Specific items of data can be addressed conveniently if three attributes are provided. These are represented in SQL by the table name, column names and id. (The id is not usually specified directly in an SQL query, and when it is it is specified as another column name.)
In this wiki, I will nearly always use entity name for table name, attribute names for column names, and instance name for id. (Although I am considering changing the term entity to the term collection. Everything is a part of a collection of none, one or many things)
If you don't know SQL, then this is how I would explain it.
When thinking about data, the current data in hand whatever that may be, we can think of it as a member of an entity by answering the question "What is it?".
(Of course we rarely ask ourselves the question "What is it" of everyday objects, we just know what it is)
The answer is (nearly) always easy. We always know what we are holding, using, thinking about. If I am holding a radio, I know it's a radio. Automatically I identify it as a member of the collection of radios.
The radio I have in mind is mine. It is a complete individual member of the radios collection. It is unique - it is right here now. Whether or not I know its instance name, it has a name in the full set of radios ever built, and yet to be built. Implicitly the radio has an instance name within the collection of radios.
I don't care what the instance name for this radio is within all radios. But I have two radios. So I do assign a name to this radio - this is the working radio, the other is the broken radio. For my own needs of the radios entity, the instance names which would fully define my radios are working and broken. If I were to get another radio it would be the digital radio. Now my radios would be -
Working
Broken
Digital
Three instances of radio.
Each of these radios share attributes. Attributes like size, weight, colour, power source, outputs, tuners, transmitters, receivers.
Data is defined by
entity name
The name given to the collection of data.
A collection of invoices would probably be called invoices. Invoices would be the entity name of the collection of invoices.
attribute names
The names given to the attribute values stored in each instance of an entity.
instance name
The name given to the particular instance of the entity.
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