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ARCH-3: Database Design, a Practical Guide

ARCH-3: Database Design, a Practical Guide. Click to add subtitle. Gus Bj örklund. Wizard, Progress Software Corporation. Ask questions as we go if I am not being clear. Warning: there is a mistake in these slides. Rules are made to be broken. To every rule, there is an exception!.

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ARCH-3: Database Design, a Practical Guide

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  1. ARCH-3: Database Design, a Practical Guide Click to add subtitle Gus Björklund Wizard, Progress Software Corporation

  2. Ask questions as we goif I am not being clear.Warning: there is a mistake in these slides. ARCH-3: Database Design A Practical Guide

  3. Rules are made to be broken To every rule, there is an exception! ARCH-3: Database Design A Practical Guide

  4. If you thought this talk was going to be about indexing … It isn’t. Nor is it about performance. ARCH-3: Database Design A Practical Guide

  5. Topics • Theory: • What is Database Design • Basic Elements • Representing the Model as Tables • Practice • An Example • Some Other Topics ARCH-3: Database Design A Practical Guide

  6. First, a little theory ARCH-3: Database Design A Practical Guide

  7. What do we mean by database design? • A process for defining a model of a subset of the “real”1 world, then representing it as data in tables in a relational databaseAt least, that’s the definition we will use for the purposes of this talk. 1 Well, for small values of real, anyway. ARCH-3: Database Design A Practical Guide

  8. Basic Elements What do we put in our model? • Just 3 Things: • Entities • Attributes • Relationships The “entity-relationship model” was described by Peter Chen in 1976. See http://bit.csc.lsu.edu/~chen/chen.html ARCH-3: Database Design A Practical Guide

  9. Basic Elements: Entities • Can be thought of as nouns • People • author, composer, performer, seller, buyer • Places • home, IP address, URL, destination, factory, store • Things • song, recording, instrument, car, invoice Is “telephone number” a place or a thing? ARCH-3: Database Design A Practical Guide

  10. Basic Elements: Attributes Entities have attributes • Can be thought of as adjectives (but only loosely): • Length • Color • Horsepower • Part number • Song Title • Publication Date • Size • Fabric • Owner Is “telephone number” a attribute or an entity? ARCH-3: Database Design A Practical Guide

  11. Basic Elements: Relationships Entities are connected by relationships • Can be thought of as verbs: • has a • owns • contains • supervises • performs • called • sold • purchased • proved Is “telephone number” a relationship? ARCH-3: Database Design A Practical Guide

  12. Relationships have attributes too In May, 1995, Andrew Wiles published a proof of Fermat’s Last Theorem ARCH-3: Database Design A Practical Guide

  13. Relationships have attributes too In May, 1995, Andrew Wiles published a proof of Fermat’s Last Theorem attribute entity relationship entity ARCH-3: Database Design A Practical Guide

  14. What goes in an entity • Identifying attributes • Must be able to uniquely identify the entity • Can have more than one way to id • Id can be composite • Descriptive attributes • the values you need to keep track of • generally should be simple, not complex ARCH-3: Database Design A Practical Guide

  15. What to include in your model • The things your application has to keep track of • Telephones, wires, switches • The actions your application or its users perform • Make calls, send telephone bills, collect payments • Some attributes of the things and actions • Originating number, date and time of call, duration, called number • Keep it simple • Be accurate • Keep it up to date ARCH-3: Database Design A Practical Guide

  16. What to include in your model • Consider the goals of the system • Everything you include should be there for a reason you can state • in no more than two sentences • Everything should have a clear name • if you can’t name it, it doesn’t belong • Talk to the stakeholders !!! ARCH-3: Database Design A Practical Guide

  17. What to leave out of your model • The real world has properties that don’t matter (to your application) • The real world has relationships that don’t matter • Things happen in the real world that don’t matter • Keep it simple • If you can’t say why you need it, leave it out ARCH-3: Database Design A Practical Guide

  18. Logical vs Physical Data Models • Logical entities often require multiple tables to represent them • Tables can be thought of as logical or physical • It depends on your point of view • There is also the physical storage database layout • storage areas • data extents • disks • etc. • We aren’t going to talk about the physical database layout • We will talk about tables ARCH-3: Database Design A Practical Guide

  19. Mapping Your Model to a Database Simply put, • Entities become tables • Identifiers become indexes • Attributes become columns • Data types: pick appropriate • Relationships become tables or foreign keys ARCH-3: Database Design A Practical Guide

  20. “In theory, there is no difference betweentheory and practice, but in practice there is.”Jan van de Snepscheut ARCH-3: Database Design A Practical Guide

  21. Now for some practice. ARCH-3: Database Design A Practical Guide

  22. An example • Music store • Buys compact disc recordings from distributors • Has inventory • Allows customers to search for what they want • Maybe in an in-store kiosk or on the web • Sells compact discs to customers ARCH-3: Database Design A Practical Guide

