Entity Relationship Modeling
A person, place, object, event or concept in the user environment about which the
organization wishes to maintain data.
Entity
An entity that has an independent existence and generally represents real-world objects such as persons and products.
Strong Entity
This is the type of Entity that cannot exist except with an identifying relationship (a diamond with a double line) with an owner (regular) entity type.
Weak Entity
Type of entity that is formed from many-to-many relationships between other entity types.
Associative Entity
A property or characteristics on an entity type that is of
interest to the organization.
Attribute
A type of attribute that can hold only one value.
Single Attribute
Composed of several attributes.
Composite Attribute
This type of attribute can hold several values.
Multivalued Attribute
Hold values from the result
of existing attributes.
Derived Attribute
a pattern, plan,
representation, or description
designed to show the structure
or workings of an object,
system, or concept.
Model
a graphical representation of an
entity-relationship model.
Entity-Relationship Diagram
A collection of similar entities. Similar to a class in object-oriented languages.
Entity Set
It connects two or more entity sets. It is represented by a diamond, with lines to each of the entity sets involved.
Relationships
a type of relationship in databases where multiple records in one table can be related to multiple records in another table.
Many to Many Relationship
A type of relationship where multiple records in one table are associated with a single record in another table.
One to many Relationship
a type of relationship where each record in one table is associated with exactly one record in another table, and vice versa. This means that for every record in Table A, there is one and only one corresponding record in Table B.
One to One Relationship
a relationship between a strong and weak
entity wherein the very existence of the
weak entity depends on the strong one.
Identifying Relationship
refers to the number of entity sets that participate in that
relationship
Degree of a relationship
Relationship between the entities
of a single entity set.
Unary Relationship
relationship between the entities of
two entity sets.
Binary Relationship
simultaneous relationship among the
entities of three entity sets.
Ternary Relationship
expresses whether the relationship
is optional or mandatory.
Optionality
expresses the maximum number of
relationships.
Cardinality
It is another term for table. A structured set of data that is organized into rows and columns.
Relation
a special column (or a combination of columns) in a database table that uniquely identifies each record (row) in that table. It ensures that every row has a unique identifier and that no two rows have the same primary key value.
Primary Key