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BTEC level 3 IT Unit 18 Database Design
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Complete assignment. Grade D*
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P1: The features of a relational databaseFeatures
Entities
When data is captured, it is stored in entities. These can be tables
containing data based the importance of a thing or an object. For
example, in an organisation, they would have a database with tables
containing data such as customer details like name, surname, address,
mobile number etc.
Primary Keys
Primary keys are unique numbers given to each individual in a
database (or if it is to do with stocking, a primary key would be given
to each item on the stock list). They are given in order to identify a
person or product, so for example when customers are entered into a
database, as they are each given unique numbers, if a customer were
to ring in and request information, they would be asked to give their
primary key number to identify them (instead of having the
organisation to search for the hundreds of people with the same names
as them).
Foreign Keys
Foreign keys link tables together. A primary key would be used in one
table, and if used in another table, as it will be identical, once linked
together they will be known as foreign keys. For example, if another
table is made using new and current primary keys, it is best that if one
item (or customer) in the table remains with the primary key in which
they were issued (which then makes it a foreign key in the new table
as it would be linked to where it came from) so that no confusion
could be made, and also so that a second key is not made for that
same item.
,Data Redundancy
This occurs when data that is inputted into a database has been
entered in more than one table within the database, having the data
being considered as duplicated data. It is something that most
organisations tend to avoid, as it means that duplicated data would
need to be updated all at the same time in order to all be accurate. For
example in an organisation that makes and sells clothes, if data
redundancy happens, it could result in loss of money, and can be time
consuming to deal with as it means updating each and every
duplicate. Data redundancy also wastes quite an amount of space.
Attributes
Data Types
When creating tables in a database, users are given the option to add
further description to what they are inserting into their cells, for
example apart from field names and data types, you can choose from
having text, number, date/time, currency, an AutoNumber, yes/no,
OLE object, lookup wizard or a hyperlink. This can be done mostly to
define exactly what is going to be inputted in each cell, for example
by having the date/time selection; the date would need to be in this
format: 00/00/0000. So if a user were to input 29th April 1999, it will
be false. By having these data types, it saves memory.
Other Field Properties
, Data that is to be inputted into fields should always be valid, or the
database wouldn’t be reliable. In order to validate data that is
inputted, an input data should be used, for example in a field that
requires an address to be filled in, an address would require both
numbers and letters to be filled into that field, so by inserting “LL99”
into the input mask it means that the user can use both alphabetic
characters and numeric character in order to type in their address,
therefore making it valid.
One-to-One One-to-Many Many-to-Many
A one to one relationship is by having one table linked to another
table in a database. One to many relationships would be if one table is
linked to more than one tables in a database, and a many to many
would be if many tables in a database are linked to many other tables
in the database. For example, in a business which sells products,
customers can order almost each item in a stock table, and with stock
it can contain more than one fields in the database linked to one other
table, making it a one to many relationships.
Normalisation
This is the process of having data in the database be organised by
having it analysed and rearranged into tables. By arranging data into
tables, you can define them by creating relationships between them.
With normalisation it can avoid data redundancy and would take up
less space in the database.
Attributes
Businesses can use attributes to help them. This can be done by
identifying the most important factors. For example, ‘Name, address,
postcode etc.’ and then putting them in entities.
Data Types
Text/Alphanumeric
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