Allow turtle moves around a specific patch - netlogo

I want to build a model of a city with hospitals. There are people, and people who are employees of specific hospital.
I want the employees to be moving without exceeding a maximum distance from the hospital where they work.
persons-own [
hospital-employees? ; true if work in hospital
hospital-position-cordx ; xcor of the hospital where he works
hospital-position-cordy ; ycor of the hospital where he works
]
to move
; they can move only around the hospital (max distance 5 patch)
ask persons with[hospital-employees?][
...........
]
; other people can move free
ask persons with[not hospital-employees?][
rt random 180
lt random 180
fd 1
]
end
It this possible?

I'm sure there are many ways to approach that problem. Here is a simple one:
breed [hospitals hospital]
breed [employees employee]
employees-own [my-hospital]
to setup
clear-all
set-default-shape hospitals "house"
set-default-shape employees "person"
ask n-of 5 patches [
sprout-hospitals 1 [
hatch-employees 5 [
set my-hospital myself
]
]
]
reset-ticks
end
to go
let max-distance 5
ask employees [
ifelse distance my-hospital > max-distance - 1 [
face my-hospital
] [
rt random 180
lt random 180
]
fd 1
]
end

Related

Stopping turtles from having negative resources

My model creates a relationship between employees and citizens. Whereby the employees obtain office and then distribute to the employees:
globals [
office-space
]
breed [ offices office ]
breed [ service-desks service-desk ]
breed [ employees employee ]
breed [ citizens citizen ]
offices-own [ money ]
employees-own [ money ]
citizens-own [ money ]
to setup
clear-all
create-offices 1 [
set shape "building institution"
set size 4
set color yellow
set money num-of-money
]
create-employees num-of-employees [
set shape "person"
set size 1.5
set color blue
setxy random-xcor random-ycor
]
create-citizens num-of-citizens [
set shape "person"
set size 1.5
set color white
setxy random-xcor random-ycor
]
;; create 4 service desks
let service-desk-patches (patch-set patch 0 8 patch 8 0 patch 0 -8 patch -8 0)
ask service-desk-patches [
sprout-service-desks 1 [
set shape "building institution"
set color pink
set size 3
]
]
;; create office space
set office-space patches with [pxcor <= 8 and pxcor >= -8 and pycor <= 8 and pycor >= -8 ]
ask office-space [set pcolor grey]
;; set all employees randomly within the grey box
place-on-color-employees
;; set all citizens randomly outside of the grey box
place-on-color-citizens
reset-ticks
end
to place-on-color-employees
let _patches (patches with [pcolor = grey])
ask employees [
move-to one-of (_patches with [not any? turtles-here])
]
end
to place-on-color-citizens
let _patches (patches with [pcolor = black])
ask citizens [
move-to one-of (_patches with [not any? turtles-here])
]
end
to go
ask employees [
set label money
]
ask citizens [
set label money
]
employee-movement-without-money
employee-take-money
employee-movement-with-money
citizens-movement
citizen-take-money
tick
end
to employee-movement-with-money
ask employees [
ifelse [ pcolor ] of patch-ahead 1 = black
[ rt random-float 360 ]
[ forward 1 ]
let target min-one-of citizens [ distance myself ]
if money > 0 [
face target
fd 1
]
]
end
to employee-movement-without-money
ask employees [
