9 July 13

61. Which is the best language for
this problem?
• A logic language would let us express our problem using facts
and rules.
• But we sill want access to a modern OO language to develop
a user friendly interface.
• Then let’s do it with both through linguistic symbiosis.
39
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62. Implementation Strategy
• Develop the program in Prolog.
• Wrap it with an OO layer (Logtalk).
• Program the Java side using LogicObjects.
40
Tuesday 9 July 13

63. A rule based system using Prolog
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
41
Tuesday 9 July 13

64. A rule based system using Prolog
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
41
FACTS
Tuesday 9 July 13

65. A rule based system using Prolog
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
41
RULES
Tuesday 9 July 13

66. Adding an object-oriented layer
with Logtalk
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
42
:- object(metro).
:- end_object.
Tuesday 9 July 13

67. Adding an object-oriented layer
with Logtalk
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
42
:- object(metro).
:- end_object.
Tuesday 9 July 13

68. Adding an object-oriented layer
with Logtalk
connected(station(bond_street), station(oxford_circus), line(central)).
connected(station(oxford_circus), station(tottenham_court_road), line(central)).
...
nearby(S1,S2) :- connected(S1,S2,_).
nearby(S1,S2) :- connected(S1,S3,L), connected(S3,S2,L).
reachable(S1,S2,[]) :- connected(S1,S2,_).
reachable(S1,S2,[S3|Ss]) :- connected(S1,S3,_), reachable(S3,S2,Ss).
line(Name) :- setof(L, S1^S2^connected(S1,S2,L), Ls), list::member(line(Name), Ls).
42
:- object(metro).
:- end_object.
:- public([connected/3, nearby/2, reachable/3, line/1]). ACCESS MODIFIERS
Tuesday 9 July 13

69. Logtalk parametric objects
43
:- object(line(_Name)).
:- public([name/1, connects/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
:- object(station(_Name)).
:- public([name/1, connected/2, nearby/1, reachable/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
Tuesday 9 July 13

70. Logtalk parametric objects
43
:- object(line(_Name)).
:- public([name/1, connects/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
:- object(station(_Name)).
:- public([name/1, connected/2, nearby/1, reachable/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
PARAMETRIC OBJECT
Tuesday 9 July 13

71. Logtalk parametric objects
43
:- object(line(_Name)).
:- public([name/1, connects/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
:- object(station(_Name)).
:- public([name/1, connected/2, nearby/1, reachable/2]).
name(Name) :- parameter(1, Name).
...
:- end_object.
PARAMETRIC OBJECT
PARAMETRIC OBJECT
Tuesday 9 July 13

72. Invoking a Logtak method
Messages in Logtalk are expressed with the :: operator.
For example:
line(central)::connects(Station1, Station2)
Answers all the stations connected by the line ‘central’
44
Tuesday 9 July 13

73. Invoking a Logtak method
Messages in Logtalk are expressed with the :: operator.
For example:
line(central)::connects(Station1, Station2)
Answers all the stations connected by the line ‘central’
44
Tuesday 9 July 13

74. The Java world
45
public abstract class Line {
String name;
public Line(String name) {this.name = name;}
public abstract boolean connects(Station s1, Station s2);
public abstract int segments();
}
public abstract class Station {
...
}
public abstract class Metro {
...
}
Tuesday 9 July 13

75. The Java world
45
public abstract class Line {
String name;
public Line(String name) {this.name = name;}
public abstract boolean connects(Station s1, Station s2);
public abstract int segments();
}
public abstract class Station {
...
}
public abstract class Metro {
...
}
@LObject(args={“name”})
@LMethod(name={“connects”}, args={“_”, “_”})
@LObject(args={“name”})
Tuesday 9 July 13

76. Mapping objects from the two
worlds
46
Tuesday 9 July 13

77. Linguistic symbiosis challenges
• Translating objects to logic terms (and back).
• Mapping OO methods to logic queries.
• Dealing with unbound variables.
• Returning values from queries.
• Managing multiplicity.
47
* Some of them presented a bit differently in:
D'Hondt, Maja and Gybels, Kris and Jonckers, Viviane.
Seamless integration of rule-based knowledge and object-
oriented functionality with linguistic symbiosis.
In Proceedings of the 2004 ACM symposium on Applied computing,
SAC '04, pages 1328{1335, New York, NY, USA, 2004. ACM.
*
Tuesday 9 July 13

78. 48
Translating objects to logic terms
Tuesday 9 July 13

79. 48
Translating objects to logic terms
Tuesday 9 July 13

80. 48
Translating objects to logic terms
Tuesday 9 July 13

81. public abstract class Metro {...}
@LObject(name = "my_metro")
public abstract class Metro {...}
@LObject(args = {"name"})
public abstract class Line {
private String name;
...
}
metro
my_metro
line(l_name)
Translating objects to logic terms
49
Java Logtalk
Tuesday 9 July 13

