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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.

Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, or ERDs.

The main components of the ER diagrams are the entities and the relationships that exist among them. For example with the original notation, in the relational databases tables are shown as boxes, its attributes as ovals and their relations with other tables with lines.

The three schema approach to software engineering uses three levels of ER models that may be developed:

  • Conceptual data model is the highest ER model, that contain least granular detail but establishes the overall scope of what to be included in the model set.

  • Logical data model contains more detail than the conceptual ER model. Operational and transcational data entities are defined.

  • Physical data model - one or more such models can be developed from each logical ER model. Normally developed to be instantiated as a database, therefore each physical model must contain enough detail to produce a database.

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How do we use Integer or Long type of objects as Foreign key mapping in JPA/Hibernate?

I tried below sample code which does not seem to work, while trying to fetch the object from table, hibernate tries to set the User Object on top of Long objects and fails when tried to load the Parent entity which has this createdBy field any…
Hashir Labs
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Android Room: One to Many Relationship Database following MVVM architecture

Cannot find enough resources to create a one-to-many relationship following MVVM architecture. So far this was the close a topic: Android Room: How works One to many relationship + examples Have read: Android Room One-to-Many Relationship Related…
Gilbert Almazan
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How do we use Routine Group in MySQL workbench?

Since I can't find a way to add a routine to a diagram, I don't know how to use Routine Group tool.
JatSing
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Better way to design Attendance Managment Design

Good evenings. I trying to make simple Attendance Managment Sytem using MySQL. My goal is teacher can mark student attendance in given day and student can see his/her attendance. But i am having problem about design. First, let me explian my…
xKralTr
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Can strong entity have foreign keys?

I want to identify this ER diagram's strong and weak entities. I doubt that can a strong entity have foreign keys. What are the strong entities and weak entities of this ER diagram?
Kushani5j
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How to implement rental limit for different members in DVD rental database

I am designing a DVD rental database. There are two types of Users, Members and Staff, who all have a membership card. The MEMBERSHIP_CARD could be my supertype and MEMBERS and STAFF would be my subtypes. I am trying to implement a limit for renting…
Alfonso
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Find the customer_IDs of the customers who

My code is: CREATE TABLE `table_a` ( `id` INT NOT NULL AUTO_INCREMENT, `value` varchar(255), PRIMARY KEY (`id`) ) ENGINE=InnoDB; CREATE TABLE `table_b` LIKE `table_a`; INSERT INTO table_a VALUES (1, 'A'), (2, 'B'), (3, 'B'); INSERT INTO…
user20305065
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One to Many JPA relationship with 3 entities produces error IllegalArgumentException Entity must not be null

I am trying to create a schema where I have 3 tables, Customer, Orders, and Products that have One to Many relationships. For example, 1 Customer can have many Orders and 1 Order can have many Products (is this possible?). I am able to add a…
Hendrix
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ER Diagram and recursive relation

I have a quick question about ER diagram. My question is would a sender and receiver be a recursive relation? Like if I want to send money to someone in a transaction via PayPal.
Pratik patel
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Database One to Many relationship, with child entity identifiers always starting from zero

I want to be able to have a relationship between a parent "article" entity, and many child "image" entities, but have the identity of the child start at zero in relation to each parent. I'd imagine that involves 2 primary keys defined in the child…
Gers
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Is it possible to make ER (entity-relation) diagram of Non SQL Databases like firebase?

I am working on my university project and I am using Firebase as a database for which I have to make UML diagram. I had mostly seen the example for ER(entity-relation) Diagram in SQL databases. I also heard that ER Diagram is created only for SQL…
Badar
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ER arrows with cross specification in ER diagram

A normal entity diagram usually use circles or a straight line to denote a zero or one to many relationship, respectively as in the following image: However, recently I've seen something new, as in the following image, and was wondering what the…
moth
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What is the difference between participation constraint and referential integrity constraint?

Apologies in advance if this is a silly question. I recently faced this question while revising for databases, so I wish to check if my understanding is correct. I understand that participation constraint is referring to the number of instances of…
IcyBloom
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Relationships between 3 Entities in a ternary relationship

we are tasked with creating a database which has three entities team, user, course. A course will have multiple students and multiple teams in it. A student and professor can belong to many courses. However, a user with the type of student can only…
this_geek1991
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How can I automatically generate an ER diagram to visualize table relationships of an ORM in SQLAlchemy?

I am trying to find a way to generate an entity relationship diagram based on an ORM which has been created using SQLAlchemy. The ORM might look like this and contain multiple tables, that are related via Primary and Foreign Keys: from sqlalchemy…
omoshiro
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