let target patch 0 0
if ( money = 0 ) or ( money < 0 ) [
face target
fd 1
]
]
end
to citizens-movement
ask citizens [
ifelse [pcolor] of patch-ahead 1 = grey
[ rt random-float 360 ]
[ forward 1 ]
let target min-one-of service-desks [ distance myself ]
if money = 0 [
set heading (towards target )
]
]
end
to employee-take-money
ask employees [
if any? offices-here [
set money money + 1
set color green
;set label money
]
]
end
to citizen-take-money
ask citizens [
if any? employees in-radius 0.5 [
ask employees [
set money money - 1
]
]
set money money + 1
set color orange
]
end
When this model is run, the employees collect money and go to meet citizens, however, in the citizen-take-money procedure, I have not found a way to prevent the citizens from taking money from the employees so they don't have negative values. I tried adding the employee-movement-without-money to force the employees to turn move away from the citizens, but they just congregate on patch 0 0.
I also tried adjusting the citizens-take-money procedures by creating an if and arugment:
to citizen-take-money
ask citizens [
if (any? employees in-radius 0.5) and (employees money > 0) [
ask employees [
set money money - 1
]
]
set money money + 1
set color orange
]
end
But that didn't work either.
First piece of advice, build NetLogo models gradually. You need to make sure each piece works before adding the slightly more complicated behaviour. You should never have more than one thing wrong in a NetLogo model at the same time, very hard to debug.
Here, the basic problem appears to be that you are acting on all turtles instead of just the relevant turtle. Here is your supplementary code that tries to introduce a check:
to citizen-take-money
ask citizens [
if (any? employees in-radius 0.5) and (employees money > 0) [
ask employees [
set money money - 1
]
]
set money money + 1
set color orange
]
end
First, have a look at your check - conceptually, what are you testing with the second part employees money > 0. That doesn't actually look like valid NetLogo code to me, are you trying to ask if there are any employees with with money > 0?
Regardless, let's say it gets past that check, the next line is ask employees - at this point you are telling EVERY employee in the model to reduce their money.
What you need to do is just find the right employees and have those ones reduce their money. Something more like:
to citizen-take-money
ask citizens
[ let nearby employees in-radius 0.5 with [money > 0]
if any? nearby
[ ask nearby [ set money money - 1 ]
set money money + 1
set color orange
]
]
end
Also, this procedure is asking every citizen to do this and you have named it as if only one citizen is doing it. So think about which way you actually want the process to work.
Finally, what happens if you have several citizens close to several employees. Say 3 citizens reduce their money because they are close to the same employee - at the moment, the employee only increases their money by 1 and the remaining 2 disappears. This is an example of what I mean by build gradually and check it works before adding in the next thing. Perhaps you could have them just change colours if the condition is met before trying to add in the money transfers. That would help you spot that you had lots of people triggered at once.

