PURPOSE

A NetLogo case based reasoning toolkit, cbr as a NetLogo plugin.

INSTALLATION

See the install document

BUILD

See the build document

MANIFEST

• BUILD.md - the build instructions
• INSTALL.md - how to install the plug-in in NetLogo
• bin - directory where all the scripts and compiled classes are stored. Be careful some IDEs automatically clear this directory on a clean - there are useful scripts that are not automatically generated present in this directory.
• doc - documentation directory. Contains documentation. Be careful some IDEs automatically clear this directory on a clean - there are useful files that are not automatically generated present in this directory.
• INSTALL.md - instructions on how to install the plug-in.
• jar-manifest.txt - manifest used to create the cbr.jar - the plugin.
• lib - required libraries - these are already present in NetLogo.
• LICENSE.txt - How you may use this plugin.
• MANUAL.md
• paper - A paper describing the plugin.
• PUBLISHING.md - the instructions on how to release for use as a published NetLogo extension.
• README.md - this file.
• src - The source code for the plugin. Normally this would be something like src\uk\ac\hutton\cbr or whatever. The problem with this is that the plugin extension for NetLogo makes it difficult to adopt this structure, therefore is just bunged in src where all classes share the default package space.
• test - A test NetLogo model. Normally we would used automated testing. The problem with this is setting up things like the Context is rather involved in NetLogo, so we use a NetLogo model to test the plug-in. There is a README.md in this directory with instructions on how to do this. Also the actual plugin jar cbr.jar is in a subdirectory cbr, which is the jar you need to install the plugin.
• TODO - list of outstanding tasks to complete on the plugin.
• tutorial - a presentation giving a brief explanation of how to use the NetLogo extension
• UPGRADING.md - instructions on what to change if you should have to upgrade the version of NetLogo.
• CITATION.cff - used by Zenodo to generate the citation required for this software.

INSTRUCTIONS

See also the manual

WHAT IS IT?

This is an example of how to use the case based reasoning plugin.

HOW IT WORKS

The code implements a reference version of code using the extension that is described here.

Select the run-testing button to make sure that the code is behaving as it should. If there is no error dialogue then the code is working as expected. The code also shows how to the use the extension.

Normally a case base consists of a series of cases, each of these cases consist of

• state
• decision/activity
• outcome

The state can be anything such as the bank balance of the agent. The decision/activity might be to install central heating. The outcome might be straight forwardly yes or no. It might be probability, or it might some arbitrary decision/activity metric for use elsewhere.

A state and decision/activity are presented to the case base. The case base is searched for the closest match (if there is one) and the outcome of that match is given.

A NetLogo case consists of a state in any of the standard Netlogo variables, such as list, number, string, etc. This is strictly defined by the cbr:lambda which is the comparator program used to determine the "distance" the three cases:

• case A
• case B
• referent case R

are relative to ecah other. That is, if:

• the case A is 'closer' to the referent case R than the case B using cbr:lamda to the referent case R then cbr:lt is returned
• the case B is 'closer' to the referent case R than the case A using cbr:lamda to the referent case R then cbr:gt is returned
• the case B is 'same distance' to the referent case R than the case A using cbr:lamda to the referent case R then cbr:eq is returned
• the case B is 'closer' using cbr:lamda to the referent case R then cbr:lt is returned

The cbr:lamda is then used by cbr:match or cbr:matches to determine a single closest match of a "hypothetical" case that is presented to cbr:match or more or one equally close matches if cbr:matches is used. The case will consists of a state and decison and returning the 'best match' base on the repeated use of cbr:lamda to determine which is the closest match. If the match does not meet a suitable criterion then cbr:incmp is returned.

When using cbr:match, then if there are more than one match then the case with the highest rank is returned, or failing that the oldest. If both these conditions are equal then the result is a random selection from among those cases. More than one case may be returned if cbr:matches is used.

If no cbr:lamba is provided then a default lambda is used. The specification for this is as follows.

