An entity is one thing which can be distinctly identified.
Example:
It's a concept to abstractly group similar things.
An entity is a single occurrence of an entity set, it's also known as an instance
An entity would be represented:
An attribute is a descriptive property or characteristic of an entity.
The value about an entity is expressed by a set of attribute-value pairs
<math> \begin{array}{rrr} att1 & \mapsto & Foo \\ att2 & \mapsto & Blue \\ att3 & \mapsto & 20 \\ att4 & \mapsto & Sunny \\ \end{array} </math>
An id is attribute that describes the identity of an entity.
Entities are associated via relationship
A permanent entity is always part of the system, never entering or leaving.
A temporary entity is not always present in a system. It enters the system at some point in time, stays for a while, and then leaves again at some other point in time.
A transaction, a customer in a restaurant is an example of a temporary entity.
There is a constant flow of temporary entity.
An active entity (also known as dynamic model components) are entities that follow a process lifecycle (hence active and not passive).
Dimension are generally not an active component whereas a transaction is.
Asynchronous communication between entities is based on signal and reception