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Project and Data Management Software

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Presentation on theme: "Project and Data Management Software"— Presentation transcript:

1 Project and Data Management Software
Data Analysis and Data Modelling Normalisation Project and Data Management Software

2 Project and Data Management Software
Normalisation Normalisation provides an algorithm for reducing complex data structures into simple structures Formalised by set of rules known as Codd’s laws Tidying up the data so there is no data redundancy Ensuring data is grouped logically Project and Data Management Software

3 Project and Data Management Software
Why Use Normalization? Relations formed by the process makes the data easier to understand and manipulate. Provides a stable base for future database growth. Simplifies relations and reduces anomalies. Project and Data Management Software

4 Stages of Normalization
There are 3 stages: 1st Normal Form – 1NF 2nd Normal Form – 2NF 3rd Normal Form – 3NF BCNF Boyce Codd Normal Form 4NF also exists Project and Data Management Software

5 Project and Data Management Software
First Normal Form – 1NF For a relation to be in 1NF all its attributes must be atomic Each attribute must contain a single value not a repeating group of values. Every non-primary key attribute must be functionally dependent on the Primary Key. Project and Data Management Software

6 Project and Data Management Software
Un-normalised data Course Code Course Desc Employee Number Name Block Room No Date Joined Course Allocated Hours In line with recent policy all staff are released for two hours a week for staff dev. Employees work at their own pace in a lab. A total of six attributes are recorded about each employee including their normal office location (block and room), the date they joined the course and how many hours it is planned for them to work on it. Project and Data Management Software

7 Project and Data Management Software
Un-normalised data A list of fields needed for the system E.g. Staff Development Course All staff are released for two hours a week for staff dev. Employees work at their own pace in a lab. A total of six attributes are recorded about each employee including their normal office location (block and room), the date they joined the course and how many hours it is planned for them to work on it. In line with recent policy all staff are released for two hours a week for staff dev. Employees work at their own pace in a lab. A total of six attributes are recorded about each employee including their normal office location (block and room), the date they joined the course and how many hours it is planned for them to work on it. Project and Data Management Software

8 Project and Data Management Software
First Normal Form (1NF) An entity is in 1NF if, and only if, it has an identifying key and there are no repeating attributes or groups of attributes To get to 1NF we must remove all repeating groups (data elements) Project and Data Management Software

9 Project and Data Management Software
Our Example COURSE EMP_ON_COURSE Course Code Course Desc. Employee Number Name Block Room No Date Joined Course Allocated Hours Project and Data Management Software

10 Second Normal Form (2NF)
An entity is in 2NF if, and only if, it is in 1NF and has no attributes which require only part of the key to identify them uniquely To get to 2NF we remove part key dependencies All data items must be dependant on the primary key Project and Data Management Software

11 Project and Data Management Software
Our Example Course is already in 2NF Emp_On_Course is not because Attribute Depends On Name Block RoomNo Employee No Attribute Depends On Date Joined Hours Employee No + Course Code Project and Data Management Software

12 Project and Data Management Software
So we.. Take out details that are linked only to employee into a separate table If in any doubt, ask a question such as ‘Are these fields affected when they join a course’ Attribute Depends On Name Block RoomNo Employee No Project and Data Management Software

13 Project and Data Management Software
Cont. COURSE EMP_ON_ EMPLOYEE Course Code Course Desc Emp No Date Joined Course Allocated Hours Name Block Room No Project and Data Management Software

14 Project and Data Management Software
Problems Block and Room Number are related, so if one is updated the other will be affected. If the block names change, then the whole of the employee records will have to be altered Project and Data Management Software

15 Project and Data Management Software
Third Normal Form (3NF) An entity is in 3NF if, and only if, it is in 2NF and no non-key attribute depends on another non-key attribute. To get to 3NF we must remove attributes that depend on other non-key attributes It removes any mutual dependence between non-key attributes Project and Data Management Software

16 Project and Data Management Software
Third Normal Form 3NF In other words: “The attributes is a relation in 3NF must depend on the key, the whole key and nothing but the key” ! Project and Data Management Software

17 How to do that: Dependency
Decide on the direction of the dependency between the attributes If B determines A, then A is dependant on B If A depends on B, create a new entity, keyed by B, with A as an attribute Leave B in the original entity and mark it as a foreign key, but remove A from the original entity Project and Data Management Software

18 Our Example: Dependency
If, given a value for A, there is only one possible value for B, then B is dependant on A Therefore, given a value for room no., there is only one value for block. The same is not true vice-versa. Hence Block is dependent on Room No. Leave Room No in the original entity and mark it as a foreign key, but remove Block from the original entity Project and Data Management Software

19 Project and Data Management Software
Our Example Hence the EMPLOYEE (2NF) entity becomes EMPLOYEE LOCATION Employee No Name Room No * Room No Block * Room No is a foreign key in the Employee entity Project and Data Management Software

20 Entity Relationship Modelling
Course Location Emp_On_Course Employee Project and Data Management Software

21 Project and Data Management Software
Background - Keys Primary key Unique Identifier Can be made up of more than one attribute and then is called a composite key If there is no obvious choice, use a number Foreign Key Does not belong to the entity Used to relate entity to entity A primary key in another table Project and Data Management Software

22 Project and Data Management Software
To Normalise Follow 3 simple steps Remove all repeating data elements Ensures data items are dependant on the primary key Remove all fields dependant on non-key fields Project and Data Management Software


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