Section 10 DBs Flashcards
What is a relational database?
A method of creating a database using tables of related data, with relationships between the tables
What is a table?
A method for implementing on entity and attributes as a group of related data.
What is an entity?
An object about which data will be sorted
What is an attribute?
A characteristic or piece of information about an entity, which would be stored as a field in a relational database.
What is a primary key?
A primary key is an attribute that can be used to uniquely identify every resort in that table
What is an entity identifier?
An attribute which can uniquely identify each instance of an entity
What is a foreign key?
An attribute in a table that is a primary key in another table and used to link tables together
What is normalisation?
The process of ensuring that a relational database is structured efficiently and ensuring all data is atomic
What is the first normal form?
First normal form I’d achieved by ensuring that a table does not contain repeating attributes and that all of the data in the table is atomic.
What is second normal form?
Second normal form is achieved by ensuring that the data is atomic and by removing the attributes that depend upon part but not all of the primary key
What is third normal form?
Third normal form is achieved by ensuring the data is in second normal form then removing non key attributes that depend on other non key attributes by creating additional tables
What is SQL
Structured query language (SQL) is a specialised programming language for manipulating databases.
What is a table?
A table is a method for implementing an entity and attributes as a group of related data.
What is syntax?
Syntax I’d the rules of how words are used within a given language.
What is a query?
A query is a search or sort carried out on data that retrieved the answer to a question
What is a database management system?
It is software that enables the management of all aspects of a database including adding, updating and querying data
What is a client sever database?
It is a way of implementing a database where the database is put into a server and various users can access it from their workstation. The processing, eg running a query, will take place on the database
What is one issue with concurrent access on a shared database?
One common problem with this type of database is that when multiple users try to access/modify the same data at the same time.
What is a record lock?
A record lock is one way to prevent concurrent issues is, it essentially puts a temporary lock on the data that is being edited so that no other users can edit that data at the same time
What is serialisation
Serialisation is the process of only allowing one transaction to be executed at a time. By using the DBMS ensures that each transaction happens after each other.
What is timestamp ordering?
Every database transaction gets a read and write timestamp.
Used to ensure serialization by sequencing transactions.
Prevents concurrency issues by determining the last action on a record.
DBMS decides whether to execute a transaction based on timestamps.
What is commitment ordering?
Orders commands based on when they were made and their impact.
Prevents deadlocks by blocking conflicting transactions until dependencies are resolved.
Uses a transaction dependency graph for execution order.
