In this video, I'm going to talk about 
the next form of data definiton, which is 
called an interval. 
So this is really just an example how to 
design data, and data driven templates 
problem. 
I've got the seat num starter file open 
and because this is a how to design data 
problem I'm going to put the how to 
design data definitions recipe here off 
to the right and over in my broswer 
window I've got the how to design data 
recipe page open. 
Back at the problem. 
So, imagine we're designing a program to 
manage ticket sales at a theater, and we 
want to represent the seat number in a 
row, and each row has 32 seats. 
So, it's kind of a boring theater. 
That's what this comment here means, it's 
a perfectly rectangular theater. 
And we need to represent a seat number. 
So if you think about that a row looks 
kind of like this, and the seat numbers 
can be something like one or two or 
three, all the way up to 32. 
Since these are seat numbers and not 
indexes in a string, let's use the normal 
kind of numbers that people like, where 
they start at one and go to 32. 
So the question is, that's the 
information, information is numbers from 
one to 32. 
That are going to be seat numbers. 
How are we going to represent that? 
Well, if we go over to the How to Design 
Data webpage, and again, this is a 
webpage that you should read ahead of 
time. 
I'm going to be using it kind of in a 
mode where I already know how to use it. 
I'm going to scroll down, to this table 
that says when the form of the 
information to be represented. 
Is atomic. 
Well this is atomic. 
Seat numbers are going to be something 
like one or two. 
And that's atomic. 
But I'm going to keep reading because 
sometimes there's something more 
specific. 
And here it is. 
When it's numbers within a certain range. 
And that's exactly what this case is. 
It's numbers like one, two, three all the 
way up to thirty two. 
So, it's numbers within a certain range. 
And there's a kind of data definition for 
that called an interval. 
So, here we go to intervals. 
Now, an interval type comment looks 
something like this. 
There's a type name and then we're going 
to say a kind of number and then a 
notation for talking about the range Let 
me jump back over here to Dr. 
Racket and do it and I'll talk about that 
notation as I go. 
So let's see, we're going to say 
something like, SeatNum is, and then 
these are numbers, integers. 
Between 1 and 32. 
And what's going with these square 
brackets is, in square brackets mean 
inclusive. 
So this means integer is starting at one, 
including one. 
Going up to 32 including 32. 
Let me just show you some variations on 
this so you'll understand all of what we 
can say. 
For one thing, this could be natural, 
because natural numbers are integers that 
start at, at 0. 
So I could say natural here. 
Natural one to 32, integer one to 32, 
they're the same. 
But some other variations. 
For example if I said something like 
number. 
132 and that's going to be a lot more 
things because numbers include real 
numbers, like 1.3 and 1.4 and 1.5 and we 
don't have that with seat numbers. 
We really need natural numbers or 
integers here. 
If I said natural square bracket 1 comma 
32 round bracket then that wouldn't 
include the 32 because the round bracket 
means up to but not included. 
So square means inclusive and round means 
not inclusive. 
So there we go. 
There's our type comment. 
Now I've got to say interpret this. 
So what's the interpretation here. 
Well lets see. 
These are seat numbers in a row and I 
might know some more information about 
that. 
In particular what I might know is that 
one and 32 are aisle seats. 
Or I might know something else about the 
theatre. 
But anything that would help me 
understand exactly what the numbers 132 
and all the numbers in between mean is 
what I would put in the interpretation. 
And now let me make some examples. 
I'll say seat number one and I'll just 
call that one. 
And seat number two might be 12. 
And seat number three might be 32. 
And the reasons we going to do multiple 
examples in this case. 
sometimes its nice to have examples that 
illustrate specific thing. 
So this might be an asile and this is a 
middle and this is an aisle. 
You always want to have at least one 
example and you should have other 
examples if they're illustrated, and 
again as I said when we were doing the 
city name data definition. 
As data definitions become richer, 
examples will become more important and 
more useful. 
So we got the type command the 
interpretation in the examples. 
Now we have to do the template. 
So I'll start the template like this 
define fn-for-seat-num, there is going to 
be some body there, and also inside the 
template process like this, like saying 
template rules used; now I am set to do 
the template I'll go back over here to 
the data definition page. 
I'll follow this link to the data-driven 
templates page. 
And now I've gotta look down and find 
this form of data, and interval. 
Intervals are atomic non-distinct. 
So we're going to end up using the same 
template rule here that we used For city 
name, which is just open parenthesis dot, 
dot, dot in the parameter name. 
So we go back here, we say, we say open 
parenthesis dot, dot, dot. 
The parameter name which is seat-num. 
And here we say, atomic non distinct and 
always like to put after the colon here, 
exactly what part the of type comment it 
was caused us to do that. 
You'll see it's starting in the next data 
definition we do. 
When data definitions gets more 
complicated, why we're doing that. 
There we go, that data definition is 
complete. 
I'm going do everything well formed. 
I'll put a comment like that there. 
So have a comment like that. 
And we're good to go.