Creating conditional links between two breeds

I am writing a NetLogo model of a housing market and its political ramifications. There are two breeds in the model: households and houses. An early step in my development with which I am having difficulty is having households match to houses via one of two types of links, own or rent, defined by nested conditional statements. This has resulted in two difficulties I haven't been able to overcome as of yet.
Within the command setup-market command, I'm trying to define a set of possible houses to purchase for each household which, if they meet a set of conditions, the household then buys (and creates a link). If it cannot afford to buy, then it will try to rent. If it cannot afford to rent the household will die.
My code continually results in the following error:
IFELSE expected input to be a TRUE/FALSE but got the turtle (house XXX) instead.
There is a further issue I'm having as well later in the code (in the two lines commented out with ";") where I attempt to set the variables owner-occupied and renter to 1 based on the presence of the appropriate link (they should remain 0 and the household should die if it remains unlinked).
The full code is below. The line with ";; This is the line giving me trouble" denotes where the error seems to be occurring.
UPDATE:
Code has been updated with JenB's solution. Resulting error is now:
CREATE-LINK-WITH expected input to be a turtle but got NOBODY instead. which occurs at the line: create-link-with one-of potentialHomes [ set color red
undirected-link-breed [own-links own-link]
undirected-link-breed [rent-links rent-link]
breed [city-centers city-center]
breed [households household]
households-own
[
age
money
income
monthly-income
consumption
monthly-consumption
hh-size race
preference
net-income
net-monthly-income
myHouse
]
breed [houses house]
houses-own
[
cost
down-payment
mortgage-payment
rent
rent-premium
rooms
onMarket
owner-occupied
rental
onMarket?
]
patches-own [
seed? ;;district seed
district ;;district number
full? ;;is the district at capacity?
quadrant
]
to setup
clear-all
reset-ticks
setup-patches
set-default-shape households "person"
create-households num-households [ setxy random-xcor random-ycor ]
set-default-shape houses "house"
create-houses num-houses [ setxy random-xcor random-ycor ]
setup-households
setup-houses
setup-market
generate-cities
end
to generate-cities
let center-x random-xcor / 1.5 ;;keep cities away from edges
let center-y random-ycor / 1.5
end
to setup-patches
ask patches with [pxcor > 0 and pycor > 0] [set quadrant 1 set pcolor 19 ]
ask patches with [pxcor > 0 and pycor < 0] [set quadrant 2 set pcolor 49 ]
ask patches with [pxcor < 0 and pycor < 0] [set quadrant 3 set pcolor 139 ]
ask patches with [pxcor < 0 and pycor > 0] [set quadrant 4 set pcolor 89 ]
end
to setup-households
ask households
[ set age random-poisson 38
set money random-exponential 30600
set income random-exponential 64324
set monthly-income income / 12
set consumption .5 * income
set monthly-consumption consumption / 12
set hh-size random 6 + 1
set net-income income - consumption
set net-monthly-income monthly-income - monthly-consumption
]
end
to setup-houses
ask houses
[ set cost random-normal 300000 50000
set down-payment cost * down-payment-rate
set mortgage-payment (cost - down-payment) / 360
set rooms random-exponential 3
set onMarket 1
set rent mortgage-payment + mortgage-payment * .25
set owner-occupied 0
set rental 0
]
end
to setup-market
ask houses
[ set onMarket? TRUE ]
ask households
[ ifelse any? houses with [ [money] of myself > down-payment and [net-monthly-income] of myself > mortgage-payment ]
[ let potentialHomes houses with [[money] of myself > cost and onMarket? ]
create-link-with one-of potentialHomes [
set color red
]
]
[
ifelse any? houses with [ [net-monthly-income] of myself > rent]
[ let potentialRentals houses with [ [net-monthly-income] of myself > rent and onMarket? ]
create-link-with one-of potentialRentals [ set color blue ]
]
[ die ]
]
]
ask houses
[ if any? link-neighbors [set onMarket FALSE ]
;if any? link-neighbors and color red [ set owner-occupied 1 ]
;if any? link-neighbors and color blue [ set rental 1 ]
]
end
to go
move-households
tick
end
to move-households
ask households [
move-to myHouse
]
end
You don't need to "suspect" where the problem is, NetLogo points to the problem line. Running your code, the problem is actually ifelse one-of houses with [ [net-monthly-income] of myself > rent]. Looking at that line, you pull out a randomly selected house from the pool with rent less than income. But you don't have a condition for the ifelse to test.
In previous constructions you have had != nobody at the end but you forgot that in this line. That will fix the error, but your code would be much less error prone if you used any? instead. You seem to be using one-of .... != nobody to test whether there are any turtles that satisfy the condition. That's what any? is for.
So instead of:
ifelse one-of houses with [ [net-monthly-income] of myself > rent] != nobody
[ let potentialRentals houses with [[money] of myself > rent and onMarket = 1 ]
create-link-with one-of potentialRentals [ set color blue ]
]
[ die ]
you can have:
ifelse any? houses with [ [net-monthly-income] of myself > rent]
[ let potentialRentals houses with [[money] of myself > rent and onMarket = 1 ]
create-link-with one-of potentialRentals [ set color blue ]
]
[ die ]
I should add that there is a potential logic problem here. Say there are houses with rent lower than income, the code goes to the first (true) actions. But there's no guarantee that there are any houses that satisfy the new conditions, which are different.
Also, NetLogo has the concept of true and false so you don't need to use 1 and 0. By convention (but not required), boolean variable names end with a question mark. So you could have set onMarket? true instead of set onMarket 1. Why would you do this? It makes logical operators cleaner and easier to read (which reduces bugs). Your line:
let potentialRentals houses with [[money] of myself > rent and onMarket = 1 ]
would look like:
let potentialRentals houses with [[money] of myself > rent and onMarket? ]
And you can do things like if not onMarket? instead of if onMarket? = false or if onMarket = 0

