1
Information Management Centre, Thames Valley University
Relational Modelling
(Normalisation)
Abdisalam Issa-Salwe
Facult...
2
Information Management Centre, Thames Valley University
UNF – 1NF
Applicant
Applicant Number
Applicant Name
Applicant Ad...
3
Information Management Centre, Thames Valley University
UNF: Remove Repeating Groups
 Create a new group for the multi-...
4
Information Management Centre, Thames Valley University
Company Name
Company Number
Job TitleCompany Name
Job Ref Number...
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Information Management Centre, Thames Valley University
Applicant
Applicant's Job
Applicant Number
Applicant Name
Applic...
6
Information Management Centre, Thames Valley University
1NF – 2NF
Applicant Number
Applicant Name
Applicant Address
*App...
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Information Management Centre, Thames Valley University
Partial Dependency example
 Job
Reference
Number
determines
Job...
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Information Management Centre, Thames Valley University
2NF
Company Name
Company Number
Job Title
Job Ref Number
*Applic...
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Information Management Centre, Thames Valley University
 Remove the data items that depend on
the non-candidate key att...
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Information Management Centre, Thames Valley University
2NF – 3NF
2NF 3NF
Job Reference Number Job Reference Number
Job...
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Information Management Centre, Thames Valley University
2NF – 3NF
Applicant
Applicant's Job
Job
Job Ref Number
Title
Co...
12
Information Management Centre, Thames Valley University
Functional Dependency
 A Function in mathematics is a relation...
13
Information Management Centre, Thames Valley University
Unnormalised Entity
Begin with an entity from
the logical data ...
14
Information Management Centre, Thames Valley University
Second Normal Form (2NF)
If an entity has a concatenated identi...
15
Information Management Centre, Thames Valley University
Potential anomalies
 UPDATE the price per session of facility ...
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Week 7 normalisation lecture (last)

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Week 7 normalisation lecture (last)

