Databases Flashcards
Explain the properties of Serial Files:
How data is stored, the order of data and usage
- Data stored in the order it is entered.
- No order for the data is maintained.
- Used for transaction files.
All data stored on one file.
Explain the properties of Sequential Files:
How data is stored, the order of data and usage
-Data is stored in order of a key field.
-Order maintained as new records are added.
- Useful for master files.
(Was kept on magnetic tapes).
All data stored on one file.
What is an Indexed Sequential File?
An index is maintained to allow groups of records to be quickly accessed.
Define a Database:
A database is a structured, persistent collection of data..
What does persistent mean?
The data is retained after the software has finished processing it.
What are the advantages of databases over files?
- More efficient for processing.
- Reduce storage requirements.
- Avoid redundancy (duplicate data).
- Allow different users to only see relevant data.
How are databases managed?
They are managed by a DBMS (Database management system).
What does a DBMS do?
- Provides a manipulation language to access/change data.
- Provide additional security.
- Provide an interface for other programs to access data.
Give an example of a DBMS
Microsoft Access.
What do databases consist of?
Tables (entities or files) that store data in rows (records/tuples) and columns (fields/attributes).
What is an entity?
A ‘thing’ in which data is recorded for. It is the actual table in a database.
What is a record?
A record/tuple is the row in a database.
What is a field?
The column in a database.
What do queries do?
Allow the modification of data.
Give some examples of a query:
Search, add, delete and sort.
What is a Flat File database?
-A single table (all data stored in one table)
What are the disadvantages of a Flat File database?
- They are harder to query.
- Data may be duplicated (inefficient use of memory).
What is a relational database?
- A database consisting of multiple related tables
eg students, subjects studied and tutor groups.
What is the advantage of a relational database?
They are easier to query.
Explain a one to one relationship:
One record in one table is related to one record in a different table.
eg Country and Prime Minister.
Explain a one to many relationship:
One record in one table is related to many records in another table.
eg Tutor group (one record) and Students (many records).
Explain a many to many relationship:
Broken down into two one to many relationships with an extra table used between them.
eg Cars and Parts becomes Cars —-= Car Parts=—- and Part
What is used to denote a ‘many’ side of a relationship?
Three lines spreading out from a single line.
What is a primary key?
A unique identifier assigned to the field of each record in a table.
What is a Secondary Key?
An alternative identifier that can be used in a search if the primary key is unknown or impractical to use.
What is a primary key used for?
Used in the index to help quickly search the database.
How are tables linked?
Through the use of a common attribute. This attribute is a primary key of one table and a foreign key of another.
