DBMS MODULE 2

Data Model

Conceptual tool to describe data, data relationships, and data semantics.

Entity

Object that exists and is distinguishable from other objects.

Attribute

Property of an entity.

Entity set

Set of entities of the same type sharing the same properties.

Domain

Set of permitted values for an attribute.

Relationship

Association among several entities.

EER model

Enhanced ER model supporting additional semantic concepts.

Superclass

Entity type with one or more distinct subgroups.

Subclass

Entity type sharing common and unique attributes compared to other subclasses.

Attribute inheritance

Subclass inherits attributes and relationships of superclass.

Subclass relationship

One-to-one relationship between superclass and subclass.

Specialization

Top-down process of creating subclasses from a superclass.

Generalization

Bottom-up process of creating a superclass from multiple subclasses.

Participation constraint

Rule deciding if superclass instance must be member of subclass.

Total participation

Every superclass instance must belong to at least one subclass.

Partial participation

Superclass instance may or may not belong to any subclass.

Disjoint constraint

Defines whether instance can belong to multiple subclasses or not.

Disjoint rule

Instance in one subclass cannot belong to another subclass.

Overlap rule

Instance may belong to multiple subclasses.

Subclass discriminator

Attribute used to determine membership of subclasses.

Strong entity

Entity with a primary key that can exist independently.

Weak entity

Entity that cannot be uniquely identified without a strong entity.

Partial key

Attribute of a weak entity used with owner key to uniquely identify it.

Simple attribute

Indivisible attribute (atomic).

Composite attribute

Attribute composed of multiple subparts.

Single-valued attribute

Attribute with one value per entity.

Multi-valued attribute

Attribute with multiple values per entity.

Derived attribute

Attribute whose value is derived from other attributes.

Relationship set

Set of relationships of the same type.

Degree of relationship

Number of participating entity sets.

Unary relationship

Relationship involving one entity set.

Binary relationship

Relationship involving two entity sets.

Ternary relationship

Relationship involving three entity sets.

N-ary relationship

Relationship involving more than three entity sets.

Mapping cardinality

Relationship constraints like 1:1, 1:N, N:1, M:N.

Total participation (ER)

Every entity must participate in the relationship.

Partial participation (ER)

Entity participation in relationship is optional.

Relation

Table with rows and columns in relational model.

Tuple

Row in a relation.

Attribute (relational)

Column in a relation.

Relation schema

Structure: relation name + list of attributes.

Cardinality

Number of rows in a relation.

Superkey

Set of attributes uniquely identifying a tuple.

Candidate key

Minimal superkey.

Primary key

Chosen candidate key for unique identification.

Foreign key

Attribute referring to primary key of another relation.

Referential integrity

Rule ensuring FK matches PK in referenced relation.

Specialization (EER)

Top-down creation of specific lower-level entity types.

Generalization (EER)

Bottom-up merging of entity types into a higher-level type.

Aggregation

Treating relationship as entity to model relationship between relationships.

Mapping strong entity

Table with same attributes; primary key retained.

Mapping weak entity

Table includes strong entity key + partial key.

Mapping composite attribute

Flatten composite into multiple atomic attributes.

Mapping multi-valued attribute

Create separate table storing PK + attribute value.

Mapping many-to-many

Create table with PKs of both entities + relationship attributes.

Mapping one-to-many

Add foreign key to the “many” side.

Mapping one-to-one

Add FK to either entity table.

Mapping weak relationship

Relationship table may be redundant because dependent table already stores required keys.

Specialization mapping Method 1

Create table for superclass + tables for each subclass containing PK of superclass.

Specialization mapping Method 2

Create table for each subclass with inherited + local attributes.

Mapping aggregation

Create table with keys of all participating entities + attributes of aggregated relationship.