Talk:Entity–relationship model

I doubt that an Entity-relationship model can be called a data model. It is a method to design data models. --Udo Altmann 13:42, 18 Oct 2004 (UTC)

If it were a method it would be called the Entity-Relationshp Method. The researchers at the ER 2004 would be highly amazed by your claim that the ER model is not a data model. -- Jan Hidders 11:05, 19 Oct 2004 (UTC)

Sorry for again starting a method discussion. The introduction sounds as if the ERModel is a data model for a data model - a meta model - which for me has an implicit methodological aspect. I think this was, what caused my discomfort. Wouldn't it be simplier (and still correct) to say "A Entity-Relationship model is a high-level description of a conceptual data model. Entity-Relationship models include graphical notations for representing such data models in the form of entity-relationship diagrams". --Udo Altmann 09:24, 1 Nov 2004 (UTC)

It would be incomplete. As already explained, the ER model is a meta model (with a graphical notation and some semantics), so that is of course what the introduction should explain. Why are you uncomfortable with that? I also fail to see why you connect that with a methodological aspect because that link is very very weak. There is no fixed method to arrive at your model and there is no fixed method to go from your ER diagram to your relational model, and, as was already explained, the scope of the ER model is much wider than just a method to arrive at your relational model. So what then is it exactly that you mean with this mysterious "methodological aspect"? It's still as if you want to believe that the ER model is a method. Please don't. Apart from being incorrect that view is much too narrow and does unjustice to the ER model. :-) -- Jan Hidders 13:53, 2 Nov 2004 (UTC)

I must say that I agree at least on the lack of clarity of the first sentence. Either its meaning is wrong or it is poorly written. Whichever it is, the first sentence of the introduction is misleading to the least. 194.221.74.7 08:54, 8 June 2006 (UTC)

I agree - calling an entity a 'discrete object is not very accurate, but then again, what would be a more accurate term? Rp 10:20, 10 July 2006 (UTC)

I'm not sure about a relationship having an attribute. How can this convert into a logical model?--Nick 18:11, 4 March 2006 (UTC)

You have a good point there - I think conversion from ER model to logical relational model must be treated if only to make the point that the ER model is not an informal drawing technique but has a sound formal basis. Rp 10:20, 10 July 2006 (UTC)

Another issue is the (universal) confusion between entities and entity sets, relationships and relationship sets. This article dutifully explains the "correct" use of the terms, but before it does so has already used them "incorrectly" (i.e. how everybody uses them in practice) quite a few times. So either the terms e. set and r. set should be omitted or a more thorough clarification is in order. Rp 12:17, 10 July 2006 (UTC)

Symbols

Any chance someone could mock up a set of images showing what these symbols are supposed to look like? Describing them is all well and good, but a picture can be worth a thousand words.  :) Thanks, Eirikr 03:45, 8 Apr 2005 (UTC)

I've added a first example diagram. I'd like to include some more images but I'm having trouble deciding which examples would best clarify some of the text. Also, I'm wondering if it'd make any sense to upload the original Dia files and refer to them from the Image:erd-*.png nodes for if anyone else wants to change something in the coloring or whatnot... --BigSmoke 16:27, 12 Jun 2005 (UTC)

Agreed. Just for fun: Can we get an ERD of the wiki that wikipedia et al. use?

Diagrams and ER 2004

As far as I know there are multiple ways of drawing ER diagrams. I use arrows. Yet the article implies that there's only this one way.

Where's the explanation/links about ER 2004? --Khokkanen 12:53, 10 June 2006 (UTC)

Diagram is not standard

This diagram is not remotely similar to the methods used by nearly all of the major ER tools in use today. IDEF1X is far and away a more common mechanism, as are derivatives of that method that vary primarily in the symbols used to indicate n-ary relationships.

I suggest we replace this article with one that is similar to the article referenced by the IDEF1X link (US Navy, I think). This article is absolutely useless for practitioners and students of ER models. User:nickmalik 11:47 15 Oct 2006 {PDT)

I strongly disagree. Since the article's subject is the Entity-Relationship Model it should use the classical notation. Any other choice would be somewhat arbitrary as there are many tools and many dialects and none of them is really predominant. Most (database) textbooks I know use the classical notation. -- Jan Hidders 21:39, 15 October 2006 (UTC)

I suppose we should use Roman Numerals for math articles since they are a more "classical representation". I have been involved with data modeling for nearly 20 years and have never seen an ER diagram like that. I agree that IDEF1X is generally considered the best representation.

What about the cardinalities of relationships? I thought these were annotated by numbers on the arcs of the relationships?Jam2001 12:50, 18 October 2006 (UTC)

Yes, that is correct. Why? -- Jan Hidders 21:29, 18 October 2006 (UTC)

Example Diagram

As a side note, shouldn't the character run into the creep instantiation and not the creep? Epachamo 23:02, 3 November 2006 (UTC)

what up game ?