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This is an old revision of this page, as edited by 161.148.140.157 (talk) at 17:48, 11 December 2007 (→‎ER diagramming tools - Linkfarm). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Common Symbols Section Needs Work

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

I have added a section entitled Alternative diagramming conventions with a diagram and explanation for Crow's Feet notation. I encourage you all to post up similar descriptions of the notations you prefer. See also Diagram is not standard section below. --Matthew 1130 13:05, 30 December 2006 (UTC)[reply]
That's not the classical Crow's Foot notation, it's IDEF1X. -- EmmetCaulfield 11:20, 6 November 2007 (UTC)[reply]

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)[reply]
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. —The preceding unsigned comment was added by 74.242.64.129 (talk) 19:54, 17 December 2006 (UTC).[reply]

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)[reply]

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


I have added a section entitled Alternative diagramming conventions with a diagram and explanation for Crow's Feet notation. I encourage you all to post up similar descriptions of the notations you prefer.

I suspect we should replace the Artist-Song relationship with a Product-Recommendation relationship, because Artist-Song is really a many-to-many relationship if we are going to be true to the real world, and we need a one-to-many relationship to best illustrate the diagramming convention. My one concern is whether the editor who originally created the Artist-Song diagram can modify it to Product-Recommendation? Matthew 1130 12:53, 19 December 2006 (UTC)[reply]

If I have the support of other Wikipedians here, I'd be happy to refactor the Common symbols section, putting the "Crow's Feet" notation at the top until such time as we have a more appropriate notation available. Please let me know. Matthew 1130 12:37, 19 December 2006 (UTC)[reply]


The problem is that there are at least half-a-dozen different diagrammatic notations, which people call "ERDs". Proponents of IDEF(1X), Crow's Foot, Chen-style, and at least two others that I can draw but can't name, will insist that their style is the "one true ERD". The Chen style (which *is* the original) is distinguished from the others by representing relationship types explicitly as "first class objects" (nodes) rather than as lines (edges). AFAICT, every diagram in any of the other (non-Chen) styles of "ERD" is isomorphic to a relational schema and, therefore, to a diagram in any of the other styles. In other words, any non-Chen "ERD" can be converted to a non-Chen "ERD" in one of the other styles by a simple relabeling and no "mapping procedure" is needed to obtain a relational schema; they are, therefore, merely alternative representations of relational schemata. There is information loss in mapping from a Chen-style ERD to a relational schema (e.g. compound attributes are flattened), so it *is* different and, IMHO, operates at a somewhat higher level of abstraction. The assertion that the Chen-style diagram "is not standard" is simply false: it may not be your favourite style (e.g. IDEF(1X)), but it is a perfectly standard Chen-style (i.e. "original") ERD and these are used for pedagogic purposes in textbooks (c.f. Elmasri & Navathe) and university courses (at least two that I know of in two different countries) all over the world. -- EmmetCaulfield 11:43, 6 November 2007 (UTC)[reply]

THE EXAMPLE DIAGRAM IS WRONG!!!!

I'm almost positive that the character should run into the creep instantiation and not the creep? Could someone verify this? Epachamo 23:02, 3 November 2006 (UTC)[reply]

What in the world is "creep instantiation"??? I've never heard of it and got no hits on Google when I searched for it. --Matthew 1130 13:08, 30 December 2006 (UTC)[reply]
The example diagram is not wrong. My group and I designed this ER diagram and I photoshopped it up. What we had in mind was that the creeps themselves would be molds for individual instantiations. For a simple example, think of Super Mario Brothers. There's a bunch of Goomba's running around, and they all look the same, but they're not the same one - they are all in different locations, and can be dealt with individually. The Goomba's in this example are Creep Instantiations, while the concept of a Goomba itself is a Creep. As to the term "creep instantiation", of course it's not real, we made it up for the project. ~ [ Matthew Tardiff 18:47, 30 December 2006 (UTC) ]
I think the issue here is that Super Mario Brothers is outside the problem domain for a number of us wikipedians here (and for a large number of visitors too). Finding a problem domain that is relatable for everyone is a high priority, do you have a preference from the ideas listed below, or perhaps another idea for a suitable problem domain:
  • Customer, Sales Rep, Sales Order, Sales Order Item, Product.
  • Borrower, Library, Section, Book, Book Category, Category, Loan, Loan Item.
  • Student, Degree, Degree Subject, Subject, Subject Instance, Course, Course Item, Lecturer, Lecturer Subject.
  • Artist, Album, Album Song, Song, Composer.
-- Matthew 1130 13:09, 31 December 2006 (UTC)[reply]
Super Mario Brothers was not the issue I was bringing up. I personally think the current diagram is a great example. Everybody can relate to games. Epachamo 18:23, 10 January 2007 (UTC)[reply]
On the contrary Epachmo, it's mostly those in your demographic and culture who relate to these games. The people who read Wikipedia are very diverse. People who are likely to read this particular article would easily include project managers, domain experts, chief financial officers, business analysts and software testers, men and women from 18 to 65 years, many of whom would be unfamiliar with computer games. I'm thinking to proceed with the Sales problem domain from the paragraph above, which I suspect is the area that people from most cultures and backgrounds would be able to relate to.
BTW, we can retain your diagram too. If you're game to reproduce the same diagram using a few different notations, it could become a very useful cross reference.
-- Matthew 1130 09:42, 11 January 2007 (UTC)[reply]
PS. Sorry, I just realised I'd taken over your section and your original question isn't answered yet.

Model -vs- Method

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)

relation vs. relationship

I was consulting this entry in order to learn about how the terms relation vs. relationship are used.

