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# Relational Algebra in Systems Analysis and Design

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@EasyCognition2272

### What is the process of defining a set of subclasses of a superclass called?

• Specialization (correct)
• Composition
• Generalization
• Aggregation
• ### What type of constraint applies to a specialization/generalization where every subclass has only one superclass?

• Disjointness Constraint
• Condition-Defined Constraint
• Completeness Constraint
• Single Inheritance Constraint (correct)
• ### What is the result of mapping an ER schema?

• Entity set
• Relational schema (correct)
• EER diagram
• ER diagram
• ### What is the process of creating a superclass from a set of subclasses called?

<p>Generalization</p> Signup and view all the answers

### What type of constraint applies to a specialization/generalization where a subclass can be a subclass of more than one superclass?

<p>Multiple Inheritance Constraint</p> Signup and view all the answers

### What is the step in ER-to-Relational mapping that involves mapping of superclass/subclass relationships?

<p>Step 8</p> Signup and view all the answers

### What is the term for a subclass that inherits all attributes of the entity as a member of the superclass?

<p>Subclass</p> Signup and view all the answers

### What type of relationship is formed when a subclass is a subclass of more than one superclass?

<p>Lattice</p> Signup and view all the answers

### What is the term for a subclass that has further subclasses specified on it?

<p>Subclass</p> Signup and view all the answers

### What is the purpose of ER-to-Relational mapping?

<p>To map an ER schema into a relational schema</p> Signup and view all the answers

## Study Notes

### Relational Algebra

• Enables users to specify basic retrieval requests
• Operations produce new relations that can be further manipulated
• Fundamental operations: • Union (∪) • Set difference (-) • Selection (σ) • Projection (π) • Cartesian product (X)
• Additional operations: • Rename (ρ) • Intersection (∩) • Join • Division (÷)
• Type compatibility requirements: • Same degree • Corresponding attributes defined over the same domain

### SQL

• Language for expressing queries on relations
• Based on relational algebra for sets and bags
• Supports creation and modification of relations
• Examples of SQL queries: • CREATE TABLE R () • INSERT INTO R VALUES (v1; … ; vn) • DELETE FROM R WHERE C • UPDATE R SET A = v WHERE C • SELECT .. FROM … WHERE…

### Relations

• A two-dimensional table
• Attributes ≈ column names
• Tuples ≈ rows (not including header row)
• Database ≈ collection of relations
• Relation characteristics: • Each relation has a distinct name • Each attribute has a distinct name • Values of an attribute are from the same domain • Each tuple is distinct • Entity degree is the number of fields/attributes in schema • Entity cardinality is the number of tuples in relation

### Relational Model Integrity Constraints

• Conditions that must hold on all valid relation instances
• Three main types: • Key constraints • Entity integrity constraints • Referential integrity constraints • Semantic integrity constraints
• Specified when schema is defined
• Checked when relations are modified

### Relational Data Model Operations

• Two categories: • Retrieval operations (extract information) • Update operations (cause relation state changes)

### EERD (Enhanced ER or Extended ER)

• EER diagrams extend ER diagrams to represent additional subgroupings
• Subclasses or subtypes
• Superclass/subclass relationships
• Inheritance: • All attributes of the superclass • All relationships of the superclass
• Specialization: defining subclasses of a superclass
• Generalization: reverse of specialization process

### Constraints on Specialization and Generalization

• Three basic constraints: • Condition-Defined Constraint • Disjointness Constraint • Completeness Constraint

### Lattices & Shared Subclasses

• A subclass may have further subclasses specified on it
• Forms a hierarchy or lattice
• Hierarchy: every subclass has only one superclass (single inheritance)
• Lattice: a subclass can be subclass of more than one superclass (multiple inheritance)

### ER-to-Relational Mapping

• Step 1: Mapping of Regular Entity Types
• Step 2: Mapping of Weak Entity Types
• Step 3: Mapping of Binary 1:1 Relation Types
• Step 4: Mapping of Binary 1:N Relationship Types
• Step 5: Mapping of Binary M:N Relationship Types
• Step 6: Mapping of Multi-valued attributes
• Step 7: Mapping of N-ary Relationship Types
• Step 8: Mapping Super class/ Sub class relationship

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## Description

Learn about relational algebra operations in systems analysis and design, including retrieval requests and relation manipulation. Based on Dennis, Wixom, & Roth's 3rd Edition.

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