Questions tagged [entity-relationship]

An entity-relationship model (ERM) is an abstract and conceptual representation of data, information aspects of a business domain or its process requirements. Ultimately ERM is being implemented in a database.

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Modelling a daily event with Entity-relationship diagram

I am new to ERD and I have been tasked with creating a ERD of a store chain. The chain contains several stores which all have several items being sold in them. After every day every store is supposed ...
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How to create an ER Diagram for this scenario?

You are asked to design the ER diagram for a database to manage data for athletes competing at the O athletic game. Requirements are as follows: ● Each participating team has a name and a manager. ●...
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Relationship attributes having relations with another entity

I am creating an ER Diagram for an assignment using UML and cannot find much information on using relationship attributes. Can relationship attributes have relations with another entity? I have drawn ...
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How to pass a data from formType parent to formType child

I have a form that takes place in several stages, including : Step 1 : a simple form, based on an entity 1, which records a first part of the dataset. Step 2 : a parent form (based on entity 1 in ...
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Normalized ER Diagram - Delivery System

I need to create a normalized ER diagram, but I'm having so many problems to understand normalization. The company Food and Cia delivers meals in the delivery system and wants an information ...
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ER - normalization

I need to create an ER diagram, but I'm not sure if it is correct: Consider the following description of a requirement and develop a standardized ER diagram: A pharmacy wants to record your sales ...
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Can i have 2 ER diagrams for one database

The database I have set up is accessed by normal users and an admin with both user types having different permissions. Should I have 2 ER diagrams? The relationships I've worked out are as follows: ...
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How to implement chosen answer in a Q&A app like stackoverflow

I want to design a database for Q&A app like stack overflow. I have two tables: Question and Answer. each Question can have many Answer but each Answer has only one Question. Now, i want user ...
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Different relationship between 2 entities

In my project I have a part where says - An airline has many flights and each flight has one source (airport) and one or more destinations (airports). For each source destination pairs, you have ...
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How to manage relationships between “subsets” of entity sets

I have, in total, 5 sets of entities. Lets call them entity sets A, B, C, D and E. For this specific problem, lets assume all entity sets are strong and the attributes of each are not important. In ...
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Toad Notation - What do (Ix#)'s mean?

So, I'm trying to visualize a database, and I have some tables put together which consist of a mix of object-oriented and relational; just trying to tie them together. My issue is, I can't seem to ...
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Does MySQL Workbench Diagram Maker allow for relation tables?

I'm making an ER diagram in MySql Workbench, but I don't see an easy way to connect tables satisfactorily. What I want is something like this: which I am able to do for single relationships with a "...
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ER Model to R Model - can the internal attributes of a relationship be the primary key?

as I quote in the title, "Can the internal attributes of a relationship be the primary key?". That is, supposing you have: E1 (A, B, C) E2 (D, E, F) R (G, A, B, C, D, E, F) Supposing to have a "...
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How Laravel defines name of the foreign-key as default in Model file?

I am new at Laravel and I am wondering how actually Laravel determines default foreign key name. According to the Laravel document, it says "Eloquent determines the default foreign key name by ...
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weak entity depending on either one of two other entity

Consider that we have employee as an entity and it's family member as a weak entity. We want to have family members health record. so we add another weak entity "Health Record". The ER diagram would ...
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A 1:1 relationship with auto update/insert semantics (Fluent API)

I have plenty of ways to implement around this, but I'm curious about whether or not one specific implementation is possible in EF6 using the Fluent API. Take the following two classes as a starting ...
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Modelling multiple many-to-many relationships in Dynamodb

I am trying to model the following relationship in a single Dynamodb table. User -> many to many -> Game User -> many to many -> Group In words: A user can have many games, and multiple users can ...
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Filter in ERD-Diagram

could someone help me with this problem. I have some "filter-options", its RANGE and CODE. With these filters i have to inner-join the BOOST-Entity on RANGE and CODE to get RESULT1. Now i have to ...
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Modelling Relational Data in Firestore with Angular

I am aware that there are plenty of questions asked to this topic, but the other questions do not seem to answer my rather case-specific one. I have the following Structure: Each User via FireAuth ...
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Many-to-many relationships with EF Code First and multiple schemas

I am trying to create a db structure using multiple schemas. I am now at the point where I need to link my User table (authentication schema) to my TrafficArea table (assets schema). However when ...
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How to properly model Recursive category in er model?

I would like to know, how to properly show recursive categories in er model? I have table Employee with details such as Name, Age, Email etc. and I have self-reference with EmployeID which means ...
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Represent a route in er diagram that is dynamic

I have to implement a faculty system where if a faculty wants to apply for a leave, his leave application follows the path Faculty -> HOD -> Dean -> Director So, I have to store this route in an ER ...
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computerised cab service management system

Cab service company employees are categorized into sections. Each section has a section manager. Section No and a fixed basic salary rate is assigned to a section. They keep data on Emp-no, NIC No, ...
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How to write nullable properties for EF6 table definition class with C#?

I want to write an C# class to describe a database table with an relation to itself, later to be used with Entity Framework 6. I have the following C# code to implement the above shown table: public ...
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Should I model the database admins in my ERD/relational diagram?