The comparison algorithm always has three arguments:

• Case A
• Case B
• Referent case R

Cases A and B need not be in a case base; they may also have empty Decision and Outcome parts, or simply be a State. Case R may have empty Decision and Outcome parts, or simply be a State. (In a typical use-case, R is an ‘expected state of the world’ for which the deciding agent is trying to find a range of cases.)

The algorithm returns one of four responses:

• cbr:gt – iff A more similar to R than B
• cbr:lt – iff B more similar to R than B
• cbr:eq – iff A and B are equally similar to R
• cbr:incmp – iff A and B are not comparably similar to R

HOW TO USE IT

The primitives available are:

cbr:new

Instantiates a case base object.

Parameters

None

Returns

• case base object

cbr:add

Parameters

Adds a case the the NetLogo case base object. The tick at which this takes place is also recorded and can be accessed using cbr:get-time. This property can be manipulated by usingcbr:set-time

Note the case object cannot exist independently of the case base object. If the latter is destroyed or removed, then so to is the former.

• case base object

• state (in a form that cbr:lamda requires for doing the "distance" function.

• decision/activity (in a form that cbr:lamda requires for doing the "distance" function.

• outcome (in any form that you require, providing this is not used as part of the decison making in cbr:lamda).

Returns

Returns a case object. This is not really useful, but can be used for display and debugging uses if needs be.

cbr:combine

All the cases from the second case base are appended to the case base in the first argument

Parameters

• a to case base object
• a from case base oject

Returns

Nothing.

cbr:all

Used to return all the cases in a specific case base.

Parameters

• case base object

Returns

A NetLogo list of all the cases in the case base object.

cbr:remove

Removes a particular case from a case base.

Parameters

• case base object

• case object (returned when the case is created)

Returns

Nothing.

cbr:state

This is a reporter on the state contained within a case object.

Parameters

• case base object

• case object

Returns

A state in the form the cbr:lamda uses. In the example code showed above this takes the form of a list of strings.

cbr:decision

This is a reporter on the decision/activity contained within a case object.

Parameters

• case base object

• case object

Returns

A decision in the form the cbr:lamda uses. In the example code showed above this takes the form of a string.

cbr:outcome

This is a reporter on the outcome of a case.

Parameters

• case base object

• case object

Returns

In the example code showed above this takes the form of a list of booleans.

cbr:set-time

Time is used in conjunction cbr:forget to remove aged cases from the case base. The time is 0 or a postive number and corresponds to the number of ticks.

Parameters

• case base object

• case object (returned when the case is created)

• number of ticks representing when the case was entered into the case base table.

Returns

Nothing.

cbr:get-time

Obtains/gets the time of origin on a particular case within a case base object. This is measured in number of ticks, is 0 or positive. Time is used in conjunction cbr:forget to remove aged cases from the case base.

Parameters

• case base object

• case object within the above case base

Returns

A number of ticks, representing when the case was added to the case base. This is generally the current cclick but may be manipulated using cbr:set-time.

cbr:set-earliest

This sets the earliest tick. If a case base has a creation time (as a tick) older than this, then upon the evocaction of the next cbr:forget then this case will be deleted, i.e. forgotten.

Parameters

• case base object

• number representing the oldest tick, before which if any case is stamped with an earlier time then these cases will be removed upon invocation of cbr:forget. The number in this case corresponds to the number of ticks.

Returns

Nothing.

cbr:forget

If the cbr:set-earliest has been used, then cbr:forget will enforce this limit. We have done it this way to prevent exceptions being thrown if the this limit is exceeded, thus it requires explicit invocation via the user to make the case base forget.

A tick is used to denote time. A NetLogo case base will have as part of its metadata the time before which all cases acquired at that time will be forgotten. This property may be obtained using the cbr:get-earliest and by default is set to 0.

