The core of the second generation Topic Maps standards (TMDM, XTM2.0) has been finalized, yet the uptake is still slow. In this paper, we highlight engineering considerations for a novel backend for the TM4J open source topic maps engine, which is currently in development, but already usable for some purposes. As the name suggests, the “TMDM” backend is designed to reflect the TMDM specification closely. In fact, it is much closer to the TMDM than to the internal legacy TM4J data model (which is based on the XTM 1.0 data model). This motivates a bridging layer between the TMDM and the XTM 1.0 data model. We emphasize how merging is implemented in the “TMDM” backend and conclude with some synthetic merging benchmarks of the current “TMDM” backend prototype.

1. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Towards a second generation
Topic Maps Engine
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 1 of 27

2. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Overview
technical talk
API design
multiple layers
event handling
merging done slowly or fastly
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 2 of 27

3. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Objectives
need a Java TM engine
with TMDM support
semantically
syntactically (names of methods match TMDM)
with instant merging
with dynamic (reversable) merging
with support for modern Java 1.5 features (generics, etc.)
which can act as backend for TM4J1 applications
with persistence support
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 3 of 27

4. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Idea
develop a new backend for TM4J
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 4 of 27

5. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
„TMDM“ backend
is layered
is (currently) RAM-only
can do topic merging fast
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 5 of 27

6. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Layers
what?
layer ≈ coverage of all TMDM item types under a
particular concern
why?
separation of concerns: do one thing, and do it well
modularity of architecture:
replace a layer implementation
by another layer implementation
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 6 of 27

7. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Layers
how?
layer ≈ set of classes and interfaces in one Java package
communication between layers by
method calls
event listeners (later)
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 7 of 27

8. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Layers
which?
one layer for accessing a topic map
one layer for just reading a topic map
one layer for storing a topic map
one layer for merging a topic map
one layer for compatibility with TM4J1
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 8 of 27

9. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TMDM read-write interfaces layer
Concern: accessing a topic map
set of interfaces in package org.tm4j.topicmap.tmdm:
TopicMap extends Reifiable
Topic extends TopicMapConstruct
TopicName extends Scopeable
Variant extends Scopeable
Occurrence extends Scopeable
Association extends Scopeable
AssociationRole extends Reifiable
Scopeable extends Reifiable
Scope
Reifiable extends TopicMapConstruct
TopicMapConstruct
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 9 of 27

10. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Example: AssociationRole
public interface AssociationRole extends Reifiable,
ReadableAssociationRole {
public ReadableTopic getType();
public ReadableTopic getPlayer();
public Association getParent();
public void setType(Topic type);
public void setPlayer(Topic player);
}
note: no setter for parent.
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 10 of 27

11. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TMDM read-only interfaces layer
Concern: just reading a topic map
set of interfaces in package org.tm4j.topicmap.tmdm:
ReadableTopicMap
ReadableTopic
ReadableTopicName
ReadableVariant
ReadableOccurrence
ReadableAssociation
ReadableAssociationRole
ReadableScopeable
ReadableScope
ReadableReifiable
ReadableTopicMapConstruct
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 11 of 27

12. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Example: ReadableOccurence
public interface ReadableOccurrence extends ReadableScopeable {
public ReadableTopic getType();
public Locator getDatatype();
public String getValue();
public ReadableTopic getParent();
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 12 of 27

13. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TMDM Basic implementation layer
Concern: storing a topic map
set of classes in package org.tm4j.topicmap.tmdm.basic:
BasicTopicMap
BasicTopic
BasicTopicName
BasicVariant
BasicOccurrence
BasicAssociation
BasicAssociationRole
BasicScopeable
BasicScope
BasicReifiable
BasicTopicMapConstruct
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 13 of 27

14. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Example: BasicAssociation
public class BasicAssociation extends BasicScopeable
implements Association {
BasicTopicMap parent;
BasicTopic type;
Set<BasicAssociationRole> toles;
protected BasicAssociation(BasicTopicMap parent,
BasicTopic type,BasicScope scope)
public BasicTopicMap getParent()
public void setType(Topic type)
public void setType(BasicTopic type)
public BasicTopic getType()
public BasicAssociationRole createRole(Topic type,Topic player)
public BasicAssociationRole createRole(BasicTopic type,
BasicTopic player)
public Set<BasicAssociationRole> getRoles()
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 14 of 27

15. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TMDM Merged implementation layer
Concern: merging a topic map
set of classes in package org.tm4j.topicmap.tmdm.merged:
MergedTopicMap
MergedTopic
MergedTopicName
MergedVariant
MergedOccurrence
MergedAssociation
MergedAssociationRole
MergedScopeable
MergedScope
MergedReifiable
MergedTopicMapConstruct
MergedTopicMapView
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16. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
MergedTopicMapConstruct
public abstract class MergedTopicMapConstruct<I extends ReadableTopicMapConstruct>
extends TMDMObject
implements ReadableTopicMapConstruct {
protected List<I> components;
protected MergedTopicMapView container;
protected MergedTopicMapConstruct(MergedTopicMapView container)
protected MergedTopicMapConstruct(MergedTopicMapView container,I firstComponent)
protected MergedTopicMapView getContainer()
public boolean containsComponent(I component)
protected void addComponent(I component)
protected void removeComponent(I component)
public Collection<I> getComponents()
public I getRandomComponent()
public Set<Locator> getItemIdentifiers()
protected Collection<Set<Locator>> getItemIdentifiersSetCollection()
public Set<Locator> getItemIdentifiersSet()
public Collection<Locator> getItemIdentifiersCollection()
protected boolean containsItemIdentifier(Locator itemIdentifier)
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 16 of 27

17. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Example: MergedAssociationRole
public class MergedAssociationRole
extends MergedReifiable<ReadableAssociationRole,MergedAssociationRoleKey>
implements ReadableAssociationRole {
protected MergedAssociationRole(MergedTopicMapView container,
MergedAssociationRoleKey key,
ReadableAssociationRole firstComponent) {
super(container,key,firstComponent);
}
public MergedTopic getType() {
return getContainer().getMergedTopic(getRandomComponent().getType());
}
public MergedTopic getPlayer() {
return getContainer().getMergedTopic(getRandomComponent().getPlayer());
}
public MergedAssociation getParent() {
return getContainer().getMergedAssociation(getRandomComponent().getParent());
}
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 17 of 27

18. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TM4J1 compatibility layer
Concern: exposing a TMDM layer topic map using the TM4J1 API
set of classes in package org.tm4j.topicmap.tmdm.tm4j1:
TopicMapImpl
TopicImpl
BaseNameImpl
VariantImpl
OccurrenceImpl
AssociationImpl
MemberImpl
ScopedObjectImpl
TopicMapObjectImpl
Wrap around TMDM to provide TM4J1 (=XTM1) semantics
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 18 of 27

19. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TopicMapObjectImpl
public abstract class TopicMapObjectImpl<
I extends org.tm4j.topicmap.tmdm.TopicMapConstruct,
V extends org.tm4j.topicmap.tmdm.ReadableTopicMapConstruct>
implements org.tm4j.topicmap.TopicMapObject {
protected I representedObject;
protected TopicMapImpl container;
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 19 of 27

20. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Event Handling
Basic idea: make event firing just a method call
Thus:
all event parameters are method call parameters
default implementation: empty method
Rationale
keep it small and simple
(let the JVM) optimize away unnecessary method calls
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 20 of 27

21. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
TopicMapEventListener
public interface TopicMapEventListener<TM extends ReadableTopicMap,
T extends ReadableTopic,
A extends ReadableAssociation,
O extends ReadableOccurrence,
TMC extends ReadableTopicMapConstruct,
TN extends ReadableTopicName,
V extends ReadableVariant,
AR extends ReadableAssociationRole> {
public void notifyTopicCreated(TM topicMap,T topic);
public void notifyTopicRemoved(TM topicMap,T topic);
public void notifySubjectIdentifierAdded (TM topicMap,T topic,Locator sid);
public void notifySubjectIdentifierRemoved(TM topicMap,T topic,Locator sid);
public void notifySubjectLocatorAdded (TM topicMap,T topic,Locator sid);
public void notifySubjectLocatorRemoved (TM topicMap,T topic,Locator sid);
public void notifyItemIdentifierAdded (TM topicMap,TMC topicMapConstruct,
Locator itemIdentifier) throws
DuplicateItemIdentifierException;
public void notifyItemIdentifierRemoved (TM topicMap,TMC topicMapConstruct,
Locator itemIdentifier);
}
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 21 of 27

22. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Peculiarities
Scope is a first-class class
replace the set of all themes by a pointer
# of distinct scopes is small, thus
# of distinct Scope objects is small
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 22 of 27

23. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Bigger picture
TM4J1 compatibility layer
container container
TopicImpl TopicImpl TopicMapImpl
representedObject representedObject
parent parent
BasicTopic BasicTopic BasicTopicMap
Basic layer
components components
Merged layer
MergedTopic MergedTopicMap
container container
topicToMergedTopic
mergedTopicMap
MergedTopicMapView eventListener
TopicMapEventListener
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 23 of 27

24. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Merging
„A merge B = C“ is slow O(n²)
„A merge B = B“ is fast O(n·log(n))
if A is smaller than B
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 24 of 27

25. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Merging Benchmark
processing time
900
825,49
800
processing time in seconds
700
“memory” backend
600 “TMDM” backend (no merging optimization)
“TMDM” backend (with merging optimization)
500
458,97
400
300
200
100
21,51
0
0 40000 80000 120000
# TopicMapConstructs
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 25 of 27

26. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
What to do?
instantaneous unmerging
computationally expensive
Should we support it? What to do if not?
implement some methods
autogenerate engine (Domain Specific Languages)
late merging vs. early merging
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 26 of 27

27. TMRA 2008: Towards a second generation Topic Maps engine
2008-10-17
Thank you
Questions?
Xuân Baldauf <xuan--tm4j2--2008--tmra.de@baldauf.org>, Robert Amor <trebor@cs.auckland.ac.nz> 27 of 27