Database DesignOutlineSlide 3Database Design Formalisms1. Object Definition LanguageSlide 6ODL Class DeclarationsODL ExampleODL DeclarationsODL Example ExtendedODL Declarations, ExtendedODL Example, Extended AgainODL Declarations, Extended AgainTypes in ODLCollection TypesAllowable Types in ODL2. Entity / Relationship DiagramsWhat is a Relation ?Multiplicity of E/R RelationsMulti-way RelationshipsRoles in RelationshipsSlide 23Attributes on RelationshipsConverting Multi-way Relationships to BinaryDesign PrinciplesWhat’s Wrong?Slide 28Database DesignSept. 27, 2000Outline•ODL - Object Definition Language (2.1)•E/R - Entity relationship diagrams (2.2)•Design Principles (2.3)Database Design•Why do we need it?– Agree on structure of the database before deciding on a particular implementation.•Consider issues such as:–What entities to model–How entities are related–What constraints exist in the domain–How to achieve good designsDatabase Design Formalisms1. Object Definition Language (ODL):– Closer in spirit to object-oriented models2. Entity/Relationship model (E/R):–More relational in nature.•Both can be translated (semi-automatically) to relational schemas •ODL to OO-schema: direct transformation (C++ or Smalltalk based system).1. Object Definition Language•ODL is part of ODMG•superset of Corba’s IDL •Resembles C++ (and Smalltalk).•Basic design paradigm in ODL: –Model objects and their properties.•For abstraction purposes:–Group objects into classes.•What qualifies as a good class?–Objects should have common properties.ODL Class DeclarationsInterface <name> { attributes: <type> <name>; relationships <range type> <name>; methods}Method example: float gpa(in: Student) raises (noGrades)Arbitrary function can compute the value of gpa, based on astudent object given as input.ODL ExampleProductPersonCompanycategorynamepricenamestockpricenameaddress ssnODL DeclarationsInterface Product { attribute string name; attribute float price; attribute enum Categories {electronics, communications, sports …} category }Interface Company { attribute string name; attribute float stockprice; }Interface Person { attribute integer ssn; attribute string name; attribute Struct Address {string street, string city} address; }So far just simplified C++ with slightly different syntaxODL Example ExtendedProductPersonCompanycategorynamepricenamestockpricenameaddress ssnbuysworksFormadeByODL Declarations, ExtendedInterface Product { attribute string name; attribute float price; attribute enum Categories {electronics, communications, sports …} category; relationship <Company> madeBy; }Interface Person { attribute integer ssn; attribute string name; attribute Struct Address {string street, string city} address; relationship set <Product> buys; relationship set <Company> worksFor;}relationship corresponds somewhat to pointers in C++ODL Example, Extended AgainProductPersonCompanycategorynamepricenamestockpricenameaddress ssnbuysworksFormadeByemploysmakesODL Declarations, Extended AgainInterface Company { attribute string name; attribute float stockprice; relationship set <Product> makes inverse Product::madeBy; relationship set <Person> employs inverse Person::worksFor; }Types in ODLBasic types: Atomic types (e.g., string, integer, …) Interface types (e.g., Person, Product, Company)Constructors:collection types: Set: (1, 5, 6) Bag: (1, 1, 5, 6, 6 ) List: (1, 5, 6, 1, 6 ) Array: Integer[17]structured types: Struct {string street, string city, integer zipcode}Collection Types•Sets:–order, number of occurrences don’t matter–{4,7,9} = {7,9,7,4} = {9,4,7}•Bags:–number of occurrences matter, order not:–{7,9,7,4}={7,7,9,4}, is different from {4,7,9}•Lists:–order, number of occurrences matter:–[4,7,9] different from [9,4,7]Allowable Types in ODLFor attributes: start with atomic or struct, and apply a collection type. OK: string, set of integer, bag of Address. Not OK: Product, set of set of integer.For relationships: start with interface type and apply a collection type. OK: Product, set of Product, list of Person. Not OK: struct {pname Product, cname Company} set of bag of Product integer2. Entity / Relationship DiagramsObjects entitiesClasses entity setsAttributes are like in ODL.Relationships: like in ODL except - not associated with classes (I.e., first class citizens) - not necessarily binaryProductaddressbuysaddressname ssnPersonbuysmakesemploysCompanyProductname categorystockpricenamepriceWhat is a Relation ?•A mathematical definition:–if A, B are sets, then a relation R is a subset of A x B•A={1,2,3}, B={a,b,c,d}, R = {(1,a), (1,c), (3,b)}- makes is a subset of Product x Company:123abcdA=B=makes CompanyProductMultiplicity of E/R Relations•one-one:•many-one•many-many123abcd123abcd123abcdMulti-way RelationshipsHow do we model a purchase relationship between buyers,products and stores?PurchaseProductPersonStoreCan still model as a mathematical set (how ?)Roles in RelationshipsPurchaseWhat if we need an entity set twice in one relationship?ProductPersonStoresalespersonbuyerRoles in RelationshipsPurchaseProductPersonStoresalespersonbuyerNote the multiplicity of the relationships: we cannot express all possibilitiesAttributes on RelationshipsPurchaseProductPersonStoredateConverting Multi-way Relationships to BinaryPurchasePersonStoreProductStoreOfProductOfBuyerOfMoral: Find a nice way to say things.dateDesign PrinciplesPurchaseProductPersonWhat’s wrong?PresidentPersonCountryMoral: be faithful!What’s Wrong?PurchaseProductStoredatepersonpersonAddrMoral: pick the right kind of elements.What’s Wrong?PurchaseProductPersonStoredateDatesMoral: don’t complicate life more than it already
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