what are rules for using the er model effectively? course hero

What is an ER model?

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.

How to create an ER diagram?

Below points show how to go about creating an ER diagram. Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly. Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship.

Who invented the enterprise resource model (ER)?

Although many solutions were proposed and discussed none were widely adopted. Peter Chen is credited with introducing the widely adopted ER model in his paper “ The Entity Relationship Model-Toward a Unified View of Data “. The focus was on entities and relationships and he introduced a diagramming representation for database design as well.

What is primary key in ER diagram?

Primary Key is one of its attributes which helps to identify its member. In a weak entity set, it is a combination of primary key and partial key of the strong entity set. In the ER diagram the relationship between two strong entity set shown by using a diamond symbol.

How to draw an ER diagram?

How to Draw ER Diagrams 1 Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly. 2 Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship. 3 Add attributes for entities. Give meaningful attribute names so they can be understood easily.

What is an attribute in ER?

An attribute is a property, trait, or characteristic of an entity, relationship, or another attribute. For example, the attribute Inventory Item Name is an attribute of the entity Inventory Item. An entity can have as many attributes as necessary. Meanwhile, attributes can also have their own specific attributes. For example, the attribute “customer address” can have the attributes number, street, city, and state. These are called composite attributes. Note that some top level ER diagrams do not show attributes for the sake of simplicity. In those that do, however, attributes are represented by oval shapes.

What are the elements of an ER diagram?

There are three basic elements in an ER Diagram: entity, attribute, relationship. There are more elements which are based on the main elements. They are weak entity, multi valued attribute, derived attribute, weak relationship, and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to further define ...

What is it called when an attribute has more than one value?

If an attribute can have more than one value it is called a multi-valued attribute . It is important to note that this is different from an attribute having its own attributes. For example, a teacher entity can have multiple subject values.

What is a recursive relationship?

Recursive Relationship. If the same entity participates more than once in a relationship it is known as a recursive relationship . In the below example an employee can be a supervisor and be supervised, so there is a recursive relationship. Example of a recursive relationship in ER diagrams.

What is a relationship in science?

A relationship describes how entities interact. For example, the entity “Carpenter” may be related to the entity “table” by the relationship “builds” or “makes”. Relationships are represented by diamond shapes and are labeled using verbs.

What is ER schema?

They are widely used to design relational databases. The entities in the ER schema become tables, attributes and converted the database schema. Since they can be used to visualize database tables and their relationships it’s commonly used for database troubleshooting as well.

What are the symbols in an entity relationship diagram?

Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which are rectangle, oval and diamond to represent relationships between elements, entities and attributes. There are some sub-elements which are based on main elements in ERD Diagram. ER Diagram is a visual representation of data that describes how data is related to each other using different ERD Symbols and Notations.

What is an ER diagram?

ER Diagram stands for Entity Relationship Diagram, also known as ERD is a diagram that displays the relationship of entity sets stored in a database. In other words, ER diagrams help to explain the logical structure of databases. ER diagrams are created based on three basic concepts: entities, attributes and relationships.

What is an entity set?

An entity set is a group of similar kind of entities. It may contain entities with attribute sharing similar values. Entities are represented by their properties, which also called attributes. All attributes have their separate values. For example, a student entity may have a name, age, class, as attributes.

What is the member of a strong entity set called?

The member of a strong entity set is called as dominant entity set. The member of a weak entity set called as a subordinate entity set. Primary Key is one of its attributes which helps to identify its member. In a weak entity set, it is a combination of primary key and partial key of the strong entity set.

What are the three basic concepts of an ER diagram?

ER diagrams are created based on three basic concepts: entities, attributes and relationships. ER Diagrams contain different symbols that use rectangles to represent entities, ovals to define attributes and diamond shapes to represent relationships. At first look, an ER diagram looks very similar to the flowchart.

What is the purpose of an ER diagram?

The purpose of ER Diagram is to represent the entity framework infrastructure. Entity Relationship Diagram Example.

What is an entity in a database?

An entity can be place, person, object, event or a concept, which stores data in the database. The characteristics of entities are must have an attribute, and a unique key. Every entity is made up of some 'attributes' which represent that entity.