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Project and Data Management Software

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

  2. 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. 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. 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. Un-normalised data Project and Data Management Software

  7. 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 towork on it. Project and Data Management Software

  8. 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. Our Example 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. Our Example • Course is already in 2NF • Emp_On_Course is not because Project and Data Management Software

  12. 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’ Project and Data Management Software

  13. Cont. Project and Data Management Software

  14. 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. 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. 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. Our Example • Hence the EMPLOYEE (2NF) entity becomes * 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. 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. 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