Chen Notation for ER-diagrams

[HeroGamers]

I looked around for quite a while, and tried to see if anyone had made it possible to use the Chen notation in PlantUML yet, and I could only find the old Issue for the Crow's Foot notation (#39), yet no apparent implementation for the Chen notation, which is what I'm being taught in university, and which seems to be used widely (though it might be an older notation..?)

I'd definitely appreciate having the notation added to PlantUML, and I bet it would be great for others as well!

Some references: https://vertabelo.com/blog/chen-erd-notation/ https://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model#/media/File:ERD_Representation.svg Chapter 6 of Database System Concepts (https://www.db-book.com/)

[ahorn42]

I really like this this idea!

There was already a suggestion here: https://github.com/plantuml/plantuml/issues/39#issuecomment-474405783

[PaienNate]

Really like this idea too.

[Benjamin-Davies]

I've started work on an implementation for this. It's mostly done, I just need to change the shape of the relationships and tweak how the layout is done. https://github.com/Benjamin-Davies/plantuml/tree/cheneer

It would be good to get some feedback on the syntax.

@startchen movies

entity DIRECTOR {
  key attribute Number
  attr Name {
    Fname
    attribute Lname
  }
  attribute Born
  attribute Died
  attribute Age
}

entity CUSTOMER {
  key attribute Number
  derived attribute Bonus
  multi attribute Name
}

entity DVD {
  key attribute Code
}

relationship RENTED_TO {
  -1 CUSTOMER
  -N DVD

  -(N,M) DIRECTOR

  attribute Date
}

@endchen

[The-Lum]

@Benjamin-Davies:

Here are some first questions, for the syntax point of view:

• Just for my comprehension, what is the meaning of the first E, on Chen EER?
• Could you plan to manage long name and alias ?
  • entity "Nice Director" as DIRECTOR {...
• Could you plan to manage stereotype for styling ?
  • entity DIRECTOR <<pink>> {...

Regards, Th.

[HeroGamers]

@Benjamin-Davies

Looks nice - I do have some feedback/questions for the syntax:

• Would it be possible to write relationships like:

  CUSTOMER -1- RENTED_TO
  RENTED_TO -N- DVD
  RENTED_TO -(N,M)- DIRECTOR

• I saw that you wrote key to some of the attributes, but wouldn't it be an idea to keep it similar to how the current Crow's Notation is made in PlantUML, such that the biggest difference actually is the layout, structure and shapes, but otherwise keeps the same way of writing it
• Would this also support adding types, ie. attribute Born : TIMESTAMP?

But otherwise great work!

Best regards, Marcus

[Benjamin-Davies]

• Just for my comprehension, what is the meaning of the first E, on Chen EER?

The first E in EER stands for enhanced or extended (see Wikipedia). All ER diagrams are also EER diagrams, but EER adds support for subclassing of entities.

All of your suggestions look good. I'll probably end up dropping the "attribute" keyword and moving "key" etc. to be stereotypes, for consistency with other PlantUML diagram types.

[hinogi]

So what is the actual syntax now?

[hinogi]

@startchen movies
<style>
.red {
  BackGroundColor Red
  FontColor White
}
.blue {
  BackGroundColor Blue
  FontColor White
}
</style>

entity "Director" as DIRECTOR {
  "No." as Number <<key>>
  Name {
    Fname
    Lname
  }
  Born : DATE
  Died<<red>>
  Age<<blue>>
}

entity "Customer" as CUSTOMER {
  Number <<key>>
  Bonus <<derived>>
  Name <<multi>>
}

entity "Movie" as MOVIE {
  Code
}

relationship "was-rented-to" as RENTED_TO {
  Date
}

RENTED_TO -1- CUSTOMER
RENTED_TO -N- MOVIE
RENTED_TO -(N,M)- DIRECTOR

entity "Parent" as PARENT {
}

entity "Member" as MEMBER {
}

CUSTOMER ->- PARENT
MEMBER -<- CUSTOMER

entity "Kid" as CHILD <<weak>> {
  Name <<key>>
}

relationship "is-parent-of" as PARENT_OF <<identifying>> {
}

PARENT_OF -1- PARENT
PARENT_OF =N= CHILD

entity "Little Kid" as TODDLER {
  FavoriteToy
}

entity "Primary-Aged Kid" as PRIMARY_AGE {
  FavoriteColor
}

entity "Teenager" as TEEN {
  Hobby
}

CHILD =>= d { TODDLER, PRIMARY_AGE, TEEN }

entity "Human" as PERSON {
}

PERSON ->- U { CUSTOMER, DIRECTOR }
@endchen

ok found it in the implementation added some spacing and color examples

[The-Lum]

Hi all,

Here is the corresponding image:

Doc. can be improve here:

• http://alphadoc.plantuml.com/doc/markdown/en/er-diagram

Thanks for your contributing... Regards, Th.

[VladimirAlexiev]

@The-Lum I fixed links between ER and IE, and added a last section "Complex Example" with the above example