82. public abstract class Metro {...}
@LObject(name = "my_metro")
public abstract class Metro {...}
@LObject(args = {"name"})
public abstract class Line {
private String name;
...
}
metro
my_metro
line(l_name)
Translating objects to logic terms
49
Java Logtalk
Tuesday 9 July 13

83. public abstract class Metro {...}
@LObject(name = "my_metro")
public abstract class Metro {...}
@LObject(args = {"name"})
public abstract class Line {
private String name;
...
}
metro
my_metro
line(l_name)
Translating objects to logic terms
49
Java Logtalk
Tuesday 9 July 13

84. public abstract class Metro {...}
@LObject(name = "my_metro")
public abstract class Metro {...}
@LObject(args = {"name"})
public abstract class Line {
private String name;
...
}
metro
my_metro
line(l_name)
Translating objects to logic terms
49
Java Logtalk
Tuesday 9 July 13

85. Mapping Java methods to Logtalk
methods
50
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
line(l_name)::connects(
station(s1_name), station(s2_name)).
line(l_name)::connects(_, _).
Java Logtalk
Tuesday 9 July 13

86. Mapping Java methods to Logtalk
methods
50
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
line(l_name)::connects(
station(s1_name), station(s2_name)).
line(l_name)::connects(_, _).
Java Logtalk
Tuesday 9 July 13

87. Mapping Java methods to Logtalk
methods
50
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
line(l_name)::connects(
station(s1_name), station(s2_name)).
line(l_name)::connects(_, _).
Java Logtalk
Tuesday 9 July 13

88. Mapping Java methods to Logtalk
methods
50
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
line(l_name)::connects(
station(s1_name), station(s2_name)).
line(l_name)::connects(_, _).
Java Logtalk
Tuesday 9 July 13

89. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
51
Dealing with unbound variables in
method calls
Tuesday 9 July 13

90. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
51
first Java method parameter
(as term)
Dealing with unbound variables in
method calls
Tuesday 9 July 13

91. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
51
first Java method parameter
(as term)
unbound
logic variable
Dealing with unbound variables in
method calls
Tuesday 9 July 13

92. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
51
station(s1_name)::reachable(station(s2_name), IntermediateStations)
Dealing with unbound variables in
method calls
Tuesday 9 July 13

93. 52
Interpreting a query result as a
Java object
The logic solutions
Varx1 x1, Vary1 y1
Varx2 x2, Vary2 y2
Varxn xn, Varyn yn
Tuesday 9 July 13

94. 52
Interpreting a query result as a
Java object
The logic solutions
Varx1 x1, Vary1 y1
Varx2 x2, Vary2 y2
Varxn xn, Varyn yn
(set of frames binding logic
variables to terms)
frame 1
frame 2
frame n
Tuesday 9 July 13

95. 53
Interpreting a query result as a
Java object
The logic solutions
Varx1 x1, Vary1 y1
Varx2 x2, Vary2 y2
Varxn xn, Varyn yn
(set of frames binding logic
variables to terms)
Tuesday 9 July 13

96. 53
Interpreting a query result as a
Java object
The logic solutions The method return value
Varx1 x1, Vary1 y1
Varx2 x2, Vary2 y2
aJavaObject
Varxn xn, Varyn yn
(set of frames binding logic
variables to terms)
Tuesday 9 July 13

97. 54
Returning values from one
solution
The logic solutions The method return value
term(Varx1, Vary1)
Varx1 x1, Vary1 y1 term(x1, y1)
Varx2 x2, Vary2 y2 term(x2, y2)
Varxn xn, Varyn yn term(xn, yn)
(set of frames binding logic
variables to terms)
Tuesday 9 July 13

98. 54
Returning values from one
solution
The logic solutions The method return value
term(Varx1, Vary1)
Varx1 x1, Vary1 y1 term(x1, y1)
Varx2 x2, Vary2 y2 term(x2, y2)
Varxn xn, Varyn yn term(xn, yn)
(set of frames binding logic
variables to terms)
(specified in a method
with @LSolution)
Tuesday 9 July 13

99. 54
Returning values from one
solution
The logic solutions The method return value
term(Varx1, Vary1)
Varx1 x1, Vary1 y1 term(x1, y1)
Varx2 x2, Vary2 y2 term(x2, y2)
Varxn xn, Varyn yn term(xn, yn)
(set of frames binding logic
variables to terms)
(specified in a method
with @LSolution)
(default solution)
Tuesday 9 July 13

100. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
55
Explicitly specification of return
values
Tuesday 9 July 13

101. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
55
Explicitly specification of return
values
Tuesday 9 July 13

102. @LObject(args = {"name"})
public abstract class Station {
@LSolution("IntermediateStations")
@LMethod(name = "reachable", args = {"$1", "IntermediateStations"})
public abstract List<Station> intermediateStations(Station station);
...
}
55
Explicitly specification of return
values
Tuesday 9 July 13

103. @LObject(args = {"name"})
public abstract class Station {
@LMethod(name = "reachable", args = {"$1", "LSolution"})
public abstract List<Station> intermediateStations(Station station);
...
}
56
Implicit specification of return
values
Tuesday 9 July 13

