A weak entity set has one or more many-one relationships to other (supporting)
entity sets
. Not every many-one relationship from a weak entity set need be supporting.
Can a weak entity participate in all relationships?
Explanation: It
cannot participate in all
the relationships. A weak entity set can only participate in relationships other than the identifying relationship.
Can a relationship have more than two entities?
There can be a simple relationship between two entities
. For example, Student attends a Class: Some relationships involve only one entity. … One entity can participate in a number of different relationships involving different entities.
Can a weak entity have a relationship that is not weak with the identifying entity?
Yes, weak entity sets can participate in
non-identifying relationships
with other entities.
Can an identifying relationship of a weak entity type be of a degree greater than two?
An identifying relationship of a weak entity type can be of a degree greater than two. An example of this would be the
ternary relationship of Supply
. Supply is a weak entity type that has three identifying relationships. These participating entity types Supplier, Part, and Project are together the owner entity types.
How do you identify a weak entity?
In entity relationship diagrams (ER diagrams), a weak entity set is indicated by
a bold (or double-lined) rectangle (the entity) connected by a bold
(or double-lined) type arrow to a bold (or double-lined) diamond (the relationship).
What kind of relationship does a weak entity have?
A weak entity type is one whose
primary key contains a relationship to another entity
. Total participation in a relationship means that every instance of an entity type must be paired across that relationship to the entity instance at the other end of the relationship.
What is the type of relationship between weak and strong entity?
The relationship between a weak entity type and strong entity type is called
an ‘identifying relationship’
and shown with a double outlined diamond instead of a single outlined diamond. The strong entity is some times called the dominant entity and the dependant entity is called a subordinate entity.
Why weak entity sets are needed?
Weak entity set is required for following reasons: 1.
To avoid the inconsistencies caused by duplicating the key of the strong entity
. … If we add primary key attributes to the weak entity set, they will be present in both the entity set and the relationship set and they have to be the same.
Can a weak entity have two strong entity?
‘Can a weak entity be related to another weak entity’ I would say No. A weak entity has no primary key of its own but does have a foreign key which is linked to the PK of another entity. Thus if you have two weak entities with the same FK id
they are infact related to the same strong entity rather than each other
.
Can a relationship be an entity?
Like entities, relationships can have attributes: we can define a sale to be a relationship between a customer entity (identified by the unique email address) and a given number of the product entity (identified by the unique product ID) that exists at a particular date and time (the timestamp).
What is the difference from relationship and weak relationship?
A strong or identifying relationship is when the primary key of the related entity contains the primary key of the “parent”. An entity is weak when two conditions are met:
The entity is existence-dependent on another entity
. The entity gets at least part of its primary key from that other entity.
How can you resolve many to many relationships between two entities?
The key to
resolve m:n relationships
is to separate the two entities and create two one-to-many (1:n) relationships between them with a third intersect entity. The intersect entity usually contains attributes from both connecting entities.
Can a weak entity have subclass?
1 Answer. IF weak entity is not in normalization then we
can not divide it in sub classes
. Because weak entity itself depends on 1 or 2 entities.so it does not contains normalize-able attributes.
Can an associative entity have a weak entity?
If an entity is placed between two entities to break up a M:N relationship, then that’s an associative entity. Since the associative entity does not have an existence of its own, it is actually
a weak entity
as well, but will always be called an associative entity.
How can we identify weak entity in ER diagram?
Weak entity is represented by
double rectangle
. The relation between one strong and one weak entity is represented by double diamond. Weak entities are represented with double rectangular box in the ER Diagram and the identifying relationships are represented with double diamond.
Which of the following set should be associated with weak entity set for weak entity to be meaningful?
2 Answers. Every weak entity must be associated with
an identifying entity
; that is, the weak entity set is said to be existence dependent on the identifying entity set. The identifying entity set is said to own the weak entity set that it identifies.It is also called as owner entity set.
What is a weak entity and what two conditions must be met before an entity can be classified as a weak entity Give an example of a weak entity?
In any case, two conditions must be met before an entity can be classified as weak:
1. The entity must be existence-dependent on its parent entity 2. The entity must inherit at least part of its primary key from its parent entity.
What is an example of a weak entity?
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.
How is a strong entity different from a weak entity?
The Key Difference between Strong and Weak Entity is that a Strong Entity has a primary key whereas a Weak Entity does not have a primary key.
Weak entity is dependent on a strong entity
whereas a Strong entity is independent not dependent on any other.
Can a weak entity be dependent on another weak entity?
Yes
. As an example, when we model “Excel”, we will find e.g. the entities “file”, “sheet” and “column” which are related as follows: file contains sheet, sheet contains column. Since each file by default contains a “Sheet1”, the entity “sheet” is dependent on “file”, i.e. a weak entity.
How can you identify the weak entity using strong entity attribute?
Strong entity is represented by a single rectangle. Weak entity is represented by
a double rectangle
.
How weak entity can be converted to a strong entity?
We can convert any weak entity set to a strong entity set
by simply adding appropriate attributes
.
What is an identifying relationship?
An identifying relationship is
a relationship between two entities in which an instance of a child entity is identified through its association with a
parent entity, which means the child entity is dependent on the parent entity for its identity and cannot exist without it.
How do you convert weak entities to relations?
While converting weak entity set into
relation schema
, the following procedure is followed; Take the Primary key of Strong entity set in which the Weak entity set depends. Then include the primary key into the relation schema of weak entity set along with other attributes of weak entity set.
Which are the two ways in which entities can participate in a relationship?
Total and partial
are the two ways that entities can participate in a relationship.
What type of relationship can’t be stored in a relational database?
Relational databases don’t allow you to implement
a direct many-to-many relationship between two tables
because it is not possible to store the data efficient.
How do you determine if a relationship is one-to-many?
A one-to-many relationship is created if only
one of the related columns is a primary key or has a unique constraint
. In the relationship window in Access, the primary key side of a one-to-many relationship is denoted by a number 1. The foreign key side of a relationship is denoted by an infinity symbol.
What is relationship entity relationship?
ERD relationship symbols
Within entity-relationship diagrams, relationships are
used to document the interaction between two entities
. Relationships are usually verbs such as assign, associate, or track and provide useful information that could not be discerned with just the entity types. Relationship Symbol.
Can a weak entity have two partial keys?
1) Weak entity is an entity which cannot exist without some other (owner) entity. 2) Weak entity does not have a primary key, but rather
a partial key
, and can be only uniquely identified by combining this partial key with a foreign key from owner entity.
What type of relationship Cannot be stored in a relational database?
There are 3 types of relationships in relational database design. They are:
One-to-One
.
One-to-Many
(or Many-to-One)
How many different type of relationships between two entity types can exist?
There are
three types
of relationships that can exist between two entities.
What is weak and strong entity sets explain with example?
The strong entity has a primary key.
Weak entities are dependent on strong entity
. Its existence is not dependent on any other entity. Strong Entity is represented by a single rectangle − Continuing our previous example, Professor is a strong entity here, and the primary key is Professor_ID.
