Information Systems & Databases Flashcards
What does FROM do?
FROM - selects the table you which to extract data from
What does SELECT do?
SELECT - takes the data from the nominated table
What does WHERE do?
WHERE - allows the user to specify what they want to search for (the search criteria)
Describe what a Flat-File Databse is?
All of the data is recorded in one table or file. Suitable for small databases. Can only manage one database at a time.
Describe what a Relational Database is.
A set of tables in a database that are linked to each other. Allows you to manage and use several separate databases. Called relational because it’s a type of database that allows you build relationships between different tables and databases.
What is a Primary Key?
It is a field that is used to uniquely identify a record in a table or relational database. The data is not replicated anywhere else in the database and it cannot be a null value (blank).
What is a Foreign Key?
A primary key in one table, but a secondary key field in another table. It’s used to establish a relationship between two or more tables. They cannot exist in a flat file database and are only found in relational databases.
A Schema or Schematic Diagram is…..
an organised plan of the entire database that shows the tables, the fileds of the tables, and the relationships between them.
What is the difference between Entities and Attributes in a schema?
Entities are the Tables in a database.
Attributes are the Fields in the tables.
A type of relationship that occurs when each record in the first entity (table) is related to exactly one record in the second entity (table)
One-to-One Relationship
A type of relationship that occurs when one record in the first entity (table) is related to many records in the second entity (table), but any record in the second entity (table) only relates to one record in the first entity (table).
One-to-Many Relationship
A type of relationship that occurs when each record in the first entity (table) is related to many records in the second entity (table), and each record in the second entity (table) is related to many records in the first entity (table).
Many-to-Many Relationship
A type of access method used when accessing a storage medium such as magnetic tape.
Sequential Access
A type of access method used when accessing a storage medium such as magnetic disk, CD’s or flash drives
Direct Access
A database that is located, stored, and maintained in a single location.
Centralised Database