Hello world. I'm talking about entities and attributes those are two very important terms that we will be using.

in systems design and analysis.

Entities are the things in a system

That we keep data on.

Attributes are the properties, or information about the entities.

I'm taking a look at some information in the registration system.

You can see...

We have

courses and CRN,

Days and times.

No way to know that something is an entity is if you have information about that item.

For instance,

CMSC 243,

the course,

has a title.

It also has the number of credits.

It has prerequisites.

So course is one of our entities.

Next Saturday we have a CRN or section.

One of the ways you can tell that that is an entity also,

is because

Days Tuesday Thursday applies only to that one section.

Not to

all CMSC 243 courses.

Same with the  days, the time, the end date,

Number of seats available. So those are all attributes.

Refer to the section.

Whereas the title,

Prerequisites,

And the number of credits are attributes that refer to the course.

This one is a little hard to tell from here.

But the room is given as CS451.

Somewhere in our system, there is

Information about that room. For instance it may tell you.

What kind of equipment is available there? Does it have a smart instructor workstation? How many seats are in that room?

And some information like that.

So we can sort of imagine that there's going to be information about that room even though we don't see.

The next entity that we have here is the name of the instructor.

Janet Joy doesn't teach.

All computer science classes or all CMSC 243 classes.

The instructor refers just to that one section

that you see there.

Those are entities,

We have here: the course, the crn, the room, and the instructor.

And the attributes of the course are the title, the number of credits, prerequisites; the attributes of the crn are the Day and The Time.

That information. We have a student,.

And the attributes of a student would be the name and the ID.

We also have information saying that this student is in this class.

And so you might have.

For instance the students ID.

And.

The CRN to join those together. That's another another type of record that we will look at a little later on.

Here I have a bank statement.

And this is typical of many, many different kinds of statements you might receive.

We have a customer.

And we have an account number.

And then we have some transactions.

This is actually a statement and has a date and so there's information about the statement or attributes about that account.

And we have.

Information about.

Transaction.

So transactions, the statement itself, and the account are all entities. Attributes for instance of a transaction would be the date, who it was to, and the amount, and so on. And you will see this whether it's a bank statement or a phone bill a credit card statement a whole slew of things like that have those particular things if you can imagine.

One customer might have several Accounts at a bank, he might have a savings account and a checking account. A customer might have more than one phone number that they get bills for.

And we also have each statement that we get might have

0 or more transactions on that statement: maybe one month you didn't do anything to your bank account,it just sits there.

For instance or you didn't make any long-distance phone calls or make any purchases on that credit card.

So this is a whole class of information.

And so that's it with entities and attributes.