I'm trying to model a database (for my assignment) that involves two user groups that post content to the platform. A third user group would be the system/database admins that are responsible for ...
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Entity or relationship

I am drawing an ER diagram. Movies (title, year, and rating) are shown in theaters (name and city). A movie can be shown in many theaters and a theater can show many movies. "Show" should hold ...
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I need to relate a table that is created from a relationship with another table that is created with another relationship

the teacher of a subject in a classroom, which is in the relationship N: N: N, makes many assessments of many students. I do not know how to create the table to let me do this.
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How to structure Firestore data to support large a many to many relationship?

My UI needs to support the following functionality: Users can follow other users A user can like a post A user needs to see on ONE page all posts that any of the users they follow (and/or themselves) ...
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Is this potential loop a problem in my database ERD?

I am creating an ERD for what will eventually be a fairly simple (I think) CRM database. I know enough about database design that I am aware loops can be problematic. However, I don't know enough to ...
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Relationship Model between Three Tables in a Fourth Table

So I have two tables -- Student table and Staff table, I also have an Item table, the plan is for students or staff to take custody of an item, put in another way, for an Item to have a custodian (...
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Unique attributes within a record in an ER Diagram

Is there a way to show uniqueness of attributes in an instance of a relation within an ER Model. For example : For a sports team playing in games. One team cannot play itself. The ‘Home’ and ‘Away’ ...
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How to create model without using Entity Framework in C#?

I need to know how to implement the relationship in the model without using Entity Framework in C#. Please give me a solution using this ER diagram. class Student { public int ...
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What is the correct way to represent this ER diagram?

I'm trying to do a ER diagram of this database problem. "Products have a unique 13 digits code and a description, they also can be organized by category that have a name and a number. There can be a ...
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How to properly manage associated JPA entities with OneToOne BiDirectional relation?

Let's say 2 entities are given: master and dependant. They are defined in DB usually like dependants.master_id -> masters.id, i.e. the dependant entity holds the reference to the main entity. In ...
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er diagram, one to many/many to many

I try to make a er diagram, and my professor told me that the the er diagram still only support one product per order, how can i make the order support multiple products? the image link is in the ...
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Online food ordering er-diagram

Is their any Normalization problem for this er-diagram? And how to add a table for collection type( delivery or self pick up)?
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Modelling a series of elements of the same entity in JPA (one-to-one relation)

I created an entity/table for a book, and I want to achieve that each element can reference another book to create a series. I came up with this: @Entity public class Book { @Id @...
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Is this relationship OneToMany or ManyToMany?

I have two tables ARTICLE and FAQ ( frequently asked questions ). I'm trying to establish a relationship between these two tables but I'm confused! What I want to achieve is that article can have ...
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C# EF-relationship 0..1-1 between two entities when the dependent one has only foreign key and no primary key

How to set EF-relationship between two entities where the first(main) entity has a primary key, but the second(dependent) one has no PK, only foreign key - on the first entity. public class Dogovor { ...
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save entity array under another entity CoreDataRelationships

Im working on an app where a merchant can add a bunch of products into a persons tab. After selecting the customer from a table view the user can see a list of products and the total amount which I'd ...
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1answer
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Weak entity with 2 different owner entities

Weak entity with 2 owner entities I have a database I am trying to design with 3 entities: Store, Item, and Wishlist. Stores and Wishlists exist on their own, and are therefore strong. Items, however,...
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1answer
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Entity Framework - Invalid Column Name 'User_ID"

I have a project written with C# on the top of ASP.NET MVC 5 framework. I am using Entity Framework 6.2 ORM to interact with my database. I have the following 2 entity classes public class User { ...
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inserting some values in one field

How can I insert many values into one database field? Is it possible? I want to make a table for meetings, and invite many persons. So how can I add persons to my meeting table?
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RealmSwift : All the realm rows are displayed twice

I am learning to develop on Swift, so sorry if my questions seem stupid :D On my app, I need 3 objects : Car, Station & Conso A Car Object can have many Conso A Station Object car have many Conso ...
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Converting ER diagram into relational schema

I have the following diagram and I have converted it into a relational schema, but can someone please confirm whether it is right. SportsPlayer (PlayerID, Name, Height, Weight, Age, Gender) ...
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1answer
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Plymorphic Many to Many relationships in EF

I have a polymorphic collection on one entity type that contains a collection of objects that are the child types of it. the child types are all stored in different tables in the db. I need to map ...
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1answer
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How does cardinality work in an ER diagram when considering the dimension of time?

I will going to explain my question using the fragment of a problem in which there are two entities: 🔸 Airplane 🔸 Location And a relationship to link these entities: 🔸 Send Logic 1: An ...
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Building a relationship between 3 tables

I am in the process of designing a part of a Database for a pet project of mine, and I am in this predicament. I have 3 tables: PET, BOOKING, SERVICE. PET (attributes):- Pet_Id => Primary Key,...
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Can there be a relationship between 2 subclasses?

Let's say I've got a superclass E and 2 subclasses E1 and E2. Can there be any relationship between E1 and E2 without any previous knowledge?
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Complex and multiple connected database relations in MongoDB

I am currently trying to model a MongoDB database structure where the entities are very complex in relation to each other. In my current collections, MongoDB queries are difficult or impossible to ...

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