Relational Database Systems (RDBS) Part 1

Relational Database Systems (RDBS) Part 1


We’re going to focus on relational
databases because this model is what the databases that are widely used,
Oracle for example. The databases that are widely
used in real world, they actually use this relational model. So that’s one reason we’re
going to focus on it. It’s also been around and
investigated heavily and so on. So what does a relational database,
what’s the data model here? Well, a relational database consists
of what is called relations. Another name for relation is a table. Remember a table is basically,
it’s sort of like rows and columns. It’s a metrics kind of a structure. So relation is nothing but sort of
a table that has a bunch of columns, and bunch of rows. So what columns we have, what kind
of data items we’re going to have in the various columns,
in the database or in a relation. That’s defined by a schema,
that we have for that relation. A schema basically says
what each column is. And what is the nature of the data? Is it a name, it’s an address, it’s a
social security number, whatever it is. The columns defined by
what we call attributes. So the values that we
store in the various columns actually are attribute values. Think of about the schema defines what
these various columns of the table are or the various attributes are. And value for a given attribute
is the attribute value. We talked about columns or
attributes, but of course, then we have rows in a table. The given row is going
to contain value for each of the attributes as defined by
the schema that we’re talking about. So, it’s column, row, cell of a metrics
in our table basically has a value. So, these rows are called Tuples. So tuples basically, as I said, are attribute values that make
up that row of the table. And what these values are, again,
is defined by the schema that we have. It’s a table and the attribute values
and the rows are called tuples and things like that. Some of those attribute values are kind
of special, they’re called keys. The various types of keys, primary and
foreign, and stuff like that. But keys are basically values that you
uniquely define a given tuple or a role. So, if the database stores
information about eight employee there’s going to be a tuple for
each employee. Information about that employee is
going to be stored in the table or the relation given employees
information will define one tuple. And if you identify employees by,
let’s say, their social security number, then that’s going to be
the key value in that tuple. And it’s uniquely identifies the tuple
because social security numbers are different for different users.

Danny Hutson

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