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Entity-Relationship Model SE 157A, Fall Semester 2006 Robert Correll.

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Presentation on theme: "Entity-Relationship Model SE 157A, Fall Semester 2006 Robert Correll."— Presentation transcript:

1 Entity-Relationship Model SE 157A, Fall Semester 2006 Robert Correll

2 Entity-Relationship Model (chapter 6) Basic Concepts Constraints, Keys, and Design Issues Entity-Relationship Diagram Extended E-R Features Design of an E-R Database Schema Reduction of an E-R Schema to Tables Unified Modeling Language (UML)

3 Basic Concepts Logical structure of database system Requires iterative and incremental process o Requirements, analysis, design, … o “Inception, elaboration, construction, …” 1 Overall objective: o Minimize redundancy (space and updates) o Maximize effectiveness (the right product)

4 Constraints, Keys, and Design Issues Job Search Activity System: o A thorough record of events o Helps in demonstrating competency o Activity example: received automated reply o Requirements specification

5 Requirements Specification Track activities associated with job search: o List companies or locations of a company o List contacts per location or per job o List jobs per zip code or per contact o List activity per contact, company, or job o List follow-up dates per contact o List referrals (recursive relationship)

6 Entity-Relationship Diagram Identify entity sets Determine attributes Analyze interactions between entities Draw the E-R Diagram Remember iterative and incremental process.

7 Identify Entity Sets One job seeker Activity Company Location Job Contact Pending follow-up date

8 Determine Attributes location_id street location city zip_code state company_idco_name company stock_symbol web_site last_search_date Shows a derived attribute: last_search_date.

9 Determine Attributes (continued) Shows composite attribute name, which includes the attributes prefix, first_name, and last_name. first_name contact_idname contact rapor_level telephone title last_name prefix last_activity_date my_job_idco_job_id job position_type source position job_status

10 Determine Attributes (continued) activity_dateactivity_time activity comment activity_code description activity_description Each description represents a specific job search activity. contact_idfollow-up_date follow-up job_seeker

11 Activity Description Codes 1Conducted search but did not apply 2Applied on company website 3 ed resume 4Sent resume via regular mail 5Received automated reply 6Received personalized 7Received voice mail message 8Received call and spoke over phone 9Left contact voice mail message 10Called contact and spoke over phone 11Had on-site interview

12 Analyze Interactions company_idco_name company stock_symbol web_site last_search_date location_id street location city zip_code state company_location Weak entity set with discriminator

13 Extended E-R Features Specialization: superclass-subclass (ISA) Generalization: entity sets share attributes Attribute inheritance: higher- and lower-level Aggregation: back-to-back relation sets

14 Design of an E-R Database Schema for a Job Search Activity System my_job_id co_job_id job position_type source position job_status activity_codedescription activity_description contact_id follow-up_date follow-up job_contact event looking activity_date activity_time activity comment activity_code my_job_id job_seeker company_idco_name company stock_symbol web_site last_search_date location_id street location city zip_code state company_location referred_by first_name contact_id name contact rapor_leveltelephone title last_name prefix last_actiity_date

15 Open Design Issues Should location_id values begin with number 1 for each company? Job_type: regular, internship, contract, unsolicited Job_status: hot, warm, cold, filled, not qualified More job entity attributes: job_spec, target_date Job_contact entity: contact_id, my_job_id

16 Reduction of an E-R Schema to Tables Company = (company_id, co_name, web_site, stock_symbol) company_idco_nameweb_sitestock_symbol 1Ciscowww.cisco.comCSCO 2Symantecwww.symantec.comSYMC 3Intelwww.intel.comINTC

17 Unified Modeling Language (UML) Cardinality constraints are presented differently between ERD and UML: o ERD o UML E1E2 E1E2 R 0..* 0..1 R

18 References 1. Arlow, J., UML 2 and the Unified Process, Second Edition, Kroenke D., Database Concepts, Second Edition, Silberschatz, A., Korth H., Sudarshan, S. Database System Concepts, Fifth Edition, Silberschatz, A., Korth H., Sudarshan, S: Database System Concepts, Fourth Edition, 2002


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