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Unit 18 - P1, M1

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Rashid Al-awdi

on 20 May 2015

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Transcript of Unit 18 - P1, M1

Unit 18 - P1, M1
What is a relational database?
The relational database was created by IBM's E.F. Codd in 1970. It is a collection of data presented in a table in a structured and efficient manner. Using relational databases enables data to be accessed and/or altered in an easy and accessible way. It places data in tables and categories and saves time and effort when trying to access whatever data the user may need.
How can data be customised and validated when being stored or entered in to a database
Data types
Text  Used to input chatactersMemo  Long uses to text (sentences and paragraphs) Number  Used for numbersDate/Time  Calendar and clock dataCurrency  Money values There are more data types including AutoNumber, Yes/No, OLE Object and Hyperlink
Field properties: Field Size, Format, Input Mask, Caption, Default value, Validation Rule, Validation Text etc
Validation rules
This limits what can be inputted in to a table field. For example for a field that asks for Title, you can validate it saying “Enter Mr, Miss, Ms, Mrs”
Validation rules in terms of attribute restricts the type of data that can be entered. For example different fields accept different types of data types like currency only accepts numerical values and name only accepts text values
Benefits of a relational database

It allows you to organise data in the most efficient manner with little effort needed to access any data needed, even over multiple databases.
Reduced data storage
The amount of space needed is relatively miniscule as much less space is used when storing data as well as it being better to input information; this also adds to the aforementioned benefit of efficiency.
Avoids error
As relational databases uses validation rules, it ensures the integrity of the data, minimising the risk of any human errors that could possibly occur; through efficient updating, searching, sorting and reporting all possible or made errors.
(M1) Explain referential integrity and the purpose of primary keys in building the relationships between tables
Key features of a relational database:
The key features of a relational database are:
they are the tables in the database that hold information about the objects being recorded, for instance customers or runners or even pupils of a school.
these are presented in the columns or fields of the table; they are the properties of an entity, particular information of the entities that truly differentiates the entities at hand. An example would be names, addresses and ages of pupils in a school.
these are of the utmost importance as it this that links tables to each other. A failure to implement the correct relationship could be detrimental to the database and lead to inefficiency, errors and reduce the overall functionality of the database.

Three types of relationships
There are three types of relationships you need to know that can be made between tables. The relationships are:
this is where the tables that are being linked only one record on either side of the relationship. The primary key would only relate to one or no record in the table.Each primary key value relates to only one (or no) record in the related table.
this is where the primary key table contains only one record that relates to either many, one or no records in the related table.
this is where each record in tables being linked can relate to any number of records or even no records in the other table.

Primary and foreign keys
Primary Key
It's is a unique data item that enables you to identify any piece of record.
Foreign Key
When a primary key is duplicated into another table, thus creating a relationship, it is then known as a foreign key. This aids in the process of retrieving data in the fastest and most efficient way.
Referential integrity
is a feature in the relational database ensures the consistency of relationships between tables. When one table in linked to another through a foreign key, referential integrity would not permit a record being added to the table that holds the foreign key without a matching record being added to the attached table.

Purpose of primary keys
Primary keys are unique data items that enables you to identify any piece of record. A table can only have one primary key and it usually the 'ID'. It enables you identify someone easy and in a fast way, for instance, you can identify a student in database full of students with just their ID rather than their actual details.

Building of relationships
Foreign keys are used to link tables and create relationships. It is through the use of a foreign keys that referential integrity is ensured. So when a change is made on one table, the same changes will be made on the tables linked to it through a foreign key.
Thank you for watching.
Relational databases are:
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