Unfortunately, after reading the entry I was even more confused, because the "Common symbols" section seems to use both words interchangeably:

"Relationships can be thought of as verbs. Examples: an owns relation between a company and a computer ..."

Is this uncertainty inherent in those words? Or is there any consensus on how to distinguish these three levels:

  • an individual tuple (a row in a table)
  • a set of tuples (a table filled with rows)
  • a type of sets of tuples (a table definition - what is actually drawn in a ER-diagram)

87.162.24.12 16:15, 21 January 2007 (UTC)[reply]

You are correct ... the Common symbols section needs a fair bit of work. I've made the correction, but it still needs more work another day.

To put it into common language, if your brother is a "relation" (aka "entity"), then you have a "relationship" with him, keeping in mind that this is a rather rough analogy.

A tuple is the correct term, and probably should be mentioned on the article somewhere, although I usually prefer the term row or record because it reaches a wider audience.

Thanks,
Matthew 1130 12:47, 22 January 2007 (UTC)[reply]

ER diagramming tools - Linkfarm

The software currently listed is mostly shareware. Can this list cleaned up?? Most of the software doesn't even draw real (E)ER! They are *DATABASE* design tools, (E)ER is a particular modeling language. --ThG 14:22, 13 January 2007 (UTC)[reply]

I agree, it would be good to separate the shareware -vs- commericial offerings in two separate subsections in ER diagramming tools. Do we have a volunteer to figure this out?
ThG, what precisely do you mean by "not even drawing real ER"? ER is not a particular modelling language, there are many different notations for ER. Was there any specific products in the list that you are concerned don't belong?
-- Matthew 1130 10:01, 14 January 2007 (UTC)[reply]
Well, ER is a particular modelling language. Anyway, I should've been more specific: ER itself sux, the real modeling language is known as EER (Extended ER or Enhanced ER), which includes leak entities, unions, derivations, etc). I'll go through the software list again and get back to you.
--ThG 19:40, 18 January 2007 (UTC)[reply]

I removed all the external links. It was becoming quite a linkfarm, violating WP:EL and WP:NOT#REPOSITORY . --Ronz 02:50, 17 February 2007 (UTC)[reply]

It's a shame because this one in particular was really good, and it's totally free and easily accessible from anywhere with an internet connection, unlike the others. You would however be technically right in that it is a relation schema designer and not an (E)ER diagram designer. --Wizgha 18:15, 18 February 2007 (UTC)[reply]
Here's the external links that were deleted from Entity-relationship model#ER diagramming tools. They look like real players in the market. Asking for volunteers to create a separate wikipedia pages for them so they can be relisted (refactored - content removed per WP:TALK):
Matthew 1130 13:52, 26 February 2007 (UTC)[reply]

The "ER diagramming tools" section is becoming a linkfarm, with the inappropriate external links. The section may be large enough to become a separate article as well. For now, I'm removing the external links per WP:NOT#REPOSITORY. --Ronz 15:49, 19 March 2007 (UTC)[reply]

Here are the (refactored per WP:TALK) latest deleted links, calling volunteers to create wikipedia pages for these products:

-- Matthew 1130 15:41, 8 August 2007 (UTC)[reply]

While creating these articles, please keep in mind WP:CORP. Thanks! --Ronz 19:29, 8 August 2007 (UTC)[reply]


I've cleaned up the links yet again, removing linkspam and entries that don't have their own articles. --Ronz (talk) 23:05, 19 November 2007 (UTC)[reply]

--Nt777 (talk) 17:06, 11 December 2007 (UTC)[reply]

I have put the folowing text in Ronz talk page:

Hello Ronz,

I undid your removal of the non-notable softwares in Entity-Relationshiup Diagram page, because it has already helped me and I belive other users in finding a solution that can be adequate for creating this diagram with an open-source solution. I was the initial person who divided the list in proprietary and open source software as I was trying to find a software that fullfill my need, and as I expected, many other people contributed with solutions and finally I dicovered Power*Architect which has recently became open-source. I am a System Analyst of a major brazilian governament company and my division has adopted this software for it´s use after these events. So I think is really helpful, and ask you to leave it. As you may already know, there isn´t any open-source solution in this area with the recent exception I told you. Our best hope is Power*Architect and brModelo. Please don´t remove this list. Other softwares may appear and this page is my (and others) first source of information.

You me reach me on nt777@hotmail.com

Nelson Teixeira —Preceding unsigned comment added by 201.70.139.207 (talk) 02:02, 6 December 2007 (UTC) 

   Please discuss this on the article talk page. There are a couple of ways where something like this could be made to work, but it's going to take more than this I'm afraid. --Ronz (talk) 02:14, 6 December 2007 (UTC)

Ok Ronz, I´m kinda new on Wikipedia editing. What would be the right way to do it ?

Nelson

Broken Links

The link to Dr. Chen's paper in the references section is broken.

Crow feet image problem

I fixed the image of the crow feet, with the vertical line and the O being the wrong way round and uploaded the new version. Bencoder 17:16, 13 May 2007 (UTC)[reply]

Beginning

The beginning of the article doesn't look encyclopedic. May I suggest: "ERM is a technique for the structure design of data on databases" or something like that? It would say the same it does now, but in a different order... Magdalena B. 12:28, 9 July 2007 (UTC)[reply]

It might also be helpful to provide a bit more context to somebody very new to the subject. For example, you might add something very basic such as, "Data models can become complicated quickly. An ERM is a tool that helps the designer to visualize and improve the design"... Bizerk44 (talk) 14:32, 23 November 2007 (UTC)[reply]

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