Documentation:Part 3 OCL: Derivation properties

An introduction to OCL - the object constraints language - by example. The session also introduce the new MDriven debugger and shows how to get instant results of modelling efforts. Learn more about percentage and other useful properties to operate and moderate your model properly.

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derivation properties

percentage property calculation in oc

random operator toDecimal operation

Raw subtitles text

Hi welcome back to Part3 of Ocl

let's say someone changes the requirements

all of a sudden, the fruit can be in

multiple bowls, so I should have changed

the cardinality of the inbowl

property, but then we need to add a

Association object and association class

called fruit part in this case

I also add a percentage property on it,

so I know how much of the fruit that's in

the fruit bowl and all of a sudden,

we have quite different problem

we need to be able to calculate depending on

how much of the total fruits that's

in the fruit bowl, so fruit.allinstances

but we also have the link end

so if we watched the innerlink name

so these are the names to the fruit part in the association

so we find that fruit part

so fruit.allinstances and fruit part the

percentage, so if we select this you

should see, ok,okay I have the fruit allinstances

but since I changed the model

so all the data I had before is gone

so I need to update it

ok let's add a new attribute, so that we

know how much of the fruit is in  bowls

since the fruit is one fruit hundred

percent it shouldn't be more than a hundred

so we have the fruit parts that

this fruit takes part in and the

percentage of that and we sum that together

yeah we need to reload the model had

some changes, saving those okay then

I want to, the fruit I want to assign a

value to the percentage one just use a

random value to get some spreading my

data, so this is issuing the ocl editor

tend to the percentage int32.random

there should be random operator

the max value is a hundred so anything

between 0 and a hundred, execute that on

this glass bowl, okay and on the plastic bowl

oh I add semicolon too much

ok so now we have some random value in

the percentage in the fruit part now

we can make some use in the derivation of

the weight of the contents of the fruit bowl

because this is currently not

correct just summing up the weight of the fruits

we need to consider the part

of the fruits that that we use

so we iterate over fruit part the percentage

then we divide that by hundred to get a

fraction and we multiply it with now we

can follow the single link back to fruitInBowl

and get the weight of the

of the whole fruit

and we need to sum that up but that

would be a double and we need an int 32

so we need first to convert it to a

decimal, because that's the highest

position and then we can take it to int32 like that

ok so now we fix that one

let's see how much is in the bowls

so are there any bowls that

oh I should use two errors in

this expression is no one meant I meant

first of all this is spelled like wrong

but what the type is, ok that's the error it was fruit bowl

should have been fruit

okay how much is using bowls, if its

larger than a hundred then that fruit is overused

so we could warn about this in

our application of course, now I have the weight of the

contents as actually and considering the

the percentage of the fruit that's in

there the bowl, let's see what's this then

adding a new derived attribute and

presentation and grab the type name

from the fruit that's in the single link

fruit bowl, that's not like that with

weight of and same thing here back to

the single link fruitInBowl weight

but we want to multiply it by our percentage

how much did we use

ok let's do this, we calculate the actual weight

in separate drived attribute

fruit inbowl, weight, times percentage

devided by hundred, to decimal, we need to go to decimal

because there's the conversion

to int32 is from decimal, ok it's the actual

weight now we have that and we can head back

yeah we have an error in

this expression presentation expression

because you can't just add int32 to a

string, we need to make it ok

and back to the debugger, re-read the model

check the fruit bowl hasn't change

that's because we haven't actually made

use of your presentation on the

fruit part, we're going to need to have

back to fruit bowl, in this one fruitinbowl presentation

that's not correct we should use the

fruit part of that, but we need to say

self in front of it, like so

reloading the model, now we can see that

we have detailed information about

what we actually have in the bowl and since

the weight of the contents now actually

is calculated in the fruit part for each

and the weight of each part is

calculated we might as well just sum

those up to reduced the need for definition

and like that doesn't change anything so

these are some examples on how you can

use ocl to navigate your data to

calculate your data to derive data

new information from your existing data and

there's loads of applications for

this and following these rules you can

actually complete the whole software

system only with business rules

expressed in icl, so hopefully

ypu will check out some of our other videos to

learn more about that, thank you for watching this Ocl introduction