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. This particular session explains the configuration of different operator, concept of derivation and principles of various ocl associaton tools by practical example . It's as closely clear and understanble to learn and to be taught with.

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This part includes overview on:

code comments associations temporary variables introduction (temp operator) add operator at(0) operator derivation asCommaList operator if operator groupby operator sum operator add criteria to the grouping adding a variables m1, m2, m3 collections Collection operators
symmetric difference operator difference operator

Raw subtitles text

I welcome back this is session two of

the ocl expressions extending the model

with a fruit bowl, given it a property

name and then this is also new that you

when you enter code comments on

classes, you will have access to them

in the ocl editor, so this will help you

as your model grows to know what is what

so in the ocl editor, whenever you edit something and you point at it

it says the code comments, so that's a new thing

ok and the fruit bowl, it's supposed to contain fruit

toggle square line to ensure that

Association line is always squared

going to give the association ends better names

than the defaults and this is the multiplicity and

it's 0 to many and in the other end

it's 0 to 1, so the fruit can be in one bowl and bowl

can contain many fruits, that's either in orange or an apple

so re-reading the model

create a bowl and this is a way to, in ocl,

to introduce temporary variables

let's make it easier for you to set

multiple properties just showing you for

this is the purpose of this video so

let the let operator temp is a temporary variable from both create in

and then you can use the temporiable

you can set the property, so this is one

expression that creates and sets the

property in one goal

going to create another one plastic bowl

one glass bowl and one plastic bowl

there we have them, first I'm going to work on the glass

bowl, it's a collection of fruit bowl, but I

just one to one, so I say first.FruitinBowl

that's the collection of fruit I want to

add fruit, add operator

so now I need to find a fruit

fruit.all instances, but that's a collection of fruit

I need one fruit to add I used to at(0)

operator again, grabing a zero fruit

the first fruit and then I change

this to add another fruit

and then I would be able to see rather

in the glass bowl the fruit in bold

I see I have three fruits, two oranges and

one apple, ok and let's add an attribute that states

what it contains, contains this fruit to

make that derived and the derivation

should be fruit in bowl presentation but

that will be a collection of string, we

need a single string and there's an

operator asCommaList simply takes a list

of strings and sets a comma between each

re-read the model like that "contains this fruit"

that's the glass bowl, but ocl also has an "if" operator, so

let's see if the fruit in bowl is empty

then we return the string "no fruit at all"

else wereturn the one we just constructed

and if ,it's important to end your

expression, and both parts of the

expression must return the same type in

this case a string, so if we look at all

the fruit bowls, we can spell all

instances correct,  we see that the glass bowl

has fruits and the plastic bowl has

no fruit at all, but if I were to add

fruit to the glass bowl, the derived

property would get another apple in this

case undo that, we do under so fully

subscribe and what if we were to add one to the plastic bowl

now we'll see a important principle that

our model states that the fruit can only

be in one bowl at a time, so

adding it to get up on the bowl to the

plastic bowl, actually removes it from

the glass bowl, this is of course obvious

but not so obvious when programming

against databases etc

modeling really helps us to work in high level of

abstraction to do things right

just to say supposed to be straightaway

avoiding a lot of simple mistakes w

we have a groupby operator in ocl, that we

can use to certain things

let's see how it works, if you have a

collection of something you can collect

over it and state what you want to group

by what's the unique property that you

want to isolate and keep and sort,

to group the other items by, so I want to

order by the type, ocl typename, but wait

a minute this wasn't what I expected

it's a string, I wrote the wrong thing I

wrote the property contains this fruit

when I intended to write the association fruit in bowl

so now I have first, part one that will

contain the type name and then a list a

list of the ones that are of the type, so

then we can continue and use to result

can collect and get the presentation of each fruit in the list,

yeah since the list contains many it

will be a collection of

no, actually, that the list needs to have...

it needs to, its case sensitive

the property was named list with the big L

you need to get that, like this,

asCommaList to reduce the collection of

strings, to a simple string, ok so

and now we have grouped the fruits in

the bowl and oranges on one end and a

apples on the other end and when we

remove or move the fruit we will see the effect

and let's copy that and do and yet

another tuple part, summing up the weights

there is an ocl operator sum

that just adds up all the numbers and

let's elaborate a bit on what to write

so the orange weight sums up to 43 grams

the apple weight sums up to 21 grams

but the groupby only chcks on type

name, what we can do is also add another

criteria to the grouping and that would

be what bowl the fruit is in

like that, so now we know what bowl

the fruit is in and we could use that

information in our text presentation

the tool tuple +x and there's a new part

of the tuple, but wait a minute

it's not called part2 since this is a

strict model name InBowl, we can use that

when we create a tuple, so that's

used, so this expression it's rather harry

but then if we remove the criteria

to only check the glass bowl we will see

that the use of it, now we sum up and see

that the plastic bowl has the weight of 23 grams

let's set another derived

attribute on the fruit bowl

summing up the the weight of the

contents, derived, derivation ocl

should grab the fruit in the

bowl, the weight and the operator sum

so re-reading the model

we see the weight of the contents and we

see contains this fruit, etc

if we add a move fruit the things update

in there debugger you can add your own

variables to make it easier for you to do things

let's add a variable for the glass bowl

and another one for the plastic bowl

so this is the name of the variable, colon,

the type of the variable, then action you can

there are three collections

m1 m2 and m3 that you can easily assign to

from the selected things in the

result list, so this will give you a good

way to access specific objects, so let's

see if I manage to assign the glass bowl

to m1 and then the plastic bowl to m2,

which I selected, like that

these are actually collections of one

no, there are objects, sorry

so the glass bowl is of type "fruit

bowl" so it has property contains this fruit

and you can follow the associations, ocl

editor is acting up them I'm taking

I'm taking notes to fix these after I've done this presentation

so what I really want to do now is to show you some of the

operators that work on collections

so we have the union of

course, we saw that before and

we also have an operator called intersection

that use fo from time-to-time

intersection is, well it's the intersection between

two collections, so what equals the two collections

what thing is in both, so if I do the

glass bowl and a collection with orange all instances

I will get all oranges in the glass bowl, fruit all instances will

of course return all the contents of the

glass bow,l because there's nothing else than fruit in it

another operator symmetric difference

the sets contain and contain all the elements that are

in set two, and set one and set two, but not in both

so this will be the all the fruits that aren't assigned any fruit bowl all the apples

so and I want you to get to know these

operators as they will help you to

express yourself and to get the business

rules, that you're after in an efficient manner

yet another operator is the difference

it's like the symmetric difference but

it's trickier, because it's not symmetric

so you need to take care of what

collection you put aware, so if you flip this around

you will get another very different result the collection one and

the collection two that is, so again just try them out

it's easy to to do in the debugger and

then I will close this session and get

right back with the third part