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DB design

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Database design

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DB design

  1. 1. 1 Database Requirements and Design
  2. 2. 2 DATA PEOPLE PROCEDURES HARDWARE SOFTWARE The Product: a working system
  3. 3. 3 Database development activities during the systems development life cycle (SDLC) Project Identification and Selection Project Initiation and Planning Analysis Physical Design Implementation Maintenance Logical Design
  4. 4. 4 Project Identification & Selection Purpose: to develop a preliminary understanding of the business situation that has caused the request for a new or enhanced information system. Deliverable: a formal request for services
  5. 5. 5 Project Identification and Selection  Printing Company: use internet to request quotes, place orders and check order status  Video Game Store: track customer information, track customer purchases, maintain inventory  Elementary school After School program: student records, important information, account balances  Interpreter’s Organizer: assignment status, income, costs, taxes
  6. 6. 6 Project Identification and Selection  Groups of 3-5, talk to me if you are thinking about an individual assignment  I would advise you use either a devise a case study with your group where you implement a database, or use a company/scenario that someone in your group is familiar with. Make sure everyone in the group understands the scenario  The next step in your group process should be to sit down and talk about the System Requirement. Make sure everyone in your group understands what data you want to get from the database.
  7. 7. 7 Project Initiation and Planning System Requirements:  Information requirements of the system  Stakeholders  Constraints  Application environment
  8. 8. 8 Case Study The Clearwater Traders Sales Order Database
  9. 9. 9 Overview Markets a line of clothing and sporting goods via mail-order catalogs To remain competitive, company managers want to create a database to allow Internet customers to: • Browse the catalog on-line • Place orders • Check order status status
  10. 10. 10 Information Requirements System must do all of the following: • Track information about customers and customer orders • Track customer orders • Track inventory information so customers can find out if an item is available • Have intranet applications, so Clearwater Traders personnel can: • Add, update, and delete inventory items • Update inventory amounts when new shipments are received • Modify item prices
  11. 11. 11 Stakeholders Company management Clearwater Traders personnel Customers
  12. 12. 12 Constraints System must be operational by April 2001 System must not require additional purchase of software/hardware Other possible constraints? Training employees, …
  13. 13. 13 Application Environment Access 2000 on networked PCs Expansion to Web sites using Visual Basic and Personal Web Server
  14. 14. 14 Logical Design Purpose: to elicit and structure all information requirements Deliverables: detailed functional specs for data, forms, reports, displays, and rules (logic, algorithms)
  15. 15. 15 Principles of Conceptual Database Design  Identify basic data needs and create conceptual data models that record needed data elements and their relationships  Your local Bank:  How many checking accounts do we have?  How many savings accounts?  How many customers?  How do we get each customer the right monthly statement?  How do I get a weekly report of overdue loan payments?
  16. 16. 16 Reality and Requirements Definition  Requires identifying user information requirements and representing them in a well-defined model  Model – a representation of reality that retains only selected details  Database Management System (DBMS) manages the database so that each user can record, access, and manipulate the data that is the “model of reality” of interest to the user  Requires mapping – associating elements in one sphere with elements in another sphere
  17. 17. 17 Conceptual Data Models  Object-oriented model  Represents real-world entities as objects rather than as records • Have their own object identities and attributes • Participate in relationships  Describes ways of manipulating data that focuses on the data and the manipulation (query, computation, update, etc.)
  18. 18. 18 Fundamentals  Objects  Important to users in the portion of reality modeled • Concrete objects • People, automobiles, trees, dishwashers, houses, hammers, books, etc. • Conceptual objects • Companies, skills, organizations, product designs, business transactions, job classifications, etc.
  19. 19. 19 Entity Relationship Diagram An entity-relationship diagram is a data modeling technique that creates a graphical representation of the entities, and the relationships between entities, within an information system.
  20. 20. 20 The three main components of an ERD are:  The entity is a person, object, place or event for which data is collected  The relationship is the interaction between the entities  The cardinality defines the relationship between the entities in terms of numbers.
  21. 21. 21 The steps involved in creating an ERD are:  Identify the entities;  Determine all significant interactions;  Analyze the nature of the interactions;  Draw the ERD
  22. 22. 22 Synonyms you should know… Entity = class = relation = table Attribute = column Instance = row rows columns table
  23. 23. 23 Relationships  MARRIED-MAN IS-MARRIED-TO MARRIED-WOMAN  MARRIED-MAN = {Adam, David, John} and  MARRIED-WOMAN = {Joan, Linda, Michelle} and  Adam is-married-to Joan  David is-married-to Linda  John is-married-to Michelle  IS-MARRIED-TO =  { (Adam, Joan), (David, Linda), (John, Michelle) }
  24. 24. 24 Representations of a Relationship Married Man Married Woman IS MARRIED TO (a) The IS MARRIED TO relationship Adam ----------------------------------- Joan David ----------------------------------- Linda John ----------------------------------- Michelle (b) Some instances of IS MARRIED TO
  25. 25. 25 Cardinality  Refers to the maximum number of instances of 1 object set related to a single instance of the other object set Married Man Married Woman IS MARRIED TO 1 1 Supervisor WorkerSupervises1 * 1:1 relationship 1:M or 1:* relationship
  26. 26. 26 Basic E-R Notation
  27. 27. 27 Sample E-R Diagram
  28. 28. 28 E-R model with only the necessary entities
  29. 29. 29 Primary key attribute
  30. 30. 30 Composite key attribute
  31. 31. 31 Relationship types and instances (a) Relationship type “Completes”
  32. 32. 32 Cardinality constraints (a) Relationship showing maximum cardinality only.
  33. 33. 33 (b) Relationship showing max & min cardinality Cardinality constraints
  34. 34. 34 Building a Conceptual Data Model from a Purchase Order PAYMENT Check # Date ORDER Number Tax TotalDate VENDOR Number Name Address * INCLUDES * 1 MADE FROM * 1 PAID WITH 1 PRODUCT Stock # Description Price
  35. 35. 35 Representing Tables (entities)  Vendor (Number, Name, Address)  Product (Stock #, Description, Price)  Order (Number, Date, Tax, Total)  Payment (Check #, Date) Attributes are in parentheses Primary key is underlined.
  36. 36. 36 Physical Design Purpose: to develop all technology & organizational specs Deliverables: program & database structures, technology purchases, physical site plans and organizational redesigns
  37. 37. 37 Implementation Purpose: to write programs, build data files, test and install the new system, train users, and finalize documentation Deliverables: programs that work accurately and to specs, documentation (user and system), and training materials.
  38. 38. 38 For Practice... Identify a potential key value for each of the following entities: • Customer (Cust-Name, Cust-ID, Address, Country, Balance, Month-to-date-payments) • Sales Rep (Comm%, Office, Manager-ID, Sales Rep Name, Sales Rep ID) • Product (Prod-Desc, Mfg-ID, Cost, Price, Prod-ID)
  39. 39. 39 For Practice... For each of the following, draw a data model showing a relationship between objects and attributes of the objects. Indicate cardinality. • Students take classes and get grades in the classes. • Sections of courses are offered at specified times and in specified rooms of buildings. • Employees work a certain number of hours and have a certain supervisor. • People subscribe to magazines, and their subscriptions have beginning and ending dates.

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