Netlogo: How to ask link-neighbor to do something

I am simulating a classroom. In a classroom there are about 90 seats, 20 lights, 20 fans and 4 ACs. I create num-of-students where each student has an assigned random entry-time. When each student enters after a random time and sits on a seat the corresponding (in-radius)light or fan or ac turn on and a link is established between the the student and the in-radius appliance. Each appliance (e,g light, fan and AC) has their own wattage value. After all the students sits down the total energy consumption (in KWh) will be calculated for all the fans, lights and ACs.
How can I store the on-time of each appliance e.g (time minus entry-time), where time is the total class time. So that afterwards I can sum all the on-time of each appliance(e.g fan) and multiply it with its watt value. This is the part of the code.
globals[
temp1 simulation-timer number-of-seats number-of-lights number-
of-fans number-of-acs ]
breed [lights light]
breed [fans fan]
breed [acs ac ]
breed [students student ]
to setup
...
...
place-seats-students
place-lights
place-fans
place-acs
create-students-classroom
end
to create-students-classroom
create-students number-of-students [
set entry-time random threshold + 1
let stu-no sort-on [who] students
foreach stu-no [x -> ask x [ show (word x " -> " entry-time )
] ]
ask students [
set shape "person"
set color 3
] ]
end
to go
set simulation-timer 0
output-show (word "timer = "simulation-timer )
tick
move-students
while [simulation-timer < time ] [
set simulation-timer simulation-timer + 1
output-show (word "timer = "simulation-timer )
end
to move-students
let s sort [who] of seats
let a first s
let l length s
while [ l > (number-of-seats - number-of-students )] [
set temp1 simulation-timer
tick
tick
ask students [ if ( entry-time = temp1 ) [
move-to seat a
set color red
ask students
[create-links-with lights in-radius 5
create-links-with fans in-radius 5
create-links-with acs in-radius 9 ]
show (word "number of links is" count links)
appliance-on
store-on-time
show (word temp1 "," l "," a)
set s remove a s
set a a + 1
set l length s
]
]
set simulation-timer simulation-timer + 1
output-show (word "timer = "simulation-timer )]
end
to appliance-on
ask students with [color = red ]
[ask my-links
[ask other-end [set color green] ] ]
stop
end
to store-on-time
ask students [
ask link-neighbor fan ifelse it is on [
let on-time [ time - entry-time ]
[do nothing]
ask students [
ask link-neighbor light ifelse it is on [
let on-time [ time - entry-time ]
[do nothing]
end
How can I write the store-on-time procedure, so that later I will be able sum to all the on-times for all the appliance to calculate the KWh consumed. Any help will be greatly appreciated.
If you need to store something, then you need to create a variable for it. Since they might turn on, off, on etc, I would personally have two variables for each appliance (eg lights-own and fans-own etc). For lights, they could be named light-on-time, light-on-duration and similarly for others.
The way this works in code is add
set light-on-time ticks
whenever you turn the light on. And have
set light-on-duration light-on-duration + ticks - light-on-time + 1
whenever you turn the light off. The reporter ticks is just the current state of the clock.

