INTERPRETING REQUIREMENTS - A Developer's Guide to Data Modeling for SQL Server - page 123

Entities Key Words
We look for nouns to help us find entities. Nouns are people, places, and
things. Most entities represent a collection of things, specifically physical
things that we work with. It is for this reason that nouns are a great identi-
fier of entities. Let's say a user tells you that the company has several sites
and each site has at least ten employees. You can use the nouns to start an
entity list; in this case, the nouns are site and employees. You have now de-
termined that you will need a Site and an Employee entity in the data model.
Attribute Key Words
Like entities, attributes are described as nouns, but the key difference is
that an attribute does not describe more than a single piece of data. For ex-
ample, if a customer describes a vehicle, you will likely want to know more
about the information he needs about the vehicle. When a customer de-
scribes the vehicle identification number (VIN) for a vehicle, there isn't
much more detail to be had. Vehicle is an entity, and VIN is an attribute.
When we look for attributes, we also need to look for applied owner-
ship of information. Words like own, have , contain , or belong are your
biggest clues that you might have a few attributes being described.
Ownership can describe a relationship when it's ownership between two
entities, so make sure you don't turn entities into attributes and vice versa.
Phrases like “Students have a unique student ID number” indicate that
students own student IDs, and hence a student ID is one attribute of a stu-
dent. You also need to look for phrases like, “For customers we track x, y,
and z.” Tracking something about an entity is often a flag that the some-
thing is an attribute.
Relationship Key Words
The same kinds of key words you looked for to determine attributes can
also apply to relationships. The key difference is that relationships show
ownership of other relationships. How do you tell the difference between
an attribute and a relationship? That is where a little experience and trial
and error play a big role. If I say, “An order has an order date and order
details,” I am implying that an order owns both an order date and order de-
tails. In other words, the order date is a single piece of information,
whereas order details present more questions about the data required for
the details; but both are part of an order.
Additionally, verbs can describe relationships between entities. Saying
that an employee processes an order describes a relationship between your
employee and your order entity.