  1. 1. 1 Information Management Centre, Thames Valley University Relational Modelling (Normalisation) Abdisalam Issa-Salwe Faculty of Professional Studies Thames Valley University Week 7 Seminar Information Management Centre, Thames Valley University Company Name Company Number Job Title Job Ref Number Applicant Address Applicant Name Applicant Number 1NFUNF
  2. 2. 2 Information Management Centre, Thames Valley University UNF – 1NF Applicant Applicant Number Applicant Name Applicant Address Job Ref Number Job Title Company Number Company Name Information Management Centre, Thames Valley University Company Name Company Number Job Title Job Ref Number Applicant Address Applicant Name Applicant Number 1NFUNF
  3. 3. 3 Information Management Centre, Thames Valley University UNF: Remove Repeating Groups  Create a new group for the multi-valued attributes  Include the Primary Key attribute from the original group as a Foreign Key in the new group  Choose a key for the new group Information Management Centre, Thames Valley University Company Name Company Number Job TitleCompany Name Job Ref NumberCompany Number Job Title Job Ref Number Applicant AddressApplicant Address Applicant NameApplicant Name Applicant NumberApplicant Number 1NFUNF
  4. 4. 4 Information Management Centre, Thames Valley University Company Name Company Number Job TitleCompany Name Job Ref NumberCompany Number *Applicant NumberJob Title Job Ref Number Applicant AddressApplicant Address Applicant NameApplicant Name Applicant NumberApplicant Number 1NFUNF Information Management Centre, Thames Valley University Applicant Applicant's Job Applicant Number Applicant Name Applicant Address Job Ref Number Job Title Company Number Company Name
  5. 5. 5 Information Management Centre, Thames Valley University Applicant Applicant's Job Applicant Number Applicant Name Applicant Address Job Ref Number Job Title Company Number Company Name *Applicant Number 1NF – 2NF Information Management Centre, Thames Valley University 1NF – 2NF Applicant Number Applicant Name Applicant Address *Applicant Number *Job Ref Number Applicant Applicant's Job Job Job Reference Number Job Title Company Number Company Name
  6. 6. 6 Information Management Centre, Thames Valley University 1NF – 2NF Applicant Number Applicant Name Applicant Address *Applicant Number *Job Ref Number Applicant Applicant's Job Job Job Reference Number Job Title Company Number Company Name Information Management Centre, Thames Valley University 1NF to 2NF: Remove Partial Dependencies  Partial dependency only arises where we have a compound key  It describes the situation where there is a functional dependency between one part of the key and some non-key attribute  e.g. Job Reference Number determines Job Title, Company Number and Company Name
  7. 7. 7 Information Management Centre, Thames Valley University Partial Dependency example  Job Reference Number determines Job Title Job Ref Number Applicant Number Job Title J24 A1001 Trainee SA J24 A1002 Trainee SA J99 A1002 IT Manager Information Management Centre, Thames Valley University 1NF to 2NF: Remove Partial Dependencies (cont…)  Create a new group for all the partially dependent data items  The Primary Key of the new group will be the attribute(s) that the partially dependent data items depended on  The key of the original group does not change
  8. 8. 8 Information Management Centre, Thames Valley University 2NF Company Name Company Number Job Title Job Ref Number *Applicant Number 1NF Information Management Centre, Thames Valley University 2NF to 3NF: Remove Transitive Dependencies  A transitive dependency arises where there is a dependency between two data items neither of which is a candidate key for the data group in question  e.g. Company Number determines Company Name
  9. 9. 9 Information Management Centre, Thames Valley University  Remove the data items that depend on the non-candidate key attribute  The attribute that determines them is the Primary Key of the new group  Leave behind a copy of this attribute as a Foreign Key 2NF to 3NF: Remove Transitive Dependencies (cont…) Information Management Centre, Thames Valley University 2NF – 3NF Company Name Company Number Company Name Company Number Job TitleJob Title Job Reference NumberJob Reference Number 3NF2NF
  10. 10. 10 Information Management Centre, Thames Valley University 2NF – 3NF 2NF 3NF Job Reference Number Job Reference Number Job Title Job Title Company Number Company Name Company Number Company Name Information Management Centre, Thames Valley University 2NF – 3NF 2NF 3NF Job Reference Number Job Reference Number Job Title Job Title Company Number *Company Number Company Name Company Number Company Name
  11. 11. 11 Information Management Centre, Thames Valley University 2NF – 3NF Applicant Applicant's Job Job Job Ref Number Title Company Number Company Name Information Management Centre, Thames Valley University 2NF – 3NF Applicant Applicant's Job Job Company Company Number Company Name Job Ref Number Title *Company Number
  12. 12. 12 Information Management Centre, Thames Valley University Functional Dependency  A Function in mathematics is a relation between two domains A,B such that  for every a in A there is exactly one corresponding b in B  e.g. A and B both real numbers:  square(x) is a function  but  sqrt(x) is not a function  sqrt(4) = (-2,2) since -2*-2 = 4 as well as 2*2=4  this is an example of a non-functional dependency Information Management Centre, Thames Valley University Mnemonic  “the key, the whole key and nothing but the key”  2NF  “the key” : non-key fields depend on the key  “the whole key”: non-key fields depend fully on the key  3NF  “nothing but the key”: non-key fields are not dependent on each other
  13. 13. 13 Information Management Centre, Thames Valley University Unnormalised Entity Begin with an entity from the logical data model Information Management Centre, Thames Valley University First Normal Form (1NF) Look for repeating groups of attributes and remove them into separate entities
  14. 14. 14 Information Management Centre, Thames Valley University Second Normal Form (2NF) If an entity has a concatenated identifier, look for attributes that depend only on part of the identifier. If found, remove to new entity. Information Management Centre, Thames Valley University Third Normal Form (3NF) Look for attributes that depend only on another non-identifying attribute. If found, remove to new entity. Also remove any calculated attributes.
  15. 15. 15 Information Management Centre, Thames Valley University Potential anomalies  UPDATE the price per session of facility 1  now different rates for squash courts - suspect business rule is same rate for all facilities for a ‘sport’  ADD a new tennis court  must also ensure the same rate is used as for other tennis courts  DELETE facility 11  lose the rate per session for skittles Information Management Centre, Thames Valley University Summary: Data modelling  Data modelling answers the question:  What data exists and what is the most efficient way of organising it?  Data Modelling is the analysis of data in organisations, departments, branches, etc.  It captures all the data uses,  It organises it into an efficient structure.  Data modelling = the construction of a model of the data requirements of the organisation.  Data requirements are more stable that processing requirements.  There are two techniques:  1. Entity-relationship modelling - a top down approach. 2. Normalisation - a bottom up approach.

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