- What is the difference between a composite attribute and a multi valued attribute?
- What is weak entity explain with example?
- What does ERD stand for?
- How foreign key is represent in ER diagram?
- What is a relationship called when it is maintained between two entities?
- How do you determine a relationship in ERD?
- What is a weak entity type?
- What is a weak relationship in database?
- What is a strong or identifying relationship and how is it depicted in a crow’s foot ERD?
- Can a weak entity have two owners?
- Can a weak entity have a primary key?
- What is a strong relationship in database?
- What cardinality means?
- What is an identifying relationship?
- Does a weak entity have a strong or weak relationship?
- How can I make my weak entity strong?
- What two conditions must valid entities meet?
- How do you identify entities?
What is the difference between a composite attribute and a multi valued attribute?
Most attributes are atomic attributes.
Multivalued A multivalued attribute may have one or more values for a particular entity.
Composite Composite attributes are not atomic because they are assembled using some other atomic attributes..
What is weak entity explain with example?
A weak entity is an entity that cannot exist in a database unless another type of entity also exists in that database. Weak entities cannot exist without the identifying relationship. Weak entities do not have primary key attribute(s) of their own. They may have partial key.
What does ERD stand for?
ERDAcronymDefinitionERDElectronic Report DistributionERDEmergency Recovery DiskERDEclipse Resource DatabaseERDEvent-Related Desynchronization56 more rows
How foreign key is represent in ER diagram?
The ER model does not use foreign keys to represent relationships. It uses lines between boxes. The lines have some kind of indicator for cardinality at either end or both ends. Sometimes, a relationship will be indicated separately by a diamond.
What is a relationship called when it is maintained between two entities?
Explanation: Ellipse represents attributes, rectangle represents entity. 6. What is a relationship called when it is maintained between two entities? … Explanation: Primary key of one relation used as an attribute in another relation is called foreign key.
How do you determine a relationship in ERD?
A SIMPLE EXAMPLE. A company has several departments. … Identify Entities. The entities in this system are Department, Employee, Supervisor and Project. … Find Relationships. We construct the following Entity Relationship Matrix:Draw Rough ERD. … Fill in Cardinality. … Define Primary Keys. … Draw Key-Based ERD. … Identify Attributes.More items…
What is a weak entity type?
In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key. The foreign key is typically a primary key of an entity it is related to.
What is a weak relationship in database?
A weak, or non-identifying, relationship exists if the primary key of the related entity does not contain a primary key component of the parent entity. Company database examples include: Customer(CustID, CustName)
What is a strong or identifying relationship and how is it depicted in a crow’s foot ERD?
What is a strong (or identifying) relationship, and how is it depicted in a Crow’s Foot ERD? A strong relationship exists when en entity is existence-dependent on another entity and inherits at least part of its primary key from that entity. The Visio Professional software shows the strong relationship as a solid line.
Can a weak entity have two owners?
‘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 weak entity have a primary key?
As the weak entities do not have any primary key, they cannot be identified on their own, so they depend on some other entity (known as owner entity). The weak entities have total participation constraint (existence dependency) in its identifying relationship with owner identity.
What is a strong relationship in database?
A strong or identifying relationship is when the primary key of the related entity contains the primary key of the “parent”.
What cardinality means?
Cardinality means two things in databases. … When applied to databases, the meaning is a bit different: it’s the number of distinct values in a table column, relative to the number of rows in the table. Repeated values in the column don’t count. We usually don’t talk about cardinality as a number, though.
What is an identifying relationship?
In database terms, relationships between two entities may be classified as being either identifying or non-identifying. Identifying relationships exist when the primary key of the parent entity is included in the primary key of the child entity.
Does a weak entity have a strong or weak relationship?
It instead has a partial discriminator key. A weak entity is represented by a double rectangle. The relation between one strong and one weak entity is represented by a double diamond….Difference between Strong and Weak Entity:S.NOStrong EntityWeak Entity1.Strong entity always has primary key.While weak entity has partial discriminator key.4 more rows•Apr 22, 2020
How can I make my weak entity strong?
Though weak entity set can be converted into strong entity set by simply adding appropriate attributes, this approach results in the redundant storage of primary key. ii. The primary key of a weak entity set can be inferred from its relationship with the strong entity set.
What two conditions must valid entities meet?
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.
How do you identify entities?
Name each entity using a noun in the singular form (e.g., Employee not Employees). Use a word that is precise and clearly identifies the object. When appropriate and needed to distinguish similar entities, use an adjective to further describe the noun (e.g., Permanent Employee, Temporary Employee).