The actual age of a case within a casebase can be manipulated with the use of cbr:set-time and cbr:get-time.

cbr:lambda

This may the reporter that does distance comparison. This is never called directly If a cbr:lambda is not provided, then the default comparator is called. The default comparator has the following specification.

The algorithm should do the following:

1. If R is a case, then set R to the State part of the case

2. If A is a case, then set A to the State part of the case

3. If B is a case, then set B to the State part of the case

4. We now consider different datatypes for R, A and B in S = { number } and M = { string, patch, turtle, link, list, agent set } a N. B. S is a set of scalar datatypes; M is a set of multidimensional datatypes

5. If R, A and B are not the same datatype, return cbr:incmp

6. If R, A and B are all numbers, then if abs (R – A) < abs(R – B) return cbr:gt; else if abs (R – A) > abs(R – B) return cbr:lt; else return cbr:eq

7. If R, A and B are all agent sets, then let Am = A – (A intersect B) and let Bm = B – (A intersect B). If Am and Bm are both empty, return cbr:eq. Let AmR = Am – (Am intersect R); Let BmR = Bm – (Bm intersect R); Let AR = A intersect R; Let BR = B intersect R. If AR is a superset of BR and AmR is a subset of BmR, return cbr:gt; Else if BR is a superset of AR and BmR is a subset of AmR, return cbr:lt; Else return cbr:incmp Basic principle: A is more similar to R than B is if all agents that B has in common with R, A also has in common with R, and all agents that A does not have in common with R, B also does not have in common with R. If there are members of R that are members of A but not B, and there are also members of R that are members of B but not A, then A and B are incomparably similar to R; likewise, if we look at members of A and B that are not members of R, unless one is a subset-of-or-equal-to the other, A and B are incomparably similar. The diagram below shows the three conditions in which the agent set comparisons are not incomparable. Note that in the left one, if B – (A intersect B) is empty, A is still more similar than B to R; also, if A – (A intersect B) is empty, A is still more similar to R. If both those regions are empty, then A and B are equal. The corresponding points are true of the middle diagram (i.e. with A and B swapped).

8. If A, B and R are all lists, then let answer = cbr:eq. For i in 1:min(length of A, length of B, length of R): if A[i] == R[i] and B[i] != R[i], then if answer == cbr:lt, return cbr:incmp; else let answer = cbr:gt. Else if B[i] == R[i] and A[i] != R[i], then if answer == cbr:gt, return cbr:incmp; else let answer = cbr:lt. End For. If answer == cbr:gt and A has the shortest length and and For all j in (i + 1):min(length of B, length of R), B[j] != R[j], then return cbr:gt. If answer == cbr:lt and B has the shortest length and For all j in (i + 1):min(length of A, length of R), A[j] != R[j], then return cbr:lt. If A and B have different lengths, return cbr:incmp. If For all j in (i + 1):(length of A), A[j] == B[j], then return cbr:equal else return cbr:incmp Basic principle: A is more similar-to R than B if everywhere that B is equal to R, A is also equal to R

9. If A, B and R all being strings can work on the same basis as lists, with i and j indexing characters.

10. If A, B and R are all patches then they can also be handled similarly to lists – each of the default and declared patches-own variables would be put into the lists in the same order.

This is the comparator used in the test program to which this documentation is attached.

Parameters

• case base object

• An anonymous reporter or named reporter, which must take four parameters

  • case base object
  • case A
  • case B
  • referent case R

Returns

This must return one of the following

• cbr:lt
• cbr:gt
• cbr:incmp
• cbr:eq

The current represantion that cbr:lamda must return if of the three cases

• case A;
• case B, and
• referent case R,

when the case A and the case B "are an equal distance" from the referent case R.

cbr:eq

This is used to standardise response from cbr:lamda so cbr:match and cbr:matches will work correctly with it.

Parameters

The current represantion that cbr:lamda must return if of the three cases

• case A;
• case B, and
• referent case R,

when the case A is "equal" distance from the referent case R as the case B.

cbr:gt

This is used to standardise response from cbr:lamda so cbr:match and cbr:matches will work correctly with it.

