Database
A database is an organised collection
of structured data. Database software enables you to organise and store data so
that specific items of information can be retrieved easily and quickly in a
structured fashion. A database file contains one or more tables. A table is a
collection of related data about a subject (person, place or thing) and is
divided into rows and columns. Each row is a record and each column is a field.
A record is a group of related fields. A field is a data item within a record. Each
record has a key field (primary field) which uniquely identifies a record.
Using a key field can speed up operations such as searching and sorting. A key
field also allows tables to be linked. Linking tables enables a database to
create queries that retrieve data from several tables. A flat-file database has
only one table, whereas a relational database has several linked tables. An
index is a table that contains two columns: one column stores a sorted list of
the values in the field or fields being indexed and the second stores a
pointer, which gives the location of each record in the table. The key field is
always indexed and you can choose to index other fields. Indexes can speed up
operations such as queries. Each field is automatically assigned default field
properties depending on the data type. The field properties, which can be
changed, determine how a field is stored, how it works and how it is displayed. 
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