1 / 13

Chapter 5

Chapter 5. Normalization of Database Tables Example Database Systems: Design, Implementation, and Management, Rob and Coronel Special adaptation for INFS-3200. Database Tables and Normalization. Original Data. Data in 1NF. Dependency Diagram (1NF).

ovidio
Download Presentation

Chapter 5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 5 Normalization of Database Tables Example Database Systems: Design, Implementation, and Management, Rob and Coronel Special adaptation for INFS-3200

  2. Database Tables and Normalization Original Data Database Systems: Design, Implementation, & Management, Rob & Coronel

  3. Data in 1NF Database Systems: Design, Implementation, & Management, Rob & Coronel

  4. Dependency Diagram (1NF) 1NF (PROJ_NUM, EMP_NUM, PROJ_NUM,EMP_NAME, JOB_CLASS, CHG_HOUR, HOURS) Partial Dependencies: (PROJ_NUM -> PROJ_NAME) (EMP_NUM -> EMP_NAME, JOB_CLASS, CHG_HOUR) Transitive Dependencies: (JOB_CLASS -> CHG_HOUR) Database Systems: Design, Implementation, & Management, Rob & Coronel

  5. 2NF Conversion 1NF 2NF Table name: PROJECT PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME JOB_CLASS CHG_HOUR Table name: EMPLOYEE Transitive dependency PROJ_NUM EMP_NUM ASSIGN_HOURS PROJECT (PROJ_NUM, PROJ_NAME) EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS, CHG_HOUR) ASSIGN (PROJ_NUM, EMP_NUM, ASSIGN_HOURS) Transitive Dependencies: (JOB_CLASS -> CHG_HOUR) Table name: ASSIGN Database Systems: Design, Implementation, & Management, Rob & Coronel

  6. 3NF Conversion Table name: PROJECT JOB_CLASS EMP_NUM EMP_NAME JOB_CLASS JOB_CLASS CHG_HOUR CHG_HOUR Table name: EMPLOYEE Table name: JOB PROJ_NUM PROJ_NAME Transitive dependency Table name: ASSIGN PROJ_NUM EMP_NUM ASSIGN_HOURS PROJECT (PROJ_NUM, PROJ_NAME) EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS) JOB (JOB_CLASS, CHG_HOUR) ASSIGN (PROJ_NUM, EMP_NUM, ASSIGN_HOURS) Database Systems: Design, Implementation, & Management, Rob & Coronel

  7. Improving the Design • Evaluate PK Assignment (meet PK guidelines) • Evaluate Naming Conventions • Refine Attribute Atomicity (simple, single-valued) • Identify New Attributes • Identify New Relationships (decompose M:M) • Refine Primary Keys (as required for data granularity) • Maintain Historical Transactional Accuracy • Identify Use of Derived Attributes Database Systems: Design, Implementation, & Management, Rob & Coronel

  8. Evaluate PK Assignment Introduce a better suited PK free of semantic content (non-intelligent PK) Add JOB_CODE as surrogate PK. To reduce data entry errors Repeat for other tables (see # 6 – Assign)* Evaluate Naming Conventions JOB_CLASS is actually a description of the job, change to JOB_DESCRIPTION. CHG_HOURS should be JOB_CHG_HOUR Improving the Design(Job Table) Database Systems: Design, Implementation, & Management, Rob & Coronel

  9. Refine Attribute Atomicity Decompose composite attributes into simple attributes EMP_NAME should be EMP_LNAME EMP_FNAME EMP_INITIAL Identify New Attributes Add new attributes that describe real world entity characteristics EMP_HIREDATE Improving the Design(Employee Table) Database Systems: Design, Implementation, & Management, Rob & Coronel

  10. Improving the Design(Project Table) • Identify New Relationships • Add new relationships as required by business rules. • A project is managed by an employee, an employee can be the manager of only one project. • Add EMP_NUM as FK in PROJECT Database Systems: Design, Implementation, & Management, Rob & Coronel

  11. Improving the Design(Assign Table) • Identify new attributes • Add ASSIGN_DATE • Refine Primary Keys • Consider the “granulity” of the data being represented in order to determine the PK. • Can an employee have multiple hours worked entries for a given day in a given project? • If yes, add ASSIGN_NUM as surrogate PK. • Maintain Historical Transaction Accuracy • Add ASSIGN_CHG_HOUR • Identify Use of Derived Attributes • Add ASSIGN_CHARGE Database Systems: Design, Implementation, & Management, Rob & Coronel

  12. Final Normalized Design Database Systems: Design, Implementation, & Management, Rob & Coronel

  13. Limitations of System Assigned PK • Surrogate PK ensures that each row has an unique ID, not that the row’s dependent values are unique. • JOB_CODE system assigned PK • We still could have duplicate values: • 511 Programmer 35.75 • 512 Programmer 35.75 • Clearly, entries are duplicated! • To ensure unique values we must have create an unique index on all candidate keys. • Unique index on JOB_DESCRIPTION • This still will still not avoid data entry errors! • 513 Progranmer 35.75 Database Systems: Design, Implementation, & Management, Rob & Coronel

More Related