Parameters

None

Returns

The current represantion that cbr:lamda must return if of the three cases

• case A;

• case B, and

• referent case R,

• case A;

• case B, and

• referent case R,

when the case A is "further" from the referent case R than the case B.

cbr:lt

This is used to standardise response from cbr:lamda so cbr:match will work correctly with it.

Parameters

None

Returns

The current represantion that cbr:lamda must return if of the three cases

• case A;
• case B, and
• referent case R,

when the case A is "closer" to the referent case R than the case B.

cbr:incmp

Parameters

• None

Returns

The current represantion that cbr:lamda must return if any of the three cases

• case A;
• case B, and
• referent case R,

cannot be used for comparison.

cbr:get-earliest

This gets the earliest time at which a case in a casebase will have been created at. Before this tick if cbr:forget is called then all cases with the casebase that have a time stamp (when they were notionally create) less than this value, then these cases will be deleted from the case base.

Parameters

• case base object

Returns

• A number which is the maxiumum number of cases the case base can contain.

cbr:set-earliest

This gets the earliest time at which a case in a casebase will have been created at. Before this tick if cbr:forget is called then all cases with the casebase that have a time stamp (when they were notionally create) less than this value, then these cases will be deleted from the case base.

Parameters

• case base object

• A number representing a tick.

Returns

Nothing.

cbr:set-max-size

This gets the maxium size for the case base. That is the maxiumum number of cases it may contain. The case base may actually contain more cases than this number and it requires the specific invocation of cbr:resize to enforce this size restriction. Upon the invocation of cbr:resize those case with the lowest rank will be deleted. If there are two cases with equal rank then the oldest will then be deleted.

Parameters

• case base object

• A number which is the maxiumum number of cases the case base can contain.

Returns

Nothing.

cbr:get-max-size

This sets the maxium size for the case base. That is the maxiumum number of cases it may contain. The case base may actually contain more cases than this number and it requires the specific invocation of cbr:resize to enforce this size restriction. Upon the invocation of cbr:resize those case with the lowest rank will be deleted. If there are two cases with equal rank then the oldest will then be deleted.

Parameters

• case base object

• A number which is the maxiumum number of cases the case base can contain.

Returns

Nothing.

cbr:set-rank

This sets the rank on a particular case in a case base. When choosing between two cases when decreasing the size of a case base to a specified maximum number of cases, then to determine which cases should be deleted to reduce the size of the case base, we use the concept of the rank. All cases start with 0 rank. However, this rank can be set using this primitive, and any case with a higher rank will be preferred when retaining cases.

Parameters

• case base object

• a number representing the rank of the case. The higher the rank, the more likely it is that the case will survive.

Returns

Nothing.

cbr:get-rank

This gets the rank on a particular case in a case base. When choosing between two cases when decreasing the size of a case base to a specified maximum number of cases, then to determine which cases should be deleted to reduce the size of the case base, we use the concept of the rank. All cases start with 0 rank. However, this rank can be set using this primitive, and any case with a higher rank will be preferred when retaining cases.

Parameters

• case base object

Returns

Nothing.

cbr:resize

This resizes the case base to the number of cases specified by cbr:set-max-size. When choosing between two cases when decreasing the size of a case base to a specified maximum number of cases, then to determine which cases should be deleted to reduce the size of the case base, we use the concept of the rank. All cases start with 0 rank. However, this rank can be set using this primitive, and any case with a higher rank will be preferred when retaining cases.

This command is explicit. It has been done this way for two reasons. Firstly this gives control to the user and secondly the only way to interrupt the work flow in NetLogo appears to be some kind of exception. This, of course means that the number of cases in a case base can exceed this number. Again this is intentional and the number can be checked using the code length cbr:all some-case-base.

Parameters

• case base object

Returns

Nothing.

cbr:match

This returns the closet matched case that matches the state in the state parameter and the decision/activity that has been selected.

