Hi. My name's Bear, and
today we'll be learning all about Entity Relationship
Diagrams or ERDs. We'll start off with
a high level overview, and then we'll dive in
and create one together complete with Entities, Attributes, Relationships,
and Cardinalities. By the end of this video,
you'll be able to create an entire ERD from scratch. Have you ever wondered why
you get error message telling you that your ideal social media
handles already been taken? Or, maybe you're curious how an
online store like Amazon keeps track of so many
different orders, customers, and products. The answer to these questions lies
within the creation of a database. A database is a
collection of information that's organized for easy storage, management,
updates, and retrieval. As you can imagine, there's a lot of moving
information in a database and understanding how each of these
elements interacts with one another can be
difficult to grasp. ERDs provide engineers with a
visual way to understand how this information is related
and how it works together. So, we make one? Today, I'm gonna be using
Lucidchart, and you can too for free, actually. By clicking
on the top right corner, you can access Lucidchart's
website, enter your email address, and have a free
account in just a few seconds. That way you can follow along
with me and create your own ERDs in the future. Okay. So in order to build ERD, we need to better
understand its individual components. And this starts with entities. An
entity is an object, like a person, place, or thing,
that's tracked in the database. For example, if we were to
buy something on Amazon, say a rockin pair of Crocs, "These aren't the droids
we're looking for." An entity could be the
customer, the order, and of course our Crocs, the product. Now, each of these entities
will have attributes, which are properties or
traits. In this case, under the customer entity, we
have customer ID, first name, last name, street, city, zip, and phone. It's important to note that
entities in your database will always be depicted as rows
and that attributes will always be depicted as columns. And now that we have these
different entities and attributes on the screen here, we can talk about the
relationships that exist between them. Relationships describe how
these entities will interact with each other. So when I
draw a line between these particular elements, I'm showing that there's some
sort of interaction or connection. And now that we
have our relationships in place, we'll see an interesting
notation attached to our lines. This is called cardinality. Cardalities help define the
relationship in a numerical context. Particularly within
minimums and maximums. For example, this list shows some
of the different cardinalities that can appear in an ERD. We
have one, many, one and only one, zero or one, one
or many, and zero or many. And if this isn't
making sense yet, don't worry. We'll walk through a
few examples to help piece everything together. Let's start by talking
about the relationship and cardinality that exists
between customer and order. The best way to do this is
to think about it logically. So we should ask
ourselves two questions. What is the minimum number
of orders that a customer could have? And two, what is the
maximum number of orders that a customer could have? Well,
a customer could exist, but he or she could have
zero orders. So to show that, will have that zero sign. Now we need to think
about the maximum. And as you've probably assumed, a customer could have
an infinite number of orders, especially when
it comes to Crocs. You can never have just one
pair. So to show that, we'll use this zero or mini
crows foot notation. Now, let's talk about the minimum
and maximum relationship between orders and customers. We'll start by applying
the same logic. So we'll ask ourselves what
is the minimum amount of customers that an order may have. And what's the maximum amount of
customers that an order may have? A specific order can have
one and only one customer. Imagine the confusion that
would come if the same specific order had a lot of customers.
So in this case, there can be one and only one number of
customers to order. And we show that using this sign here. Now let's talk about the
relationship or cardinality between orders and products. We'll ask ourselves
a similar question. A certain order can
have how many products? Well, for an order to exist,
it has to have one product, but a lot of different products
can be part of that order. So to show that in our diagram,
we'll change this notation. Now we'll ask ourselves
that question in reverse. A product can be a part
of how many orders. Well, a product could be a part of
no orders, but it could also be a product of many orders. So
we're going to use this zero or mini notation on our diagram.
And just like that, we've built an entire entity
relationship diagram. And even though it's
a simple example, you should now have the basic
skills needed to build a complex one. And not only that, but because you
used Lucidchart, you also have the option to
export this diagram directly into a database. Using the export feature, boosted chart can automatically
generate code that can be imported into the database
management system that you're using, helping you be
more efficient than ever. As always, thanks for watching. And be sure to check out
our next video where we dive into the complexities of ERDs
by discussing things like Primary keys, Foreign keys,
and Bridge tables. And if you're interested
in learning more ways Lucidchart can help you visualize
your data, check out training.lucid.co
Hope to see you there!
