Essay
Unit 18 - Assignment 2 - P2, P4
- Module
- Unit 18 - Database Design
- Institution
- PEARSON (PEARSON)
Unit 18 Database Design. Designing a relational database. All criteria achieved, P2, P4.
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EDEXCEL BTEC LEVEL 3 90 CREDIT DIPLOMA IN INFORMATION TECHNOLOGYAssignment 1
Introduction to Relational Databases
Joel
25/01/2017
,Contents
Task 1 -...................................................................................................................................................2
Explain the Features of a Relational Database: (P1)...........................................................................2
Explain Referential Integrity and the Purpose of Primary Keys in Building Relationships between
Tables: (M1).......................................................................................................................................3
Discuss how Potential Errors in the Design and Construction of a Database can be avoided: (D1)....3
Joel Page 1
, Task 1 -
Explain the Features of a Relational Database: (P1)
Firstly, a relational database is a database that collects data in a structured and more efficient way. A
relational database makes sure that there are no repeated values in the database. Compared to a flat
file database where the same values would be inputted multiple times, in a relational database the
information is linked through relationships so only has to be inputted once and then can be linked
directly from the original table. All needed tables can be created and then linked accordingly using
relationships. Relational databases are a lot more time efficient and reduce errors that could
otherwise occur.
Using a relational database provides many benefits. One major benefit is the lack of data
redundancy. Since all tables will be linked through relationships, there won’t be any duplicate values
inputted. This reduces errors since having to type the same value many times could lead to inputting
it incorrectly. With relational databases only the original value is inputted and then linked to other
parts of the database. When this value is changed, it will change in all other parts of the database
where it is present. This is a major benefit since it saves time and reduces the chance of errors that
could occur. Data can also be easily extracted and displayed with the use of queries and reports. This
allows for the ease to look at data and see what exactly is happening.
Some key features of a relational database are entities, attributes and relationships. Entities are the
tables in the database. These contain the information about whatever is being recorded. Attributes
are the specific pieces of information that will be recorded. For example, if the entity holds
information about customers, then the attributes will be things like customer name, ID, address, etc.
There are many different data types that each attribute can have. Text is used to enter most standard
text and characters. Up to 255 can be entered but should be reduced in size to save space in the
database. Long text or memo is used for very large amounts of text. Up to 64,000 characters can be
entered which can take up a lot of storage space. Number is used for inputting numerical information
and Date/Time is used for date and time. Currency is used for currency values. These all take up a
little amount of storage each. Yes/No is for used for questions and stores the answer as 0 for no and
–1 for yes. OLE object is used for images or graphs and can use a lot of storage space. Hyperlinks can
also be entered with it data type and depending on the length could take up a lot of storage. Lookup
wizard isn't technically a data type and when chosen, starts up the wizard to help you set up a simple
or complex lookup. Depending on which type of lookup chosen, depends on how many values can be
looked up and stored. There are also validation rules that can be set on the fields. For example, in the
title field you can set it so only Mr, Mrs or Miss can be entered. You could also set it up so they can
pick these options from a drop down box. AutoNumber generates a unique value for each record in
the table. These are used with primary and foreign keys but can be used outside of these.
A primary key is a unique number for each record in the database. Each record in the primary key has
a different number so it can't have the same as any other one. If you link a primary key to another
table in the database using relationships, then it will be copied to that table as a foreign key. Using
these relationships then you don't have to input data again and it copies the entities for you.
Joel Page 2
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