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May 21, 2013 · 4. In an ER diagram, I believe when the relationship is strong, i.e., the primary_key of the parent forms a composite or non-composite primary_key in the child entities, we use a solid line to depict that. Similarly, for the case when the relationship is weak, which means the primary_key of the parent is not used as a primary_key in the child ...
Feb 7, 2011 · An entity is a term from the entity-relationship model. A relational model (your database schema) is one of the ways to implement the ER model. Relational tables represent relations between simple types like integers and strings, which, in their turn, can represent everything: entities, attributes, relationships.
48. Associative entities are used when you need a relationship to be involved in a relationship. For example: For a normal many-to-many relationship between Student and Course, we would use just a diamond. However, if we want to associate Enrollment with Teacher, we can turn Enrollment into an associative entity.
Jan 29, 2020 · And table is used to express it, but there is a slight difference. Table expresses not only entities, but also relations. For example, assume that you want to make a database of projects and employees of a company. Entity is a unit of information that has meanings by itself. In this case, there will be two entities - "Project" and "Employee".
Jan 20, 2011 · A weak entity is one that can only exist when owned by another one. For example: a ROOM can only exist in a BUILDING. On the other hand, a TIRE might be considered as a strong entity because it also can exist without being attached to a CAR. edited Jun 18, 2018 at 7:23. Heniam.
Feb 16, 2019 · Entity Type: It is collection of entity having common attribute. Entity Instance: An entity instance is a single occurrence of an entity. So to clarify your confusion, entity is a more abstract or general way of referring to an entity instance or a type.And yes EMPLOYEE is an entity type. References: instance, entity, another answer with example.
Apr 17, 2015 · 3. As you know Weak Entity is table which does not have a primary key but the primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator. The relationship between weak entity and strong entity set is called as Identifying ...
Oct 24, 2011 · Parent - The entity on the "one" (/1) side of a relation with another table. Child - The entity on the "many" (/N/*) side of a relation with another table. Parent <-- Child. The child points to the parent. So each child knows who its parent is. And each child has exactly one parent.
Jun 26, 2016 · Consider a marriage - a relationship with two mandatory roles filled by the same entity set. In most relationships, the entity sets also define the roles, but when an entity set appears multiple times in a single relationship, we distinguish them in different roles. In the example above, a Patient can Purchase Medicine with or without a ...
Jul 9, 2016 · 1. What i know about weak entity is that they cannot exist without strong entity:-. i.e there must be a strong entity from which key (foreign key) has to be taken by weak entity. example : a HOTEL (strong entity) and ROOM (weak entity), HOTEL is strong entity because they can have their existence by their own (independently) while ROOM is weak ...
