Database DesignPowerPoint PresentationSlide 3What Is Entity-Relationship Diagrams?Slide 5Slide 6Entity-Relationship DiagramsBusiness Rules (1)Business Rules (2)Business Rules (3)Business Rules (4)Business Rules (5)Business Rules (6)Business Rules (7)Business Rules (8)E-R Diagrams (1)Entity Relationship DiagramsDeveloping ERDsSlide 19How do we start an ERD? (1)How do we start an ERD? (2)How do we start an ERD? (3)ERDsCrucial Use of E-R Analysis (1)Crucial Use of E-R Analysis (2)Crucial Use of E-R Analysis (3)Discussion QuestionsTasks for Next Lecture2003SJSU -- CmpE L4-S1 ER DiagramsDatabase Design Dr. M.E. Fayad, ProfessorComputer Engineering Department, Room #283I College of EngineeringSan José State UniversityOne Washington SquareSan José, CA 95192-0180 http://www.engr.sjsu.edu/~fayad2003SJSU – CmpE --- M.E. Fayad L4-S2 ER Diagrams2Lesson 4:Entity Relationship Diagrams (ERD)2003SJSU – CmpE --- M.E. Fayad L4-S3 ER Diagrams Lesson ObjectivesObjectives3 Understand the notation of ERDs Learn how to do ER Analysis Illustrate examples for ERDs2003SJSU – CmpE --- M.E. Fayad L4-S4 ER DiagramsE-R diagrams (ERDs):–Identify major ingredients, entities, of a complicated situation–Identify characteristics, attributes, of the major ingredients–Uncover and analyze interconnections, relationships, among the major ingredients–Assess various aspects of the relationships4What Is Entity-Relationship Diagrams?2003SJSU – CmpE --- M.E. Fayad L4-S5 ER DiagramsERD – Chen 1976Precursor to the class diagram – Will be covered later.No generalizationERD–Entities: Information holding structures–Relationships: Connections between entities–Cardinalities: Upper bounds–Modalities: Lower bounds–Attributes: Properties, characteristics, … associated with an entity.5What Is Entity-Relationship Diagrams?2003SJSU – CmpE --- M.E. Fayad L4-S6 ER DiagramsIn short, ERD strives– to take a close look at the ingredients of a puzzle–in order to identify major and minor ingredients–and to figure out how they relate to each other6What Is Entity-Relationship Diagrams?2003SJSU – CmpE --- M.E. Fayad L4-S7 ER DiagramsERD can be summarized as the process of uncovering, analyzing, and explicating (i.e., stating clearly and fully) the business rules governing a complicated situation7Entity-Relationship Diagrams2003SJSU – CmpE --- M.E. Fayad L4-S8 ER DiagramsBusiness rules are precise statements, derived from a detailed description of the organization's operations, that define one or more of the following modeling components:–Entities–Relationships–Attributes–Connectivities–Cardinalities–Constraints1Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM8Business Rules (1)2003SJSU – CmpE --- M.E. Fayad L4-S9 ER DiagramsExamples of business rules1–An invoice contains one or more invoice lines, but each invoice line is associated with a single invoice. That is,•An invoice contains one or more invoice lines.•Each invoice line is associated with a single invoice.–A store employs many employees, but each employee is employed by only one store.–A college has many departments, but each department belongs to a single college. (This business rule reflects a university that has multiple colleges such as Business, Liberal Arts, Education, Engineering, etc.)1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM9Business Rules (2)2003SJSU – CmpE --- M.E. Fayad L4-S10 ER DiagramsExamples of business rules1 –A driver may be assigned to drive many different vehicles, and each vehicle can be driven by many drivers. (Note: Keep in mind that this business rule reflects the assignment of drivers over a period of time.)–A client may sign many contracts, but each contract is signed by only one client.–A sales representative may write many contracts, but each contract is written by one sales representative 10Business Rules (3)2003SJSU – CmpE --- M.E. Fayad L4-S11 ER DiagramsSome business rules for a library–Books and other materials exist in various editions and numbers of copies–Books may or may not circulate–Books that circulate may do so for varying periods•Periods may be determined by –Book status alone–Borrower status alone–Combination of book status and borrower status11Business Rules (4)2003SJSU – CmpE --- M.E. Fayad L4-S12 ER DiagramsMore business rules for a library•Users may have various statuses•Users may have varying numbers of items currently charged out to them•Users may or may not owe fines–Fine status may or may not affect eligibility to borrow12Business Rules (5)2003SJSU – CmpE --- M.E. Fayad L4-S13 ER DiagramsMore business rules for a library•Staff members have attributes of–Salary or wage rates–Annual leave–Sick leave–Work schedules–Job titles–Special skills (e.g., languages, puppetry)–Hire dates–Total length of service–Professional organization memberships13Business Rules (6)2003SJSU – CmpE --- M.E. Fayad L4-S14 ER DiagramsMore business rules for a library•Physical facilities include–Branches–Furniture–Machines (e.g., computers, microform readers, automobiles, players for CD-ROMs, audiotapes, videotapes)–Library-management software–Catalog records (e.g., computerized databases, catalog cards)–Records of inventory, acquisitions, circulation, personnel14Business Rules (7)2003SJSU – CmpE --- M.E. Fayad L4-S15 ER DiagramsMore business rules for a library•Related organizations may include–City, university, or corporate administrations–Employee unions–Friends of the Library organizations–Vendors of books, serials, and other products and services used by the library–Networks of which the library is a member (e.g., OCLC, Amigos, Association of Research Libraries, Texas State Library network, Central Texas Library System)15Business Rules (8)2003SJSU – CmpE --- M.E. Fayad L4-S16 ER DiagramsE-R analysis relies heavily on diagrams to represent–Entities (rectangles)–Attributes (ellipses)–Relationships (diamonds)–Connections (lines, which may have arrowheads or
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