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The Relational Database Model & The Database Development Process

Fact of the Week: According to a Gartner study in ‘06, Microsoft SQL server had the highest annual growth of any proprietary DBMS at 28% increasing market share from 15.6% to 17.4%. The Relational Database Model & The Database Development Process. Learning Objectives.

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The Relational Database Model & The Database Development Process

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  1. Fact of the Week: According to a Gartner study in ‘06, Microsoft SQL server had the highest annual growth of any proprietary DBMS at 28% increasing market share from 15.6% to 17.4% The Relational Database Model & The Database Development Process

  2. Learning Objectives • Describe the Relational Model • Define relational terms and understand the terminology in practice. • Understand these relational terms through practice • Explain the System Development Life Cycle (SDLC) • Explain the Database Life Cycle (DBLC)

  3. Fundamental Axioms of DBMSs • Users communicate with computer applications (websites, etc) • Computer applications communicate with DBMSs. • Users do not communicate with DBMSs directly. • As a result DBMSs although they can be used interactively, are not used interactively. • A DBMS is not a replacement for sound database design principles.

  4. First of many examples for the semester • https://labjobs.ischool.syr.edu Website Db using Relational Model You Web Server (IIS) Web Browser SQL Server User Interface and Business Logic (HTML/C#) Data access logic and Data (SQL) ApplicationComponents

  5. The Relational Database Model • Many DBMS applications implement the Relational Model, but none of them enforce it. This permits rookie database designers to shoot themselves in the foot. And many have (including yours truly). • The Relational Model has: (Codd’s 3 rules) • 1)Data Independence • Clear separation between data and metadata • 2) Data Consistency • Minimal redundancy; the data adopts the “DRY” principle • 3) Easy to use • You don’t have to understand the implementation to use it.

  6. You can build a poorly-designed DB in a DBMS Do you see problems with this database design?Think Codd: Independence? Consistency? Ease-of-Use? Change Sally Jones’s phone #? How many ‘Software’ in the database? Add New Employee Bob Smith? Delete Dave Smith (no longer works here)

  7. Activity: Relational Terminology Identify Each of These : • Table • Relation • Row • Column • Tuple • Attribute • Physical Domain • Logical Domain

  8. Tables are “Buckets for yer data” “Products Appear on Orders” “Customers Place Orders” Orders • Tables: • Specialized • Order doesn’t matter • Contain real items Customers Products

  9. DBMS : Physical Domain Different “flavors” of DBMSs use different data types.

  10. DBMS: Logical Domain / Constraints • Default Value – a value entered into an attribute for a row when one isn’t specified. • Check Constraint – an expression which must be evaluated prior to the insertion of a row. Eg. Employee_hourly_wage >= 0 • Unique Constraint – ensures duplicate values are not inserted into a column. (Secondary Keys should have unique constraints) • Lookup table – a separate table containing all of the acceptable values for a given column, typically varchar (Think drop down list) The column you’re trying to constrain is a FK to the lookup table.

  11. Activity: The Relational Table Relation Name? Attributes? Physical Domain of Columns? Logical Domain of Columns? Candidate Keys?

  12. The Primary Key Constraint • Special selectedconstraint (you choose it) • Enforces entity integrity on the table. • Must be data unique for each row • Should be a candidate key

  13. Good PK / Bad PK Good candidate key choices? • Customer Name? • Email Address? • Name and DOB? • SSN? • Customer Selected value? • Random Unique #? • Sequential Unique #? • Last two are examples of surrogate keys • The best PK’s • Don’t change … ever! • Have no external meaning ... • Do not compromise security… • Do not hinder performance …

  14. Activity: Which of these is a good PK? Candidate keys? Best primary key? Why? Should a Surrogate key be used?

  15. The Foreign Key constraint • The foreign key is a column added to one relation so that it can be associated with another relation. • Foreign keys must have referential integrity – their values must come from the corresponding PK column in the relation.

  16. Example of FK: The Lookup Table Foreign Key

  17. Activity: Find the keys • Candidate? Primary? Foreign? Secondary? Surrogate?

  18. One more time. Tables Rule for joining tables Columns:Physical Domain? Logical Domain? Alllow Null? Keys: Candidate? Primary? Foreign, Surrogate, Secondary?

  19. The Natural Join of PK-FK at Work NaturalJoin

  20. FK Example: Implementation of a 1-M Relationship

  21. FK Example: Implementation of a M-N Relationship This M-M Relationship has been resolved into two 1-M relationships

  22. Example:Null and Flags Nulls typically cause problems in Varchar andNumeric, and bit fields 103 and 105 are null for different reasons! Null makes sense for this column Flags used to represent different status

  23. Data Models: Abstraction Levels Conceptual Highly AbstractHardware and Software Independent Logical Somewhat Abstract Hardware Independent Software Dependent Internal External Not Abstract (Concrete)Hardware and Software Dependent Physical

  24. SDLC / DBLC IPlanning IIAnalysis IIIDesign IVImplementation VMaintenance &Support Resources LogicalModel Conceptual Model PhysicalModel Internal / ExternalModel Time Systems Development Lifecycle

  25. The Relational Database Model & The Database Development Process Questions?

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