What is an ER diagram give an example?
What is an ER diagram give an example?
1. Entity. An entity is an object or component of data. An entity is represented as rectangle in an ER diagram. For example: In the following ER diagram we have two entities Student and College and these two entities have many to one relationship as many students study in a single college.
What are the major components of ER diagram explain with examples?
What are the components of an entity-relationship diagram? ER diagrams or ERD’s are composed of three main elements: entities, attributes, and relationships. Entities – typically displayed in a rectangle, entities can be represented by objects, persons, concepts, or events that contain data.
Is an example of composite attribute?
A typical example of a composite attribute is a person’s address, which is composed of atomic attributes, such as City, Zip, and Street.
What is relational model with example?
The relational model in DBMS is an abstract model used to organize and manage the data stored in a database. It stores data in two-dimensional inter-related tables, also known as relations in which each row represents an entity and each column represents the properties of the entity.
Which of the following is represented by an ER diagram?
Which of the following symbols represent entity sets in an ER diagram? Explanation: Rectangles divided into two parts represent entity sets in an ER diagram. The upper rectangle contains the name of the entity sets. And the lower rectangle contains the attributes.
What are the three main components of ER?
The three main components of the ER Model are entities, attributes and relationships. In ERM terms, an entity is a “thing” within the organisation, that we want to keep information about, such as a customer, employee or course.
Is phone number a multivalued attribute?
The existence of more than one phone number turns the phone number attribute into a multivalued attribute. Because an entity in a relational database cannot have multivalued attributes, you must handle those attributes by creating an entity to hold them.
What is relational model and explain relation schema and instance with an example?
Relational schema: A relational schema contains the name of the relation and name of all columns or attributes. Relational key: In the relational key, each row has one or more attributes. It can identify the row in the relation uniquely. Example: STUDENT Relation.
What is the use of ER model?
Database design: ER diagrams are used to model and design relational databases, in terms of logic and business rules (in a logical data model) and in terms of the specific technology to be implemented (in a physical data model.)
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. I don’t understand why this is accepted, it’s simply wrong.
What is entity and entity set?
An entity in DBMS is used to represent any real-world object, while an entity set in DBMS is a set or collection of entities of similar types. In relational models, i.e., the tabular representation to represent data, each row in a table is a separate entity while the whole table is an entity set.
What is entity type and entity set?
Entity Type : Each entity belongs to the student type. Hence, the type of entity here is a student. Entity Set : The complete data set of all entities is called entity set. For the above table, the records with student id 1, 2, 3, 4 are the entity set.
What are the features of ER model?
The extended E-R features are specialization, generalization, higher- and lower-level entity sets, attribute inheritance, and aggregation. Specialization – An entity set broken down sub-entities that are distinct in some way from other entities in the set.
What is attribute explain with example different types of attribute?
Attributes are properties which describes each member of an entity set. For example, an EMPLOYEE entity may be described by the employee’s name, age, address, salary, and job. A particular entity will have a value for each of its attributes and hence forms major part of data stored in database.
Is date of birth a multivalued attribute?
multi-valued attribute: Consider a PERSON entity. The person it represents has (one) SSN, (one) date of birth, (one, although composite) name, etc.
What is the model of an atom?
Key Takeaways: Model of the Atom An atom is a building block of matter that cannot be broken apart using any chemical means. Nuclear reactions can alter atoms. The three parts of the atom are protons (positively charged), neutrons (neutral charge), and electrons (negatively charged).
What are the different types of atomic models?
Ans.1 Dalton’s Model of the Atom, J.J Thomson’s Model of Atom, Rutherford’s Atomic Model, and Neil Bohr’s Atomic Theory. Q.2 What is the most accurate atomic model?
What are the five basic principles of atomic theory?
His theory has five basic principle as following points: All mater contains very small particles which are called atoms. He belived that atoms has the small shape and solid spheres form. He also said that atoms have various motions Atom can not be destructed and changed. The atoms in element can not be created, destroyed, divided or transformed.
What are some examples of atoms in chemistry?
Here are some examples of atoms: Neon (Ne) Hydrogen (H) Argon (Ar) Iron (Fe) Calcium (Ca) Deuterium, an isotope of hydrogen that has one proton and one neutron Plutonium (Pu) F-, a fluorine anion Protium, an isotope of hydrogen