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Questions and Answers
Match the following terms with their definitions:
Tuple = A record in a table Attribute = A column within a table File = A collection of records Field = A cell in a table
Match the following relational key concepts with their descriptions:
Superkey = Identifies a record uniquely within a table Candidate Key = Minimal superkey for a relation Primary Key = Selected to identify records uniquely within a table Foreign Key = Matches candidate key of another table
Match the following integrity concepts with their definitions:
Relational Integrity = Rules that define or constrain some aspect of the organization. Entity Integrity = In a base table, no column of a primary key can be null. Referential Integrity = If FK exists in a table, either FK value must match a candidate key value of some record in its home table. Business Rules = Rules that define or constrain some aspect of the organization.
Match the following statements with the correct representation:
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Match the following relational model components with their descriptions:
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Match the following relational integrity terms with their meanings:
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Match the following database terms with their definitions:
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Match the following properties of relations with their characteristics:
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Each cell in a table can contain multiple values.
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Primary Key is selected from Alternate Keys in a relation.
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Order of columns has significance in a relation.
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Null represents a value that is the same as zero or spaces.
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SQL and QBE are two main relational languages used to query databases.
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Entity Integrity states that in a base table, every column of a primary key can be null.
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Relational Integrity Business Rules are rules that define or constrain some aspect of the organization.
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Referential Integrity ensures that a Foreign Key (FK) must always match a Primary Key (PK) value in another table.
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A Tuple in the relational data model refers to a column of a relation.
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The Relational Database is a collection of denormalized relations with similar relation names.
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Study Notes
Alternative Terminology
- Relation, attribute, tuple are equivalent to table, column, record
- File, field, row are alternative terms
- Combinations of these terms are used in different contexts
Properties of Relations
- Table name is distinct from all other table names in the database
- Each cell of table contains exactly one atomic (single) value
- Each column has a distinct name
- Values of a column are all from the same domain
- Each record is distinct; there are no duplicate records
- Order of columns has no significance
- Order of records has no significance, theoretically
Relational Keys
- Superkey: a column, or a set of columns, that uniquely identifies a record within a table
- Candidate Key: a minimal superkey for a relation
- Primary Key: a candidate key selected to identify records uniquely within a table
- Alternate Keys: candidate keys that are not selected to be primary key
- Foreign Key: a column, or set of columns, within one table that matches candidate key of some (possibly same) table
Relational Integrity
- Null: represents a value for a column that is currently unknown or not applicable for a record
- Deals with incomplete or exceptional data
- Represents the absence of a value and is not the same as zero or spaces, which are values
- Entity Integrity: in a base table, no column of a primary key can be null
- Referential Integrity: if foreign key (FK) exists in a table, either FK value must match a candidate key value of some record in its home table
Relational Languages
- Two main languages: SQL (Structured Query Language), standardized by ISO
- QBE (Query-by-Example), an alternative graphical “point-and-click” way of querying a database
Relational Model
- Describes the world as “a collection of relations (or tables)”
- Data Model: an integrated collection of concepts for describing data, relationships between data, and constraints on the data
- Has three components: a structural part; a manipulative part; a set of integrity rules
RM Terminology
- Relation: table with columns and rows
- Attribute: named column of a relation
- Domain: set of allowable values for one or more attributes
- Tuple: a record of a relation
- Relational Database: a collection of normalized relations with distinct relation names
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Description
Test your knowledge on the properties of relations in databases, including attributes, tuples, table structure, and more. Explore the distinct characteristics that define a well-structured database relation.
