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DBMS → Introduction to DBMS 33

A ternary relationship has degree
3
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ISA hierarchy in ER represents
Specialization and generalization inheritance
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Generalization is which process?
Bottom-up: combining similar entities into a superclass
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Specialization is which process?
Top-down: dividing superclass into specialized subclasses
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Disjoint ISA constraint means
Entities can be in AT MOST ONE subclass
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Overlapping ISA constraint means
Entities can belong to MULTIPLE subclasses simultaneously
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Total completeness means
Every superclass entity MUST belong to at least one subclass
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Aggregation in ER treats
A relationship set as an abstract entity to participate in another relationship
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In min-max notation (0,N) on a relationship side means
Zero (optional) to many
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In min-max notation (1,1) means
At least one and at most one (mandatory, exactly once)
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Weak entity PK is formed by
Discriminator plus owner entity's primary key
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Partial participation means
Only SOME entity instances participate in the relationship
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A regular entity has
Its own key attribute and exists independently
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M:N cardinality means
Each entity can relate to many instances on the other side
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Students enroll in courses is what cardinality?
M:N
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Employee assigned one parking space is what cardinality?
1:1
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Key attribute in ER is shown with
Underlined attribute name
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An associative entity (junction entity) is used when
M:N relationship needs its own attributes
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M:N relationship requires in relational schema
Junction table with FKs to both entity tables
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Relational Algebra is
Procedural: specifies what and HOW to get data
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Selection operator σ selects
Rows satisfying a condition from a relation
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Projection operator π extracts
Specific columns (attributes) from a relation
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For Union R∪S to be valid R and S must be
Union-compatible: same degree and compatible domains
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R∩S returns
Tuples present in BOTH R and S
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R−S returns
Tuples in R that do NOT exist in S
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Cartesian product R×S produces
All possible combinations of tuples from R and S
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Renaming operator in relational algebra is
ρ
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Division R÷S is useful for
Universal quantification queries (for all/every conditions)
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Five basic RA operators are
σ,π,∪,−,× (selection,projection,union,difference,cross-product)
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If |R|=5 rows and |S|=4 rows, R×S has
20 rows
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R∩S expressed using basic operators equals
R−(R−S)
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SQL stands for
Structured Query Language
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SELECT retrieves
Data from one or more tables
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DBMS → ER Model 2

ER diagrams are created in which design phase?
Conceptual design
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ER diagram to relational schema: each entity becomes
A table (relation)
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DBMS → Joins 4

Theta join R⊲⊳θS equals
σθ(R×S)
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Equijoin uses which condition operator
= (equality)
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Natural join joins on
All attributes with same name in both relations
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Anti-join R▷S returns
Tuples in R that have NO matching tuple in S
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DBMS → SQL Basics 1

WHERE clause filters
Individual rows BEFORE grouping based on condition
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