Is schema same as ERD?
BOTH diagrams serve quite DIFFERENT purposes: ERD: to make mere mortal end-users (and business owners) UNDERSTAND the model of a given business solution; and DATA SCHEMA: a “blueprint” used by DBAs to BUILD databases, and by DEVELOPERS to CONSUME the data in that database.
What is high level ERD?
ER Model stands for Entity Relationship Model is a high-level conceptual data model diagram. ER model helps to systematically analyze data requirements to produce a well-designed database. The ER Model represents real-world entities and the relationships between them.
What is cardinality in entity relationship diagram?
Cardinality refers to the maximum number of times an instance in one entity can relate to instances of another entity. Ordinality, on the other hand, is the minimum number of times an instance in one entity can be associated with an instance in the related entity.
What is the three schema architecture?
Three-schema architecture is an idea in relational database design that breaks a database down into three different categories according to its use and structure, and to the roles played by system administrators, designers and end users.
What are high level entities?
High-level Conceptual Data Models An entity represents a real-world object such as an employee or a project. The entity has attributes that represent properties such as an employee’s name, address and birthdate. A relationship represents an association among entities; for example, an employee works on many projects.
Is the ER diagram the same as the relational schema?
The ER diagram represents the conceptual level of database design meanwhile the relational schema is the logical level for the database design. We will be following the simple rules:
How is a country represented in a relational schema?
Also, a country can have many people. To express this relationship within a relational schema we use a separate table as shown below: It is recommended to use table to represent them to keep the design tidy and clean regardless of the cardinality of the relationship.
Which is an example of an entity relationship?
Examples are a person, car, customer, product, gene, book etc. Attributes: an entity is represented by a set of attributes (its descriptive properties), e.g., name, age, salary, price etc. Attribute values that describe each entity become a major part of the data eventually stored in a database.
What are the attributes of an entity type?
Key attributes of an Entity Type Entities of an entity type need to be distinguishable. A superkey of an entity type is a set of one or more attributes whose values uniquely determine each entity in an entity set. A candidate key of an entity type is a minimal (in terms of number of attributes) superkey.