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Questions and Answers
Match the following terms with their definitions:
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:
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:
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:
Match the following statements with the correct representation:
Match the following relational model components with their descriptions:
Match the following relational model components with their descriptions:
Match the following relational integrity terms with their meanings:
Match the following relational integrity terms with their meanings:
Match the following database terms with their definitions:
Match the following database terms with their definitions:
Match the following properties of relations with their characteristics:
Match the following properties of relations with their characteristics:
Each cell in a table can contain multiple values.
Each cell in a table can contain multiple values.
Primary Key is selected from Alternate Keys in a relation.
Primary Key is selected from Alternate Keys in a relation.
Order of columns has significance in a relation.
Order of columns has significance in a relation.
Null represents a value that is the same as zero or spaces.
Null represents a value that is the same as zero or spaces.
SQL and QBE are two main relational languages used to query databases.
SQL and QBE are two main relational languages used to query databases.
Entity Integrity states that in a base table, every column of a primary key can be null.
Entity Integrity states that in a base table, every column of a primary key can be null.
Relational Integrity Business Rules are rules that define or constrain some aspect of the organization.
Relational Integrity Business Rules are rules that define or constrain some aspect of the organization.
Referential Integrity ensures that a Foreign Key (FK) must always match a Primary Key (PK) value in another table.
Referential Integrity ensures that a Foreign Key (FK) must always match a Primary Key (PK) value in another table.
A Tuple in the relational data model refers to a column of a relation.
A Tuple in the relational data model refers to a column of a relation.
The Relational Database is a collection of denormalized relations with similar relation names.
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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