5. Databases Flashcards
What is a database?
A persistent organised store of data.
Why is a database described as “persistent”?
- A database is a non-volatile store of data on a secondary storage medium such as a hard disk.
- This makes it different to an array.
What is data handling software used for?
Creating, maintaining and interrogating a database.
How can data handling software be created?
• Using an off-the-shelf product such as Microsoft Access
OR
• Creating the database itself in one of these products and then using a high level programming language to create a customised, form based, front-end application that does exactly what is needed
Why must a database by maintained?
Because the quality of information you get out is only as good as the information you put in (GIGO).
What is GIGO?
Garbage In, Garbage Out - The idea that the quality of information from a database is only as good as the quality you put in.
Revise the operations on a database.
Pg 66 of textbook -> Diagram
What is data duplication/redundancy?
Where the same data is stored more than once, unnecessarily.
What is data inconsistency?
Where different versions of the same data have different values because different versions have been stored and updated differently.
What is the important statement about keeping data in two different places?
Data duplication leads to data inconsistency.
What is the DBMS?
Database Management System - The system that separates the applications from the data and provides features that allow database systems to be created, interrogated and maintained.
What is the problem with different departments of a shop using the same database without a DBMS?
- Although the data is consistent, it introduces security issues and the applications are too closely linked to the data.
- This means that if one department changed something, it would affect the programs the other departments were using.
- Separation is needed.
What is used to separate programs from data?
A DBMS.
What is program-data independence?
Where the applications that use a shared database are separated from the actual data by a DBMS. Changes can be made to one application without it affecting another.
What are views of a database?
A feature of a DBMS that provides each application (e.g. the training department) or user with specific access, editing rights and view of the database.
What are some key features of a DBMS?
- Separation between applications and database
- Allows multiple applications to use a single database
- Manages multiple applications trying to edit the same record at the same time (usually makes it read only for the second application)
- Provides appropriate views of the database to different users
- Provides security in terms of views and access rights
- Enables creation of the relational database structure
- Allows applications to query/interrogate the database
- Creates reports based on queries
- Allows certain applications to edit and maintain database
- Automatic back-up
Give an example of a DBMS.
Microsoft Access
What is a flat file database?
A persistent organised store of data where data is stored in a single file organised into fields and records. (e.g. A spreadsheet)
What is a relational database?
A persistent organised store of data where data is stored as a collection of related tables to minimise data redundancy.
What is the problem with a flat file database?
It is easy to get data inconsistency.
What are the benefits of reducing data duplication?
- Reduces the risk of data inconsistency
- Makes maintaining the database much easier
- Reduces the size of the database
What is an entity?
A category of, for example, person, object or event about which data is stored in a database, and which corresponds to a table in the relational database. (e.g. Cars in a garage database)
What do we use to create links between tables in a database?
A DBMS.
What is a table?
A collection of data organised into records and fields within a relational database. A table represents a real world entity.
What is the relationship between entities and tables?
Each table is a representation of a real world entity.
What is a record?
A single entry into a database, containing all of the attributes of one instance of an entity. (i.e. A horizontal row)
What is a field?
A column in a database, representing one particular entity of an entry. (Basically, the headings at the top of the table)
What is the primary key?
A field in a table that uniquely identifies a record.
What is the foreign key?
A field in one table that is the primary key in another table and is used to create a relationship between those two tables.
What is important about the primary key?
Every record must have a different value in this field to make it unique.
What is a relationship?
- The logical connection created between two tables using a primary and foreign key pair.
- It allows related data about a record to be accessed from another table.
What sort of relationships are there?
- One-to-one
- One-to-many
- Many-to-many
What is a form?
An interactive window used for data entry into a database. (Input)
What is validation?
A check made by the computer to make sure the data is sensible and conforms to the rules set out by the programmer.
What is verification?
A check to ensure that data has been input correctly. For example, asking the user to reader to read the data they have input and check it is correct. Or
Give two examples of verification.
- Asking the user to re-read the data and confirm it is correct
- The data has to be entered twice and one version is compared against the other to make sure it is the same
What is a query?
- A feature of a DBMS that allows the database to be interrogated.
- It selects encores from the database based on specific criteria.
What are some logic operators and when are they used?
NOT, AND, OR. Used in complex criteria in queries.
What is a data type?
The sort of data that can be stored in a variable or field in this case.
Give some examples of validation checks.
- Range check
- Type check
- Length check
- Existence check
- Presence check
- Format check
What is a type check?
A check to see if the data type is correct.
What is an existence check?
A check to see whether a product or customer actually exists.
What is a presence check?
A check to make sure that some data has been entered (i.e. No blank fields)
What is a format check?
A check to see that the format of a postcode, email address, etc. is appropriate.
What is the difference between validation and verification?
Validation checks whether the data fits some criteria, whereas verification asks the user to double-check their input.
What takes priority, AND or OR?
AND
What are the features of a good report?
- Dated
- Clear title
- Good layout with clear columns
- Page numbers
- Sorted in a logical sequence
What is a report?
A snapshot in time of the data from a database that can be printed. It is formatted and may be sorted or grouped. (Output)
What is a module?
A section of code within a DBMS that allows the user interface to be tailored.
