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14 votes
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What do the entity-relationship diagram (ERD) symbols used in DBeaver mean?

I found something while putting together this question. It seems the current standard used is IDEF1x, according to this github issue. I found a PDF cheat sheet with the following content showing all ...
Dawoodjee's user avatar
  • 498
13 votes

Visualizing Database Schema

In SSMS you can easily create diagrams showing the relationships between tables. The basic steps are: Connect to the database server Expand the Databases folder Expand the folder for the database you'...
Erik's user avatar
  • 4,771
11 votes
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Which one is an ER diagram?

One can say that a proper entity-relationship diagram is that which was created using the constructs introduced by Dr. P. P. Chen (e.g., rectangular and diamond-shaped boxes) in his famous 1976 paper ...
MDCCL's user avatar
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9 votes
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Entity-relationship diagrams and application program functionalities

You touch several subjects, therefore it is important to establish their scopes and the links that exist among them. Firstly, if the specific business domain you are working with implies (a) multiple ...
MDCCL's user avatar
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8 votes
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Can a weak entity have a primary key?

The primary key is a way to distinguish one row in a single table from all other rows in that same table. It is not a way to distinguish one row in the context of its associated rows from other tables....
Michael Green's user avatar
8 votes

How to model Parent -> Child -> Grandchild if the Child can be removed

This answer is based upon your question as it stood before the clarification about each level being a different type. Since you have identified the need for different types, I agree with my answer ...
Hannah Vernon's user avatar
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7 votes

Which one is an ER diagram?

The first one is traditional Chen's notation. The second one is modern Crow Foot or Baker's notation, used today by majority of tools and people. It is perferred because it is more readable and uses ...
Bad Pitt's user avatar
  • 274
7 votes
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How to model a Letter Transportation business context in a database diagram?

Although you stated that the structure depicted in your diagram is part of a university project, the objective should be to make it as realistic as possible, so I consider that carrying out an ...
MDCCL's user avatar
  • 8,520
7 votes

How to model Parent -> Child -> Grandchild if the Child can be removed

PostgreSQL and ltree If you're using PostgreSQL, you can check out ltree which does this and keeps things sane and indexable. CREATE EXTENSION ltree; -- required if you don't have it. CREATE TABLE ...
Evan Carroll's user avatar
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6 votes
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What is a database mission-statement?

I thought that Jeffrey Yao did a fantastic job answering this question here. I've edited it a little bit and sometimes include my own mission statement on my resume, but here's my "slightly" modified ...
Shaulinator's user avatar
  • 3,142
6 votes

Postgres 9.6 export the database structure as pdf

You need a Entity Relation Diagram (ERD) generator. The most popular and advanced one that I know of that is FOSS is SchemaCrawler. It does everything you want anyway. Though the diagrams are ...
Evan Carroll's user avatar
  • 63.2k
6 votes

Can a weak entity have a primary key?

They are both correct definitions. Orders is a strong entity. It exists on its own. OrderItems, however, would be weak. It has an order number (foreign key) and a line number (partial key). It is ...
indiri's user avatar
  • 2,211
6 votes

One and only one relationship - ER diagram to relational schema

You have several possibilities, each of them with advantages and disadvantages. Solution 1 Define a single table: AB(a b c d e f) with two candidate keys, b and e. You chose one of them as primary ...
Renzo's user avatar
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5 votes
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How do I read ERD Notation (crow's feet) to convert to Natural Language?

I'd like to answer this more definitively now using the following image (from https://www.lucidchart.com/pages/ER-diagram-symbols-and-meaning) Using the definitions of these symbols you can see that ...
raddevus's user avatar
  • 201
5 votes
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Entity set that has a relationship with itself

There's nothing in the ERD to constrain the model either way. Without suitable constraints, a child could be recorded as being born before his/her parent, a person could be their own child or parent, ...
reaanb's user avatar
  • 393
5 votes
Accepted

Settle debate between Professor and Myself on interpreting Crow's Foot Notation in an ERD

Your professor is wrong. The cardinality in almost all versions of crows foot notation is read such that the cardinality next to the entity is the cardinality of that entity. You can also see by the ...
Joel Brown's user avatar
  • 12.5k
5 votes

"Diamond Shaped Relationship" What's the formal term?