  23. What should we do first? ARCH-3: Database Design A Practical Guide

  24. Activities • We buy discs from a distributor • Orders are sent to a distributor • Orders are delivered to the store • Orders may be cancelled • We sell discs to customers in sales transactions • Customers buy discs in sales transactions • Customers search for what they want to buy Which of these must be remembered by the system? ARCH-3: Database Design A Practical Guide

  25. What do we need to keep track of • Discs we have • Discs we sold • Discs we know about and can get • Discs we have ordered • Information needed to do our income tax • what we paid for stock • when we bought it • what we sold it for • when we sold it ARCH-3: Database Design A Practical Guide

  26. Disc entities • UPC Code: 8697-07416-2 • Manufacturer: Sony BMG • Cost to us: $ 2.00 • Price charged: $ 17.95 • Tax charged: $ 0.80 • Date purchased: March 19, 2007 • Date sold: June 9, 2007 ARCH-3: Database Design A Practical Guide

  27. Disc table might look like this ARCH-3: Database Design A Practical Guide

  28. What’s wrong? • Is upc a unique identifier? • Might have bought from a distributor • Have no information about what is on the disc • How do customers search? • Don’t know when disc was made • Could be more than one tax jurisdiction • provincial tax, city tax • Don’t know if disc is on order • Don’t know who bought it • Duplicated data • Etc., etc. ARCH-3: Database Design A Practical Guide

  29. Disc entities take 2 • UPC Code: 8697-07416-2 • Manufacturer: Sony BMG • Distributor: Bob’s Wholesale CD’s • Cost to us: $ 2.00 • Price charged: $ 17.95 • Tax charged: $ 0.80 • Date ordered: March 19, 2007 • Date received: March 20, 2007 • Date sold: June 9, 2007 • Disc Title: “The Essential Joshua Bell” • Artist: Joshua Bell • Track 1: “Danse Russe” • Track 2: “Violin Concerto in E Minor” • Track 3: “Nocturne in C-sharp Minor” • etc. ARCH-3: Database Design A Practical Guide

  30. Example: Now What’s wrong? • This is getting messy • Activities combined with disc’s attributes • Have duplicated information • How many tracks can there be? • What if there is more than one artist? • Don’t have all the information a customer might want to use to search ARCH-3: Database Design A Practical Guide

  31. Discs revisited • Discs have titles • Discs have pictures on the cover • Discs contain tracks • Discs are made by manufacturers • Discs are purchased from distributors • Discs are ordered from distributors • Discs are delivered to the store • Discs are sold to customers ARCH-3: Database Design A Practical Guide

  32. “Discs contain tracks …” • Tracks contain songs • Tracks occur in order • Tracks have a duration • Songs are performed in performances • Songs have performers (usually) • Songs have composers • Songs have names (titles) • Songs have a key (but not always) • Performances are done by performers • Performers can be groups (bands, orchestras, etc.) • Performances are performed in a location or venue ARCH-3: Database Design A Practical Guide

  33. Discs Manufacturers Distributors Orders Customers Inventory Tracks Songs Performers Groups ? We seem to need these entities ARCH-3: Database Design A Practical Guide

  34. Songs have names (titles).Are names properties of songs?Or are they entities related to songs?Or are they something else? ARCH-3: Database Design A Practical Guide

  35. Song data (track 1) ARCH-3: Database Design A Practical Guide

  36. Song data (track 2) ARCH-3: Database Design A Practical Guide

  37. Performance data ARCH-3: Database Design A Practical Guide

  38. Performance data take 2 ARCH-3: Database Design A Practical Guide

  39. Performer data ARCH-3: Database Design A Practical Guide

  40. Performance to Performer Relationship ARCH-3: Database Design A Practical Guide

  41. Performance data take 3 ARCH-3: Database Design A Practical Guide

  42. Track to Performance Relationship ARCH-3: Database Design A Practical Guide

  43. Relationships (so far): track performance one to one performer performance performance disc performer track performance track one to many many to many track ARCH-3: Database Design A Practical Guide

  44. What happened to Songs? ARCH-3: Database Design A Practical Guide

  45. Relationships (take 2): song performance track song one to many performance one to one performance disc performer track performance track performance one to many performer track performance many to many ARCH-3: Database Design A Practical Guide

  46. disc track performance performer track track performance performer song song song performance Relationships (take 3): ARCH-3: Database Design A Practical Guide

  47. What about“business entities”?Where are they? ARCH-3: Database Design A Practical Guide

  48. disc track performance performer track track performance performer song song song performance Business entities ARCH-3: Database Design A Practical Guide

  49. disc track performance performer track track performance performer song song song performance Business entities ARCH-3: Database Design A Practical Guide

  50. disc track performance performer track track performance performer song song song performance Business entities ARCH-3: Database Design A Practical Guide

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