Subtract. SET variableX-variableY only once

I'm trying to set a resource variable. It will be time and will function like sugar in sugarscape. Its setup is: ask agentes [set time random-in-range 1 6].
The thing is... I want the agentesto participate in activities linking like we said here. But, with each participation, it should subtract a unity of agentes's time. I imagine it must be with foreachbut I seem to be unable to grasp how this works.
ask n-of n-to-link agentes with [n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
while [time >= 2] [
create-participation-with myself [ set color [color] of myself ] ]
foreach (command I don't know)[
set time time - count participations]]
Essentially, I want the agentes to look if they have time to participate. If they do, they create the link and subtract 1 to their time. Only ONE per participation. If they have 3 time, they'll have 2 participations and 1 time. If they have 1 time, they won't have links at all.
EDIT
You're right. I don't need while. About foreach, every place I looked said the same thing but I can't think of other way. About colors, they're only for show purpose.
The relationship between time and participation counts is as follows: the agentes have time they can spend in activities. They participate if time>=2. But every participation (link with activity) consumes 1 time when the link is active (I didn't write the decay code yet; they'll regain their time when it is off).
EDIT V2
Nothing, it keeps subtracting even with the []. Maybe the best choice is if I give you the code so you can try it. You'll have to set 5 sliders: prob-female (53%), initial-people (around 200), num-activity (around 20), n-capacity (around 25) and sight-radius (around 7). And two buttons, setup and go. I also set a patch size of 10 with 30 max-pxcor and max-pycor. Here is the code. Sorry if I'm not clear enough!
undirected-link-breed [participations participation]
turtles-own [
n-t-activity
]
breed [activities activity]
activities-own [
t-culture-tags
shared-culture
]
breed [agentes agente]
agentes-own [
gender
time
culture-tags
shared-culture
]
to setup
clear-all
setup-world
setup-people-quotes
setup-activities
reset-ticks
END
to setup-world
ask patches [set pcolor white]
END
to setup-people-quotes
let quote (prob-female / 100 * initial-people)
create-agentes initial-people
[ while [any? other turtles-here ]
[ setxy random-xcor random-ycor ]
set gender "male" set color black
]
ask n-of quote agentes
[ set gender "female" set color blue
]
ask agentes [
set culture-tags n-values 11 [random 2]
set shared-culture (filter [ i -> i = 0 ] culture-tags)
]
ask agentes [
set time random-in-range 1 6
]
ask agentes [
assign-n-t-activity
]
END
to setup-activities
create-activities num-activity [
set shape "box"
set size 2
set xcor random-xcor
set ycor random-ycor
ask activities [
set t-culture-tags n-values 11 [random 2]
set shared-culture (filter [i -> i = 0] t-culture-tags)
]
ask activities [
assign-n-t-activity]
]
END
to assign-n-t-activity
if length shared-culture <= 4 [
set n-t-activity ["red"]
set color red
]
if length shared-culture = 5 [
set n-t-activity ["green"]
set color green
]
if length shared-culture = 6 [
set n-t-activity ["green"]
set color green
]
if length shared-culture >= 7 [
set n-t-activity ["black"]
set color black
]
END
to go
move-agentes
participate
tick
end
to move-agentes
ask agentes [
if time >= 2 [
rt random 40
lt random 40
fd 0.3
]
]
end
to participate
ask activities [
if count my-links < n-capacity [
let n-to-link ( n-capacity - count my-links)
let n-agentes-in-radius count (
agentes with [
n-t-activity = [n-t-activity] of myself ] in-radius sight-radius)
if n-agentes-in-radius < n-to-link [
set n-to-link n-agentes-in-radius
]
ask n-of n-to-link agentes with [
n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
if time >= 2 [
create-participation-with myself [
set color [color] of myself ]
ask agentes [set time time - count my-participations] ]
]
ask activities [
if not any? agentes in-radius sight-radius [
ask participations [die]
]
]
]
]
end
to-report random-in-range [low high]
report low + random (high - low + 1)
END
EDIT V3
I asked Bill Rand to help me and he solved the problem. The issue was in this line: let candidates agentes with [ n-t-activity = [n-t-activity] of myself ] in-radius sight-radius. He solved the problem this way: let candidates agentes with [ n-t-activity = [n-t-activity] of myself and not participation-neighbor? myself ] in-radius sight-radius. Being this and not participation-neighbor? myself the condition to make sure that the agente is not already a part of that activity.
You almost never need foreach in NetLogo. If you find yourself thinking you need foreach, your immediate reaction should be that you need ask. In particular, if you are iterating through a group of agents, this is what ask does and you should only be using foreach when you need to iterate through a list (and that list should be something other than agents). Looking at your code, you probably don't want the while loop either.
UPDATED FOR COMMENTS and code - you definitely do not need while or foreach.
Your problem is the following code. You ask agentes that satisfy your conditions to create the links, but then you ask ALL AGENTES to change their time (line I have marked), not just the agentes that are creating participation links.
ask n-of n-to-link agentes with [
n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
if time >= 2 [
create-participation-with myself [
set color [color] of myself ]
ask agentes [set time time - count my-participations] ] ; THIS LINE
]
The following code fixes this problem. I have also done something else to simplify reading and also make the code more efficient - I created an agentset (called candidates) of the agentes that satisfy the conditions. In this code, the candidates set is only created once (for each activity) instead of twice (for each activity) because you are creating it to count it and then creating it again to use for participation link generation.
to participate
ask activities
[ if count my-links < n-capacity
[ let candidates agentes with [
n-t-activity = [n-t-activity] of myself ] in-radius sight-radius
let n-to-link min (list (n-capacity - count my-links) (count candidates ) )
ask n-of n-to-link candidates
[ if time >= 2
[ create-participation-with myself [ set color [color] of myself ]
set time time - count my-participations ] ; REPLACED WITH THIS LINE
]
ask activities [
if not any? agentes in-radius sight-radius [
ask participations [die]
]
]
]
]
end