You'd have to add the crows feet (or whatever notation you prefer) for us to properly understand the diagram. I choose to interpret it as directed top-to-bottom. top table | | ^ ...
Michael Green's user avatar
4 votes
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How can I represent the entity types depicted in an ERD as relations with attribute names?

Considering the Course entity type that you describe, I have made the following assumptions: A Course is primarily identified by its CourseNumber A Course is alternately identified by its Name A ...
MDCCL's user avatar
  • 8,520
4 votes

Composite key as foreign key of multiple tables

It depends on the data model. If it is possible and correct for a row in table 1 to have a relationship with rows in tables 2 & 3 with different values of a then you must keep the two values ...
David Spillett's user avatar
4 votes

Does my entity-relationship diagram reflect the relevant business rules?

First - I agree with S4V1N completely on the Category-Business link - you need a table in between, as each business can have many categories, and each category could be tied to many businesses. ...
RDFozz's user avatar
  • 11.6k
4 votes

Entity-Relationship Diagram Software

Perhaps unsurprisingly, you're not the first person to be intrigued by the fancy, fancy pictures in that post. If you look at the comments section below, you can see user @dangerousdave asks... ...
Peter Vandivier's user avatar
4 votes
Accepted

How to generate Entity Relationship (ER) Diagram of a on-premises database using Azure Data Studio (macOS)?

Azure Data Studio doesn't have database diagramming built in. This means you're asking a shopping question, and here's how and where to ask a shopping question.
Brent Ozar's user avatar
4 votes
Accepted

Mapping a 1:1:N ternary relationship to a relational schema

A candidate key of a relation is a set of attributes such that every tuple (record) of the relation must have values differing from those of all the other tuples. A primary key can be either chosen ...
Renzo's user avatar
  • 4,080
4 votes

Alternatives to EAV model

EAV is a solution when the values to be stored cannot be identified during design-time but are captured at run-time. It sounds like your situation is slightly different - you know all the values to be ...
Michael Green's user avatar
4 votes
Accepted

If an entity's primary key must contain a foreign key, does that make the entity weak?

Strong Entities and Weak Entities are not Relational Database ideas. They are more abstract data modeling ideas than can be implemented in a Relational Database, or a Document Database, or an OO ...
David Browne - Microsoft's user avatar
3 votes
Accepted

What is the cardinality of entity relationship between Employee and Department?

What is the cardinality of (this) entity relationship between Employee and Department? Yes, this relationship ("managed-by") is an example of a one-to-one relationship. This doesn't forbid the two ...
ypercubeᵀᴹ's user avatar
3 votes

Automatically create ER diagram from database schema

It may be more trouble than its worth but there is a paper on reverse engineering relational database schemas: Clustering relations into abstract ER schemas for database reverse engineering This ...
Rankinstein's user avatar
3 votes

What does the Union sign in EER diagrams mean?

It means that the publication can be of type chapter, article, or book. That makes publication different from overlap and disjoint. When it comes to disjoint or overlap of entities, the topic ...
vidya's user avatar
  • 51
3 votes

What's the point of the relationship diamond in Entity-Relationship diagrams?

Peter Chen, who invented the ER model and the notation containing diamonds for relationships, distinguished two kinds of relations - entity relations and relationship relations. Each were intended to ...
reaanb's user avatar
  • 393
3 votes
Accepted

What's the point of the relationship diamond in Entity-Relationship diagrams?

As James K already said, there is more than one set of rules for forming ERDs, and more than one answer to your question. But, to deal with your question from a generic point of view, here goes. ...
Walter Mitty's user avatar
  • 4,316

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