8.1 Databases.concepts Flashcards
What is a database?
A structured collection of data items that can be accessed by different application programs.
What is a relational database?
A database where data items are linked by internal pointers.
What is a table in a database?
A group of similar data with rows for each instance of an entity and columns for each attribute.
What is a record in a database?
A row in a table representing one instance of an entity.
What is a field in a database?
A column in a table representing an attribute of the entity.
What is a tuple in a database?
One instance of an entity, represented by a row in a table.
What is an entity in a database?
Anything that can have data stored about it, such as a person, place, event, or thing.
What is an attribute in a database?
An individual data item stored for an entity, like a name, address, or date of birth.
What is a candidate key?
An attribute or smallest set of attributes where no two tuples have the same value.
What is a primary key?
A unique identifier for a table, which is a special case of a candidate key.
What is a secondary key?
A candidate key that serves as an alternative to the primary key.
What is a foreign key?
A set of attributes in one table that refers to the primary key in another table.
What is a relationship in a database?
A situation where a table has a foreign key that refers to a primary key in another table.
What is referential integrity?
A database property ensuring no foreign key values exist without matching the corresponding primary key.
What is an index in a database?
A data structure built from one or more columns in a table to speed up searching.
What is an Entity-Relationship (E-R) model or diagram?
A graphical representation of a database and the relationships between entities.
What is normalisation in a database?
The process of organising data into two or more tables and relationships to minimise redundancy.
What is First Normal Form (1NF)?
A relational database status where entities do not contain repeated groups of attributes.
What is Second Normal Form (2NF)?
A database in 1NF where non-key attributes depend entirely on the primary key.
What is Third Normal Form (3NF)?
A database in 2NF where all non-key attributes are independent of each other.
What is a composite key?
A set of attributes that together form the primary key to uniquely identify a table record.
What is a file in computing?
A collection of items of data, often structured as records made up of fields containing data about the same ‘thing’.
What is a data item?
An individual element of data within a record or field.
How does the organisation of records in a program affect data processing?
Records can be fixed or variable in length and may contain information about their structure, requiring programs using them to follow the same structure.
Why can record structure cause issues in file-based systems?
If one program changes the structure, all other programs using the file must be updated; failure to do so can cause data handling errors.
What is one limitation of a file-based approach?
Storage space is wasted due to data duplication and redundancy.
How can data inconsistency arise in a file-based approach?
If one application alters data and another does not, the data becomes inconsistent.
Why is data independence limited in a file-based approach?
Enquiries depend on the data structure and software used, making the data not truly independent.
How does the BCS Glossary of Computing define a database?
A large collection of data items and links between them, structured for access by different applications programs.
How does CJ Date define a database?
An electronic filing cabinet allowing tasks like adding, inserting, retrieving, updating, and cross-referencing data.
What is a simple definition of a database?
A structured collection of data items that can be accessed by different applications programs.
How is data typically structured in a database?
As a collection of records, where each record contains fields with data about the same ‘thing’.
What is a relational database?
A database where data items are linked by internal pointers.
List one benefit of the database approach regarding storage.
Data items are stored only once, reducing redundancy and saving storage space.
How does the database approach ensure data consistency?
Data altered in one application is automatically available in other applications.
Why is data independence a benefit of the database approach?
Enquiries do not depend on the data structure or software used, allowing flexibility in data access.
What is a table in a relational database?
A group of similar data with rows for each entity instance (tuples) and columns for each attribute (fields).
What is a record (or tuple) in a relational database?
A row in a table representing one instance of an entity.
What is a field (or attribute) in a relational database?
A column in a table representing a single data item stored for an entity.
Define ‘entity’ in the context of a relational database.
Anything that can have data stored about it, such as a person, place, event, or object.
How is data consistency maintained in a relational database?
By controlling or automating updates and minimising duplicate data copies through pointers (keys).
What is a candidate key?
An attribute or the smallest set of attributes that uniquely identify a tuple in a table.
What is a primary key?
A unique identifier for a table; it is a special case of a candidate key.
What is a secondary key?
A candidate key that serves as an alternative to the primary key.
What is a foreign key?
An attribute in one table that refers to the primary key in another table, creating a relationship.
How is a relationship formed in a relational database?
When a table contains a foreign key that refers to a primary key in another table.
What is referential integrity?
Ensuring that every foreign key value in a table matches a primary key value in the referenced table.
What are the types of relationships in a relational database?
One-to-one (1:1), one-to-many (1:m), many-to-one (m:1), and many-to-many (m:m).
What is the purpose of an index in a relational database?
To speed up searching for data by creating a data structure from one or more columns in a table.
What is the purpose of an Entity-Relationship (E-R) diagram?
To provide a visual representation of how entities in a database are related.
What does the term ‘cardinality’ mean in an E-R diagram?
It defines the type of relationship and whether it is mandatory or optional between entities.
Give an example of an optional relationship in an E-R diagram.
The relationship between desk and employee is optional (zero or one) since some desks might be unassigned.
Give an example of a mandatory relationship in an E-R diagram.
The relationship between mother and child is mandatory (one or many) because every mother must have at least one child.
What is the purpose of normalisation in database design?
To reduce data redundancy and ensure data integrity in a relational database.
What happens if a database is not normalised?
It will be larger, harder to update, and more difficult to extract data for queries.
What is First Normal Form (1NF)?
A state where entities do not contain repeated groups of attributes.
What is Second Normal Form (2NF)?
A state where entities are in 1NF and every non-key attribute depends on the whole primary key with no partial dependencies.
What is Third Normal Form (3NF)?
A state where entities are in 2NF, and all non-key attributes are independent of each other and only depend on the primary key.
What is the key rule for a database in 3NF?
All attributes in a table depend upon the key, the whole key, and nothing but the key.