Controlling lives of turtles in NetLogo

For a project, I'm developping a simulation in NetLogo dealing with rabies diseases in dogs and humans. I have some turtles-humans with dogs that can be vaccinated or not. At the beginning I create a dog with rabie and, in according to the fase (1 or 2) of the disease, it can spread the disease to other dogs with a probability. At the end the dog can die either for paralysis (if a probability is higher than 75%) or for other complications. Here's the code:
http://pastebin.com/esR75G3T
In the end you can see that a dog not dying for paralysis will die after some days (between 4 or 6). In other words when the days_infected are equal to end-life.
To check if everything is ok at the beginning I tried to set that NONE of the dog is vaccinated so everyone is supposed to get the disease. In fact when the dog is in phase 2 it will bite anyone. The problem is that if I delete the last line of the code, everything works and some dogs die of paralysis and the other remain alive. If I enable also the last line to let the other dogs die too, nothing works...no dog is infected. why?
This is not a problem with your code: this is a problem with the dynamics of your model. What's happening is that your initial sick dog dies before actually infecting another dog. This is why removing the if (days_infected = end-life) [die] "fixes" the problem.
When I tried your model with a huge population (e.g., 5000 people) so that encounters are more frequent, the infection does spread. You could also increase the probability of infection, or increase the duration of the "furious" phase, I guess.
Another unrelated suggestion, if I may: you should have distinct persons and dogs breeds. Trying to cram everything inside regular turtles makes your code much more complicated than it should be. The way I would approach this would be to create a link from the person to her dog, and then use tie so that the dog is automatically moved when you move the person.
Edit:
OK, here is a version of your code slightly modified to use breeds:
globals [
total_dogs_infected
total_dogs
dead_humans
dead_dogs
]
breed [ persons person ]
persons-own [
sick?
]
breed [ dogs dog ]
dogs-own [
sick?
vaccinated?
rabies_phase
days_infected
end-incubator
end-furious
end-life
]
to setup
clear-all
initialize-globals
setup-turtles
reset-ticks
end
to initialize-globals
set dead_humans 0
set dead_dogs 0
set total_dogs_infected 0
end
to setup-turtles
set-default-shape persons "person"
set-default-shape dogs "wolf"
create-persons people [
setxy random-xcor random-ycor
set size 1.5
set sick? false
ifelse random 100 < 43 [
set color green
hatch-dogs 1 [
set color brown
set heading 115 fd 1
create-link-from myself [ tie ]
set days_infected 0
set vaccinated? (random 100 > %_not_vaccinated)
if not vaccinated? [ set color orange ]
]
]
[
set color blue ;umano sano senza cane
]
]
set total_dogs count dogs
ask one-of dogs [ get_sick ]
end
to get_sick
set sick? true
set color white
set rabies_phase 1
set end-incubator 14 + random 57
set end-furious (end-incubator + random 5)
set end-life (end-furious + 4 + random 2)
set total_dogs_infected total_dogs_infected + 1
end
to go
move
infect
get-older-sick-dog
tick
end
to move
ask persons [
rt random 180
lt random 180
fd 1
]
end
to infect
ask dogs with [ sick? ] [
if (rabies_phase = 1 and (random 100) <= 2) or rabies_phase = 2 [
ask other dogs-here with [ not sick? and not vaccinated? ] [ get_sick ]
]
]
end
to get-older-sick-dog
ask dogs with [ sick? ] [
set days_infected days_infected + 1
;the incubator phase ends after at least 14 days + random(57) and then we have phase 2 (furious)
if (days_infected = end-incubator) [ set rabies_phase 2 ]
;when the main furious phase finishes we have 75% of probability that a secondary furious phase continues for other 4 - 6 days until death ;or we have a probability of 25% that the disease end in paralysis with a fast death
if (days_infected = end-furious and (random 100 > 75)) [
set dead_dogs dead_dogs + 1
die
]
if (days_infected = end-life) [
die
]
]
end
; These last reporters are not used,
; they just illustrate how to get the
; dog from the owner or vice-versa:
to-report my-dog ; person reporter
report one-of out-link-neighbors
end
to-report has-dog? ; person reporter
report any? out-link-neighbors
end
to-report my-owner ; dog reporter
report one-of in-link-neighbors
end
Not only does it simplify some expressions (e.g., ask dogs with [ sick? ] instead of ask turtles with [ has_dog? and sick_dog? ]), it opens up all sorts of possibilities: a dog could run away from its owner, the owner could die without the dog dying, an owner could have two dogs, etc.