Re: E/R modeling: relationship's attributes

Sticky Bit wrote:
> Hello,
> In Chen's Entity/relationship model, relationships too can have attributes.
>
> How should I represent these relationships in a database? In my view, if I
> represent these relationships' attributes as fields in a table, the
> relationship becomes a relation: an entity...
>
> Thanks for your insights

 From the cdt glossary:

> [Entity]
> Thing of interest. (ISO)
>
> "An entity is a 'thing' which can be distinctly identified. A specific
> person, company, or event is an example of an entity. "
> ("The Entity-Relationship Model-Toward a Unified View of Data", 1976, P.
> Chen., http://www2.cis.gsu.edu/dmcdonald/cis8140/Chen.pdf )
>
> Edward Yourdon, who describes E/R in his work Modern Structured
> Analysis, (Prentice Hall 1989) defines the concept of Entity
> as having three properties:
>
> 1. Each representation of an entity can uniquely be identified
> 2. Each representation of an entity is playing an important role in
> the system it lives in. (it has to have a reason to be there)
> 3. Each representation of an entity can be described by one or more
> attributes (data-elements, like name, age, quantity)
>
> This term is often used when doing conceptual data modeling.
> When it is used with a particular product, technique, or technology,
> such as XML, refer to the use of the term within that "namespace" using
> an adjective, such as "XML entity" to distinquish it from the more
> generic use of the term.
>
> For subtleties (e.g. strong and weak entity) -
> please search the web.

and:

> [Table/Row/Column] (SQL-DBMS)
> Table: A collection of columns (the table header) and rows (the body).
> Row: A collection of values, conforming to the table header columns.
>
> One table may contain data about one entity,
> about several entities, about one or several
> relationships or any combination.
> A column can be seen as the attribute of the
> entity/one of the entities/relationships
> about which the table is concerned.

HTH, ... if it didn't you might try to provide a more helpfull text. I'll repost the whole glossary next. Received on Mon May 01 2006 - 20:54:12 CEST