Quick Answer: Can Two Entities Have The Same Attribute?

What does entity mean?

1a : being, existence especially : independent, separate, or self-contained existence.

b : the existence of a thing as contrasted with its attributes.

2 : something that has separate and distinct existence and objective or conceptual reality..

How do you identify relationships and entities?

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 attributes represent in an ER model?

Attributes are the properties of entities. Attributes are represented by means of ellipses. Every ellipse represents one attribute and is directly connected to its entity (rectangle). If the attributes are composite, they are further divided in a tree like structure.

Can a relationship have an attribute?

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 difference between entity and attribute?

The basic difference between entity and attribute is that an entity is a distinguishable real-world object that exists, whereas attribute describes the elementary features of an entity. In the relational database model entities are termed as record and attributes are termed as fields.

How do you identify entities?

How to identify entity from a given problemSearch for nouns, like Teacher, Doctor, etc.Classify nouns to get a wider picture about the entities.Read the problem description repeatedly.Entities are like Persons, Students, Teachers, Courses.More items…•

How many attributes can an entity have?

In some instances, an entity will have more than one attribute that can serve as a primary key. Any key or minimum set of keys that could be a primary key is called a candidate key. Once candidate keys are identified, choose one, and only one, primary key for each entity.

What are the two ways in which entities can participate in a relationship?

which are the two ways in which entity can participate in the relationshipA. passive and active.total and partial.simplex and complex.all the above.

Can a weak entity have more than one identifying relationship?

‘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.

How do you represent a weak entity?

The foreign key is typically a primary key of an entity it is related to. 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 are the attributes?

An attribute is defined as a quality or characteristic of a person, place, or thing. … There is a difference between attributes and traits, but it is slight and some characteristics could be considered either an attribute or a trait.

What are entities attributes and relationships?

An EER database contains data about entities and their relationships. Entities and relationships are qualified by attributes representing their descriptive properties. Similar entities, that is entities of the same type, are classified in entity-sets.

What are the types of attributes?

Attributes can also be subdivided into another set of attributes. There are five such types of attributes: Simple, Composite, Single-valued, Multi-valued, and Derived attribute….Types of Attributes in ER ModelSimple attribute: … Composite attribute: … Single-valued attribute: … Multi-valued attribute: … Derived attribute:

What is strong entity type?

A strong entity is complete by itself and is not dependent on any other entity type. It possess a primary key which describes each instance in the strong entity set uniquely. … A Strong entity is represented by a square with a single line unlike a Weak Entity which contained double lines.

Can an entity be an attribute of another entity?

An entity cannot be an attribute of another entity. If you want to create a GENERALIZATION or AGGREGATION schema…it can be done… For example: … All these smaller entities will be related to the Parent entities by the Private key and Foreign key concept.

What is the relationship called when it is maintained between two entities?

What is a relationship called when it is maintained between two entities? Explanation: Binary word usually represents two attributes. … Explanation: Primary key of one relation used as an attribute in another relation is called foreign key.

Do weak entities have primary keys?

Weak entities do not have primary key attribute(s) of their own. They may have partial key. Partial Key: Portion of the key that comes from the weak entity.

How can you tell if a entity is strong or weak?

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

What are examples of entities?

Examples of an entity are a single person, single product, or single organization. Entity type. A person, organization, object type, or concept about which information is stored. Describes the type of the information that is being mastered.

Can an entity have two relationships?

There can be a number of different relationships between the same two entities. For example: Employee is assigned to a Project, … One entity can participate in a number of different relationships involving different entities.

How do attributes relate to entities?

Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes. There exists a domain or range of values that can be assigned to attributes.