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DBMS → Introduction to DBMS 36

Concurrent access anomalies in file systems occur because
Multiple users update data simultaneously without coordination leading to inconsistency
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Security problem in file processing systems is that
Enforcing access constraints is difficult in ad hoc file-based systems
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A database-management system (DBMS) is
A collection of interrelated data AND set of programs to access those data
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Which symbol represents an entity in ER notation?
Rectangle
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Which symbol represents a relationship in ER notation?
Diamond
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A derived attribute is shown as
Dashed ellipse
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A multi-valued attribute is shown as
Double ellipse
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A weak entity is represented by
Double rectangle
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The identifying relationship of a weak entity uses
Double diamond
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Composite attribute in ER has
Ellipse with sub-component ellipses branching off
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A unary (recursive) relationship has degree
1
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A binary relationship has degree
2
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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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DBMS → Views 1

The purpose of view level abstraction is to
Simplify user interaction by showing only relevant parts of database
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DBMS → Transactions 1

Atomicity problems in file systems occur because
Operations like fund transfers may be partially completed during failures
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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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