Peter P. Chen Entity-Relationship Modeling Peter P. Chen Entity-Relationship Modeling Overview • Historical Background – Competing Forces – The Needs – How ERM was Developed – Fufilling the Needs • Last Twenty-Five Years • In Retrospect, Another Important Factor • The Future • Lessons Learned & Conclusions 2 Peter P. Chen Entity-Relationship Modeling Historical Background • Competing Forces •The Needs •How the ERM was Developed – Right Place, Right Time, Right Idea? • Fufilling the Needs 3 Peter P. Chen Entity-Relationship Modeling Competing Forces in Database Field in Early 70‘s (I) • In the Real World – File Systems Dominated – Commercial DBMS‘s are Based on: – Hierarchical Model (IBM‘s IMS) – Network Model (Codasyl Model) developed by Charles Bachman 4 Peter P. Chen Entity-Relationship Modeling Competing Forces in Database Field in Early 70‘s (II) • In the Academic World – Several Data Models Were Proposed – Relational Model (Codd, 1970) – Most Academic People Worked on: – RDBMS prototypes – Relational Normal Forms 5 Peter P. Chen Entity-Relationship Modeling The Needs of the DB Community in the Early 70‘s • For Software/Hardware Vendors – Integration of Various File and DB Formats – Incorporating More „Data Semantics“ • For User Organizations – A Unified Methodology for File and DB design for Various File and DBMS‘s – Incorporating More Business Rules 6 Peter P. Chen Entity-Relationship Modeling Weaknesses of Relational Model (I) Figure 2 7 Peter P. Chen Entity-Relationship Modeling Weaknesses of Relational Model (II) • No Explicit Entity and Relationship Concepts • Linking of Data is Done Dynamically via „joining“ Data Values • Certain Semantic Information Missing – Cardinality of relationship (one-to-one mapping, one-to-many-mapping, many-to-many mapping) 8 Peter P. Chen Entity-Relationship Modeling How the ERM was Developed -- Right Place at the Right Time (I)? • I Got Ph.D. From Harvard in 1973 – Thesis Title: Optimal File Allocation • Worked for Honeywell from 73 to 74 – In a 10-person Architecture Team for Next Generation Distributed System – Many Team Members Were DB Experts & 20 Years Older: – Charles Bachman, Henry Leftkovitz, John Lyon 9 Peter P. Chen Entity-Relationship Modeling Right Place at the Right Time (II)? • Joined MIT Management School Faculty in 74 – Interacted with User Organizations – They wanted a unified modeling and design methodology – Completed the ERM Paper – Most other faculty members were busy implementing DBMS prototypes 10 Peter P. Chen Entity-Relationship Modeling Concepts of Entity and Relationship Figure 2 11 Peter P. Chen Entity-Relationship Modeling An Example of ER Diagram Figure 2 12 Peter P. Chen Entity-Relationship Modeling Theoretical Foundations of ER Model •Set Theory • Modern Algebra •Logic •Lattice Theory 13 Peter P. Chen Entity-Relationship Modeling Defining ER Concepts using Set Figure 2 14 Peter P. Chen Entity-Relationship Modeling Relationship as an Ordered Tuple Figure 2 15 Peter P. Chen Entity-Relationship Modeling First ER Paper & Initial Reactions (I) •Published in ACM Transactions on DBMS, Vol. 1, No.1, pp. 9-36, March 76 • Codd wrote a Letter to the Editor – Single-spacing, several pages 16 Peter P. Chen Entity-Relationship Modeling First ER Paper & Initial Reactions (II) •The Situation then – Most People were in Religious War – I was a „New Kid on the Block“ • The Advices I got: – Dropped the ER Model – Joined one of the Religious Camps 17 Peter P. Chen Entity-Relationship Modeling The First Five Years (I) • Persistence with the ER Model – Continue to Write Papers on ERM – Organized First ER Conference in 1979 at UCLA – 2nd ER Conference Two Years Later – Now, an Annual Conference – November 2001 in Japan – 2002 in Finland 18 Peter P. Chen Entity-Relationship Modeling The First Five Years (II) • Some Academic People Started to Develop Semantics-Richer Data Models – Mike Hammer of EECS, MIT, now a guru in „reverse-engineering“ • US-AF ICAM/IDEF Project – Served as a consultant – The ERM Became the Basis of IDEF • More Companies Started to Experiment ERM 19 Peter P. Chen Entity-Relationship Modeling Related Developments in Next 20 Years • Codd‘s RM/T Model added ER Concepts • Bachman‘s Partnership Model, too. • ANSI/IRDS Standard – Adopted ERM • CASE (Computer-Aided Software Engineering) – First Major CASE Symposium in Atlanta, 1987, Keynote speaker – IBM AD Cycle – Based on ERM – IBM DB2 Repository Mgr -- ERM 20 Peter P. Chen Entity-Relationship Modeling Related Developments in Next 20 Years (II) •OO Modeling – Incorporate many concepts of ERM – Object is an implementation concept – Need more general concept of relationship • Data Mining – Discover hidden „relationships“ 21 Peter P. Chen Entity-Relationship Modeling In Retrospect: Another Important Factor – Chinese Culture Heritage • ER Modeling Concepts are Similar to – Chinese Character Composition Methods – Ancient Egyptian Hieroglyph – English Sentence Grammar Structure 22 Peter P. Chen Entity-Relationship Modeling Chinese Characters as Models of Real World Entities Figure 2 23 Peter P. Chen Entity-Relationship Modeling Commonality Principle & Composition Principle 24 Peter P. Chen Entity-Relationship Modeling Ancient Egyptian Hieroglyph Figure 2 25 Peter P. Chen Entity-Relationship Modeling Composition in Hieroglyph Figure 2 26 Peter P. Chen Entity-Relationship Modeling The Future • Some XML Components are Related to ER Concepts – RDF (Resource Description Framework) is a member of ER Model Family – quote from a W3C document – Xlink is moving from a „physical pointer“ toward the concept of „relationship“ • Theory of Web could be based on ERM 27 Peter P. Chen Entity-Relationship Modeling Extended Link is an N-ary Relationship 28 Peter P. Chen Entity-Relationship Modeling Lessons Learned & Conclusions (I) • ER Modeling was triggered by the needs – Unifying data views from top-down and bottom-up perspectives – For vendors & user organizations – Incorporating more sematics • Need to have right idea, right place, right time, and PERSISTENCE if you believe in your own vision! • Need Fresh Ideas from Other Fields, Other Cultures, etc. 29 Peter P. Chen Entity-Relationship Modeling Lessons Learned & Conclusions (II) • Entity and relationship are fundamental concepts for – Database design – Software engineering – Information system development – And others (data mining, ...) • Future: – Modeling & Design of XML – Theory of Web 30 Peter P. Chen Entity-Relationship Modeling References • ER 2001 and Previous ER Conferences – http://www.arislab.dnj.ynu.ac.jp/ER2 001/ – http://www.er2000.byu.edu/ • Chen’s papers online: – http://www.csc.lsu.edu/~chen 31.