Parameters

• case base object

• state in a format that can be use by cbr:lambda to do the distance assessment between cases, which describes the necessary state of the agent)

• decision/activity in a format that can be use by cbr:lambda to do the distance assessment between cases, which describes the decision or activity that is the agent is about to make or perform).

Returns

Nobody if there is no match otherwise returns a match case from the case base, which then may be interrogated using

• cbr:state
• cbr:decision
• cbr:outcome

The first two can be used to validate the case the last is usually what we are after in terms of makeing a decision.

This will return only one case based on the selection criteria mentioned in the "HOW IT WORKS" section above.

cbr:matches

This returns the set of closest matched cases that match the state in the state parameter and the decision/activity that has been selected.

Parameters

• case base object

• state in a format that can be use by cbr:lambda to do the distance assessment between cases, which describes the necessary state of the agent)

• decision/activity in a format that can be use by cbr:lambda to do the distance assessment between cases, which describes the decision or activity that is the agent is about to make or perform).

Returns

Nobody if there is no match otherwise returns a list of cases from the case base, which then may be interrogated using

• cbr:state
• cbr:decision
• cbr:outcome

The first two can be used to validate the case the last is usually what we are after in terms of makeing a decision.

THINGS TO NOTICE

(suggested things for the user to notice while running the model)

THINGS TO TRY

The typical workflow is

1. instantiate a case base using cbr:new
2. add some cases to it using cbr:add
3. query the case base using either cbr:match or cbr:matchess to return one or more cases
4. Interrogate the returned case outcome to see what the case base recommends.

In addition to this you might to add the resultant state, decision and outcome back into the case base in order to emulate memory.

EXTENDING THE MODEL

As mentioned above you can write your own default comparator. Here is an example of how to do this.

to-report new-comparator [some-case-base yes-case no-case reference-case]
  let yes-state cbr:state some-case-base yes-case
  let no-state cbr:state some-case-base no-case
  let reference-state cbr:state some-case-base reference-case

  if (cbr:decision some-case-base yes-case != cbr:decision some-case-base no-case and
    cbr:decision some-case-base yes-case != cbr:decision some-case-base reference-case) [
    report cbr:incmp
  ]
  if not is-list? yes-state or not is-list? no-state or not is-list? reference-state [
    report cbr:incmp
  ]
  if length yes-state != length no-state  [
    report cbr:incmp
  ]
  if length no-state != length reference-state [
    report cbr:incmp
  ]
  if (item 0 yes-state = item 0 no-state and
      item 1 yes-state = item 1 no-state and
      item 2 yes-state = item 2 no-state) [
    report cbr:eq
  ]

  let comparison-1-and-3 0
  foreach n-values (length yes-state) [i -> i] [ i ->
    if item i yes-state = item i reference-state [
      set comparison-1-and-3 comparison-1-and-3 + 1
    ]
  ]
  let comparison-2-and-3 0
  foreach n-values (length no-state) [i -> i] [ i ->
    if item i no-state = item i reference-state [
      set comparison-2-and-3 comparison-2-and-3 + 1
    ]
  ]
  if comparison-1-and-3 = 0 and comparison-2-and-3 = 0 [
    report cbr:incmp
  ]
  if comparison-1-and-3 > comparison-2-and-3 [
    report cbr:lt
  ]
  report cbr:gt
end

This example makes sure the decision is the same in all the matched cases as well. The defautl comparator does not do this.

Once this is implemented then it can loaded against a particular case base by using the command:

cbr:lambda new-comparator  

NETLOGO FEATURES

(interesting or unusual features of NetLogo that the model uses, particularly in the Code tab; or where workarounds were needed for missing features)

RELATED MODELS

achsium.nlogo uses this case base reasoner.

CREDITS AND REFERENCES

Author [email protected] (see https://gitlab.com/doug.salt/cbr for the repository). @