104. @LObject(args = {"name"})
public abstract class Station {
@LMethod(name = "reachable", args = {"$1", "LSolution"})
public abstract List<Station> intermediateStations(Station station);
...
}
56
Implicit specification of return
values
Tuesday 9 July 13

105. Managing multiplicity
57
• A logic routine can have many solutions, in Java only one.
• Multiple values can be grouped with @LComposition.
• The kind of container to return depends on the method
signature.
• The kind of object in the container is also extracted from the
method signature.
Tuesday 9 July 13

106. 58
Returning multiple values from
queries
The logic solutions The method return value
term(Varx1, Vary1)
Varx1 x1, Vary1 y1 term(x1, y1)
Varx2 x2, Vary2 y2 term(x2, y2)
Varxn xn, Varyn yn term(xn, yn)
Tuesday 9 July 13

107. 58
Returning multiple values from
queries
The logic solutions The method return value
term(Varx1, Vary1)
Varx1 x1, Vary1 y1 term(x1, y1)
Varx2 x2, Vary2 y2 term(x2, y2)
Varxn xn, Varyn yn term(xn, yn)
(a composed solution)
Tuesday 9 July 13

108. @LObject(args = {"name"})
public abstract class Station {
...
@LComposition @LSolution("S")
@LMethod(args = {"S"})
public abstract List<Station> nearby();
}
59
station(aName)::nearby(S).
LogtalkJava
Returning multiple values from
queries
Tuesday 9 July 13

109. @LObject(args = {"name"})
public abstract class Station {
...
@LComposition @LSolution("S")
@LMethod(args = {"S"})
public abstract List<Station> nearby();
}
59
station(aName)::nearby(S).
LogtalkJava
Returning multiple values from
queries
Tuesday 9 July 13

110. @LObject(args = {"name"})
public abstract class Station {
...
@LComposition @LSolution("S")
@LMethod(args = {"S"})
public abstract List<Station> nearby();
}
59
station(aName)::nearby(S).
LogtalkJava
Returning multiple values from
queries
Tuesday 9 July 13

111. @LObject(args = {"name"})
public abstract class Station {
...
@LComposition @LSolution("S")
@LMethod(args = {"S"})
public abstract List<Station> nearby();
}
59
container type
station(aName)::nearby(S).
LogtalkJava
Returning multiple values from
queries
Tuesday 9 July 13

112. @LObject(args = {"name"})
public abstract class Station {
...
@LComposition @LSolution("S")
@LMethod(args = {"S"})
public abstract List<Station> nearby();
}
59
each solution type
container type
station(aName)::nearby(S).
LogtalkJava
Returning multiple values from
queries
Tuesday 9 July 13

113. Returning a property of the result
set
60
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
Tuesday 9 July 13

114. Returning a property of the result
set
60
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
should return if logic method succeeds or not
Tuesday 9 July 13

115. Returning a property of the result
set
60
@LObject(args = {"name"})
public abstract class Line {
private String name;
public abstract
boolean connects(Station s1, Station s2);
@LMethod(name = "connects", args = {"_", "_"})
public abstract
int segments();
}
should return if logic method succeeds or not
should return the number of solutions
Tuesday 9 July 13

116. Instantiating a symbiotic object in
Java
Line line = newLogicObject(Line.class, “central”);
System.out.println("Number of segments of line " + line + ": " + line.segments());
61
Tuesday 9 July 13

117. Instantiating a symbiotic object in
Java
Line line = newLogicObject(Line.class, “central”);
System.out.println("Number of segments of line " + line + ": " + line.segments());
61
Tuesday 9 July 13

118. Instantiating a symbiotic object in
Java
Line line = newLogicObject(Line.class, “central”);
System.out.println("Number of segments of line " + line + ": " + line.segments());
61
Tuesday 9 July 13

119. Other features
• Java expressions embedded in logic terms (symbiosis terms).
• Dependency management.
• Integration with plain Prolog (without Logtalk).
62
Tuesday 9 July 13

120. Future work
• Finishing a full two-ways linguistic symbiosis framework.
• Supporting more Prolog engines.
• Adding support to other kinds of integration techniques (e.g.
serialization and objects references).
• Continue the development of reusable hybrid components.
63
Tuesday 9 July 13

121. Inspiration from other domains
• Interoperability layer: JDBC.
• Mapping of artefacts using annotations: JAXB.
• Context dependent conversions: GSON.
• Linguistic symbiosis concepts: SOUL.
64
Tuesday 9 July 13

122. Conclusions
• We have provided portable and simple solutions for many
issues concerning Java-Prolog interoperability.
• We are actively exploring how far we can get in automation/
transparency regarding Java-Prolog linguistic symbiosis.
• We are targeting complex heterogeneous realistic scenarios.
• We are attempting to provide reusable hybrid components
and frameworks that may be helpful to the community.
65
Tuesday 9 July 13

123. Thanks
66
Tuesday 9 July 13