Re: Entities - what are they?

1. No, an entity need not be represented by a table, nor need a table refer to an entity (although they often do).
2. Strictly, an entity is a business *object* and the borrowings would be a business *process* rather than an entity.
3. The transactions (borrowings) should be recorded as a table, but the contents refer to transient data that may be removed at your own timescale. Entity data is *required* as long as transactions refer to it and cannot be removed (it should always be *archived*).
4. Borrowings *would* be shown in an entity diagram, as the process linking books and members. Consequently, an entity diagram is most definately not the same as a data relationship diagram.

Hope this helps.

On Fri, 14 Jan 2000 08:34:14 +1030, "P Mitchell" <prmitch_at_camtech.net.au> wrote:

>Is an entity any file (table) in a database.
>So in a library BOOKS and MEMBERS are entities.
>Is there such a thing a transaction entity?
>So BORROWINGS can be called a transaction entity.
>
>So a file which resolves a many to many relationship
>such as between books and members is a transaction entity.
>
>Or are entities only sources? If so, what is the transaction file?
>
>These questions also relate to drawing diagrams.
>
>Would BORROWINGS be shown in an Entity Diagram? And is an Entity Diagram
>exactly the same as what some people call a File Relationship Diagram. For
>example, the Relationship window in Access is a file relationship diagram.
>Is it the same thing as an Entity diagram?
>
>Thanks in anticipation of any suggestions.
>
>Peter
>pmitchell_at_start.com.au
>pmitchell_at_hello.net.au
>
>
 

-- 
Mark A Preston BSc, FIAP
Business Manager, MicroFix Systems Solutions
mark_at_mpreston.demon.co.uk